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Saga of the Hobbit: A Decade in the Making

I remember the day well: the 28th of October 2004 is firmly embedded in my memory, when the discovery of Homo floresiensis was announced. And, I readily confess that my first reaction was disbelief.

It was a discovery that flew in the face of 150 years of understanding of human evolution.

I quickly rang my former PhD supervisor, and then mentor and close colleague, the late Alan Thorne at the Australian National University in Canberra, and he expounded similar disquiet.

We wondered and discussed whether some kind of disease or combination of diseases could have been responsible for it’s remarkable anatomy: a rather prophetic discussion with hindsight.

An incredible find

The first skeleton, was dubbed LB1 (Liang Bua cave find No. 1) and included a partial skull with most of the teeth in place, several lower limb bones, hand and wrist bones, some bones of the shoulders, ribs, and elements of the hips.

Through a combination of dating techniques on cave sediments it was estimated to be only about 17,000 years old.

LB1 was a two-footed (bipedal) ape, reconstructed to have stood just over a metre tall, and weighing close to 30 kilograms.

Even more striking, its estimated brain volume was among the smallest ever found in the hominin, or human evolutionary, group at just 380 cubic centimetres: although, this estimate has now been revised up slightly.

In many other respects its face, teeth and limb bones combined features seen in Australopithecus from several million years ago in Africa, features seen in Homo erectus from hundreds of thousands of years ago in Indonesia, some anatomical traits like living humans, and a host of bizarre features new to science.

The next year, more bones were described in another article in Nature, this time their age being extended from a fossil bearing unit dating from 95,000-74,000 years old right up to another one aged around 12,000 years old.

For many sceptics, this new evidence was important, for no longer was the Hobbit a single, aberrant, and incomplete skeleton, it had become a long lived population. Yet, there was, and still is, only one skull.

These new fossils, especially the second lower jaw and its teeth, as well as a large number of spinal (vertebrae) and limb bones were similarly enigmatic in their anatomy and resembled the LB1 remains when they could be compared.

A slow conversion

Now, I readily confess that I was slower than many to accept the Homo floresiensis hypothesis; and all descriptions of a new species are just that, scientific hypotheses that require testing.

I never published anything questioning the find, and although a couple journalists and many colleagues did ask my opinion, I declined at that stage to offer one, as advised by Thorne. It was very good advice.

The debate over the finds and their significance got very heated, and sadly, very personal. Long-held animosities began to raise their ugly head in the media, intergenerational squabbles and cultural differences about the role and weight to be given to senior scientists played out publically.

Accusations were made about carelessness in handling the bones. Fingers were pointed and individuals accused of unauthorised and unethical access to the remains.

In 2004, the first of a number of studies criticising the “new species” hypothesis was published by Thorne and Maciej Henneberg of the University of Adelaide, alongside of a response from Peter Brown of the University of New England, and others who had described them.

This article began the assault by a group of scientists suggesting the Liang Bua remains, chiefly LB1, were simply from a diseased modern human, perhaps even an indigenous person from the island of Flores, with short-statured people living there today.

My initial impression had been taken much further, but I was very uneasy. Evidence was quickly garnered by Thorne, Henneberg, Teuku Jacob, Etty Indriati, Charles Oxnard and other scientists from Australia, Indonesia, the United States and other places for pathology as the cause of the features others had come to regard as indicative of a new species.

In fact, over the last decade no less than eight diseases or syndromes have been suggested as possible explanations for the unusual features of LB1, to account for its resemblance to primitive hominins.

Yet, I began to have serious doubts. I had spent the first 10 years of my career working on early hominin fossils in Africa, and had in fact described with the late Phillip Tobias the most complete skull belonging to the earliest species of Homo from South Africa, as well as other early fossils from that country; and had worked on very ancient bones in Kenya as well.

The brain surface anatomy of LB1 was also studied on a virtual model made from CT-scans by Dean Falk and her team, comprehensive examination of the shoulder and wrist bones occurred, and then the foot bones were studied in detail.

All of the evidence was pointing to a very, very primitive brain and skeleton: one like that seen in our ancestors hundreds of thousands, if not millions, of years ago.

By 2007, I became unconvinced that a diseased Homo sapiens could end up resembling primitive hominins in so many ways. And, I told a journalist so, for the first time offering my opinion about the finds: I found the new species hypothesis convincing.

A small brain through arrested brain growth is one thing, short stature another, but the striking resemblance of so many features from across the skeleton would be too much of a coincidence and require far too much ad hoc explaining to ring true, for me anyway.

Clearly others disagreed, and continue to do so, the debate about which disease may have caused such gross disfigurement, nay evolutionary reversion, continues, the latest candidate being Down syndrome published in 2014 by Henneberg and co-workers.

The bigger picture

While it’s true that palaeoanthropology – the science of human evolution – has a history of sometimes rather extraordinary claims, and even downright frauds such as the Piltdown Man, I think the Hobbit debate has by historical standards been rather unusual.

For a start, it has lacked a larger than life colonial figure at the centre of the discovery: historically we have often seen eccentric and exuberant characters like Eugene Dubois, Raymond Dart, Louis Leakey or Robert Broom taking on the world to show how they have more or less single handedly solved a key riddle of human evolution; and in a place far from the centres of European colonial power.

While Homo floresiensis has had its enthusiastic public champions, including the late Michael Morwood, Australian co-leader of the project that discovered it, much of the ego and flamboyancy of earlier eras has been lacking, although the conviction certainly hasn’t been.

Also different this time has been the way a number of leading international scholars rallied around to support the find from its first announcement.

I guess one the key differences has been that the scientific manuscripts describing the Liang Bua finds were anonymously reviewed by senior colleagues prior to their acceptance for publication in Nature.

When Dart described Australopithecus and the Leakeys discovered Zinjanthropus this top-of-the-pops science journal didn’t require such rigorous review prior to articles hitting the printing presses, the Hobbit find was subjected to. Instead, discussion and review of the science played out through correspondences sent to Nature.

Ten years on since the announcement of Homo floresiensis we are scarcely any closer to understanding the origins and evolutionary relationships of this very enigmatic species.

While its always a precarious thing to try to second guess where the “silent majority” stands on any issue, I think its fair to say that a majority of specialists accept that the remains represent a new species of a very primitive human relative.

I also think history will show that the Hobbit stands as one of the most surprising, challenging and important discoveries made in the 150 or so year history of palaeoanthropology: up there with Dubois’ Pithecanthropus, Black’s Sinanthropus, Dart’s Australopithecus and the Leakey’s Zinjanthropus.

Apollo 11 Bootprint

Extraordinary Beginnings of Human Consciousness

Image credit: NASA

Some of the most most important questions we can ask in science are: Just who are we, as a species? What makes us so different to all other life? How did we become the kind of creature we are today?

The beginning of our species is one of the most significant events in the Earth’s – some say the universe’s – history. And it’s both a fascinating and astounding story as well.

At the centre of this question – our origin as a species, Homo sapiens – is understanding big questions like the beginnings of consciousness.

A place in the universe

The 20th Century luminary of biology, Julian Huxley, believed the evolutionary arrival of humans was so profound an event in the Earth’s history that he dubbed the geological period when it occurred the “Psychozoic Era”.

That is, the geological era of the soul or mind.

Not to be confused with the Anthropocene, of course.

Contemporary cosmologists like Paul Davies have even argued that the evolution of humans gave the universe self-awareness: consciousness no less.

We humans have always thought of ourselves as rather unique in the natural world – even special – a vast intellectual gulf seemingly separating us from all other life.

To reinforce this, we have constructed cosmologies placing humans at the centre of the cosmos: the sun orbiting the Earth – as seen for example in Ptolemy’s geocentric model of the universe – proof positive of our importance within the universe.

This view changed of course with Copernicus who showed some 1,300 years later that the sun was at the centre of universe; well the solar system more accurately, the Earth being just one of several celestial or extraterrestrial bodies orbiting the sun.

Proof of the power of the human mind, reason, imagination, and of course science: further evidence of our intellectual prowess and uniqueness as a species.

Four hundred years later came the space race. Humans, through the Apollo missions, ventured beyond our Earthly – our evolutionary – home, setting foot on our extraterrestrial neighbor.

We were struck by our seeming aloneness and insignificance in the universe: our pale blue dot of a home set against the vast black expanse of the universe.

This, and events leading up to this moment, yet again altered our thinking about our place in nature. That was especially so after the consciousness shifting revelations brought by those first steps – Neil Armstrong’s “one giant leap for Mankind”.

For me, one picture among the many from this time epitomizes more than any other this apparent gulf between us and all other life on Earth. A simple image of a footprint made on the powdery Moon’s surface.

The apparent simplicity of this image, however, masks a deeper meaning: a footprint, made by a two-footed ape, a hominin, on the surface of the moon.

With all the cultural, intellectual, scientific and technological capacity that allowed us to capture an image like this; and all the poignancy of the moment as well.

Alone in the universe?

Now, I find the efforts of these cosmic explorers to be remarkable. Its something we humans do – explore – and its at the very heart of the enterprise we call science.

And, there’s something rather poignant about our desire to see just whether we ARE actually alone in the universe.

But, there’s more to it than mere philosophy or a deep sense of curiosity. Our search for life on other planets, in other parts of the universe even, has a ring of irony to it as well.

So far we seem to be one of a kind. Yet to find clear evidence for life beyond Earth. No extra-terrestrial intelligence. We are alone in the universe.

Yet, it hasn’t always been this way, being alone I mean.

No, I’m not thinking about a lost civilization in some remote galaxy.

We are so quick to think beyond Earth to seek evidence intelligent life when in fact it was with us, on Earth, until remarkably recently.

Living with the cousins

Our ancestors shared the planet with other intelligent life not so long ago – the blink of an eye in evolutionary time – with creatures a lot like us. Yet, today they have gone, leaving us alone, and leaving us to forget their legacy.

Thankfully science is beginning to understand the role they played in our evolution and to make sure we don’t forget our past.

Aliens? Certainly not: evolutionary cousins… fellow hominins: two-footed apes. And they shared the landscape with our ancestors in Africa, Europe and Asia.

Our ancestors shared their world with them for most of our evolutionary history stretching back to around 8 million years ago, to the beginning of two-footed apes.

Being alone, as we are today, is the unusual state of affairs.

You’ve undoubtedly heard of the Neanderthals, Homo neanderthalensis? They lived up until just 40,000 years ago.

The so-called “Hobbit” – or Homo floresiensis – from the island of Flores. It lived up until around 17,000 years ago.

Or, the Red Deer Cave people, one of my own discoveries with my colleague Ji Xueping, from southwest China. Cousins that lived even more recently, up until about 10,000 years ago.

The time when humans were beginning to invent farming: domesticating plants and livestock and clearing the land to grow our food; setting things up for our modern urbanised lifestyle.

They weren’t just the ones who perished and we survived: the smarter, more successful species, destined to take over the planet. We may in fact owe them a bigger debt of gratitude than we might think.

Arrival of the mind

Our species evolved only about 200,000 years ago: probably the newest arrival on the evolutionary scene.

Yet, if we look at the evidence for the behavior our ancestors – the archaeological record – we can scarcely distinguish the behavior of sapiens-humans from our cousins.

That is, until somewhere in the geological window of time around 50, 60 or 70 thousand years ago.

Roughly three quarters of the way through our species’ evolution.

At this time, we saw a major event which archaeologists have dubbed the “Human Revolution,” and it may well signal the arrival of the human mind, Huxley’s psychozoic or even Davies’ universal self-awareness.

At this time we saw the first examples of jewelry being made.

Also at this time, humans took their first steps out of Africa – the humans who went on to the found the world’s living populations across the globe – as has been powerfully shown by genetics.

People lived for the first time in previously unoccupied areas, unavailable to our cousins; like rainforests, intensely arid zones including deserts, high mountain ranges, and they quickly settled the Arctic region.

East Asia was also settled about 50,000 years ago for the first time by humans, as was the island continent of Australia. Challenging environments with sometimes strange animals and unfamiliar plants and landscapes.

All of this occurred about the time our kind left Africa. Not earlier, and sometimes a little later. And despite the fact we had existed as an unremarkable species for around 150,000 years.

We saw the first cave paintings at this time, in Europe, Asia and Australia. Symbolic representations of the internal and external world through vivid paintings of cave and rock shelter walls.

And we saw a much wider range of tools being made, with rapid innovation in tool form and use. Tools called “Microliths”: tiny tools that replaced in many places the bigger, chunkier tools made by our earlier ancestors and relatives.

Tools perhaps bound or glued onto a spear to make say a harpoon.

In short, we saw humans in all of our glory: with our vivid internal world and imagination, and living in virtually every nook and cranny the planet has to offer.

Gift from a departing relative

So, why the Human Revolution then and not some other time during the 200,000-year span of our species? Well in short we don’t really know of course.

But we can piece together the evidence to develop a rather surprising scenario: a truly remarkable narrative of our origins, based on the latest science.

At about 60,000 years ago, when our human ancestors were beginning to make their journey to settle new parts of Africa and the rest of the Old World – Asia, Australia and eventually Europe – the world was a very different place to today.

It was a world inhabited by our close relatives: cousins living in parts of Africa, and in Asia and Europe.

Now, something rather extraordinary seems to have occurred about this time, as has been shown by the work of some very clever geneticists able to successfully extract and sequence DNA from extinct species like the Neanderthals and the “Denisovans”.

When our ancestors moved into these new places they did something that seems to be a first in human evolution – they mated with the locals.

In short, our Homo sapiens ancestors seemed to have shagged their way across the Old World, incorporating genes from different species as they spread.

One important example we know about is our coupling with the Neanderthals: a one-way affair between Neanderthal males and human females.

Now it turns out that by the time humans met up with the Neanderthals they were a species in decline – probably even a threatened species: living in small, widely dispersed groups, genetically depauperate.

And, we probably pushed them into the abyss of extinction, as we are doing today with so many other organisms.

So, may be it was a last desperate fling by the Neanderthals, a way to try to avert the inevitable.

Or, perhaps Neanderthal mates were just so rare they couldn’t afford to be fussy. Shagging that lanky, bubble-headed, Johnny-come-lately species from Africa.

Everywhere our ancestors went they made love with the locals. Different parts of Africa, the Middle East, East Asia and Europe: it was a catch cry of “Keep Calm and make love, not war!”

Yet, I expect it was bit of both – love and war – for they went extinct, unless you think we shagged them out of existence?

But here’s my real point: it seems to me that humans weren’t really capable of anything like what we think of as uniquely human until about this time.

In other words, it seems that human consciousness arrived rapidly on the scene about then.

That the universal self-awareness of Davies, or era of the mind or soul of Huxley, only began then; not before; not with the beginning of our species; but three-quarters of the way through our evolutionary history.

Patchwork genome

Now our genome, it turns out, is like a patchwork quilt. It’s estimated that up to 5% of the DNA of people living in North Africa and outside of Africa today comprises Neanderthal genes.

And a similar value also for the Denisovans – a mysterious species from Siberia we know from a single tooth and finger bone, but also from their genome thanks to the remarkable efforts of geneticists.

It might strike you as odd that different species interbreed. But, in fact, between species mating is common in nature and is actually an important source of evolutionary innovation right across life.

In our own evolutionary group, the primates – the mammalian order containing humans and other apes, monkeys, lemurs and lorises – at least 10% of living species interbreed naturally in the wild.

And, between species breeding is now known to lead to novel combinations of genes, sometimes resulting in new features or adaptations, and sometimes even new species. So it seems to be with us humans.

The Denisovans, for example, probably gave us a raft of genes associated with immune function and genes that allowed people living today in Himalayas to survive at high altitude.

We may even owe our success as a species in Asia and Australia in part to the genes they gave us through interbreeding with our ancestors.

Accidental origin of us

There’s another really fascinating and potentially profound genetic gift they gave us on their way out: a variant of the microcephalin gene.

This gene plays a key role in brain size in humans and there is ample evidence it has been under strong selection in recent evolution.

Now, genetic studies suggest this gene may actually have been added to our genome through interspecies interbreeding with a close cousin. Maybe even with the Neanderthals.

I don’t wish to suggest this is THE gene for consciousness, for without doubt something as complex as the human mind or consciousness must involve multiple genes or even networks of genes.

But, the microcephalin gene is likely to be key gene, without which consciousness might not exist.

So, it could be that the psychozoic of Huxley, or the universal consciousness of Davies, resulted from the incorporation of a gene we received from a close evolutionary relative into our own species’ genome.

A parting gift from a species on the road to extinction!

The very feature we hold so dearly as distinguishing us from all other life – our consciousness – may have evolved because of a gene we inherited from another species.

Isn’t this the ultimate irony? We get the gene, send them to extinction, and claim universal consciousness while we’re at it!

Science constantly updates and knowledge progresses. And, without doubt, this story will change as well. But, in the end, this doesn’t really matter because it highlights one really important aspect of our evolution.

It is clear that we humans, and our remarkable consciousness, were not planned, nor inevitable, and not built into some design for the universe or the fabric of the cosmos.

Instead we were accidental, our evolution contingent.

The very feature we hold so dearly may in fact result from a chance encounter in a dark alley, even an evolutionary one-night stand.

This article is based on a TEDX Brisbane talk given by Darren Curnoe on 5 October 2014 (available soon).

Human races: biological reality or cultural delusion?

The issue of race has been in the news a lot lately with the canning of proposed amendments to Australia’s racial discrimination act, attempts by extremists to commit genocide on cultural minorities in Iraq and a new book by US author Nicholas Wade that has scientists claiming their work was hijacked to promote an ideological agenda.

The idea that races are part of our existence and daily experience, especially those of us living in multicultural societies, seems to be just taken for granted by many people.

But are races real or simply social/political constructs? Is there any scientific evidence they exist in humans? Or are some scientists just being politically correct in denying their existence?

Race in nature

The “race” category has been used by biologists for hundreds of years to classify varieties of plants and animals, and, of course, humans. It has normally been reserved for geographic populations that belonging to a single species, and has often been used as a synonym of “subspecies”.

While the species concept, or definition, has also had its share of controversies, biologists agree that species are real, not arbitrary, and represent reproductively cohesive evolutionary units.

Yet the use of “race” in biology is far from straightforward. It’s been controversial for many decades irrespective of which species it has been applied too; human or otherwise.

Ernst Mayr, one of the intellectual giants of biology during the 20th century and a pioneer of the classification of biological diversity, was critical of the use of races and subspecies by taxonomists.

Unlike species, races and subspecies are very fuzzy categories. They lack a clear definition as a biological rank, being arbitrarily and subjectively defined and applied.

Races have been identified on ecological, geographical, climatic, physiological and even seasonal criteria. There are subraces, local races, race populations, and microgeographic and macrogeographic races; even “ethnic taxa”.

Races simply aren’t real like species are: species represent genuine “breaks” in nature while races are part of a continuum that can only ever have very arbitrary boundaries.

Their lack of favour in biology today has a great deal to do with a desire to remove subjectivity and fuzzy thinking from the enterprise of classifying nature.

A race to the bottom

The history of scientific racialism has a very chequered history. Many large-scale atrocities and instances of genocide were carried out in the name of race, especially the superiority of one race over another, particularly during the 17th through to 20th centuries.

Anthropology was obsessed with race from the 18th to 20th centuries and has a lot to answer for in terms of the part it played in justifying political and ideological racism.

If you doubt for a moment the impact that race has had on many people, just ask an indigenous person anywhere in the world what they think of race.

History doesn’t lie

Putting aside the ethics for a moment, is it legitimate from the biological perspective to apply race to humans? We might consider this from two viewpoints:

1. How would we go about recognising them?

2. How many races might we then identify?

Both questions were the source of regular consternation during the 20th century, and earlier, as anthropology struggled to make sense of – and pigeonhole – the geographic variation seen in humankind around the world.

What evidence was used to identify human races? Well, as it happens, just about anything, and most of it unscientific.

The book Races of Africa, published in three editions from 1930 to 1957, recognised six races inhabiting the African continent. Its author, British anthropologist C G Seligman, readily admitted that the races it described were defined on non-biological grounds, a fact which the “readers should appreciate in order to make necessary allowances and corrections”.

How were these races identified? Mostly using the languages people spoke: as Seligman further informed his readers, “linguistic criteria will play a considerable part in the somewhat mixed classification adopted.”

Seligman should be praised for his honesty. Many other anthropologists continued the rouse of biological objectivity well into the 1970s; some stick to it today. The reality is that most races were identified on cultural or linguistic grounds, or simply on account of educated intuition, not biology.

Another fascinating example of the arbitrariness of this category is the so-called “Negrito” “pygmy” race, which sometimes still gets talked about by anthropologists and archaeologists with respect to the origins of indigenous people in East Asia and Australasia.

It has been defined to include indigenous people from the Congo of Africa, the Andaman Islands, several Southeast Asian countries, New Guinea and Australia. The Negrito race is not a biological reality reflecting history, but an artificial construct based on superficial similarities.

The skull measurements, brain size estimates, hair form, skin and eye colour, intelligence and blood group data used to justify races were simply retrofitted to each of them.

Moreover, these physical features were very far from flawless in reinforcing established notions of race. None of them has provided any evidence for discrete boundaries between human groups – or groups as genuine geographic entities – and many of them simply reflect the environment, not biological history.

Take skin colour, or pigmentation, as an example, a feature that has been used in almost every racial classification published. While anthropologists employed discrete categories such as “black,” “brown” and “white,” in actuality, pigmentation grades continuously along a geographic cline from the equator to northern and southern latitudes, regardless of race.

How many races have been recognised for living people? Well, there seems to have been no real limit in practice, reinforcing their arbitrary nature.

During the 20th century, estimates of the number of races varied from two to 200 across the globe. For Europe alone, one book published in 1950 estimated six, while another one the same year identified at least 30 races.

[The books in question are: Boyd, W.C. 1950. Genetics and the Races of Man. Boston: Little, Brown & Co.; and Coon, C.S., Garn, S.M. & Birdsell, J.B. 1950. Races. Springfield, Ill.: Thomas.]

Sure, you might recognise races if you compare the skin pigmentation of people from a village in the Scottish Highlands to one in coastal Kenya. But you’d be kidding yourself because you would be ignoring all of the people who live along the thousands of kilometres that stretch between them who don’t fit into your concocted moulds.

Genetics: the final arbitrator

Developments in the field of genetics from the 1960s onwards led to new inroads into the question of race. In fact, genetics marked the death knell in the scientific race debate.

Geneticists have found a number of features about human diversity that just don’t fit the pattern expected for the ancient subdivisions we might anticipate if races actually existed.

Some important findings that show racial categories to be unfounded include:

– humans are genetically much less diverse than most mammals, including our chimpanzee cousins

– common estimates are that around 2%-8% of genetic variation occurs between large groups living on different continents; a pattern that again contrasts with most mammals, which show much greater differences on continental scales

– living Africans possess substantially more genetic variation than other populations. This reflects the ancestry of our species in Africa – only a couple of hundred thousand years ago – and the establishment of all non-African populations by a small founder group from Africa – less than 60,000 years ago

– most populations show high levels of mixed ancestry indicating that people have migrated regularly in the past, with most groups far from being isolated from each other for any great length of time.

Are we all the same then?

There is no denying that humans are variable. Some of that variation – a small amount – reflects our geographic origins. Genetic data show this unequivocally.

But this is simply not the same as claiming that this geographic variation has been partitioned by nature into discrete units we call races. Humans have simply refused to be classified along taxonomic grounds – beyond the fact that we all belong to the single species Homo sapiens.

The facts are that the races recognised by anthropologist during the 19th and 20th centuries simply don’t hold up to scrutiny from physical or genetic evidence; besides, races never were scientific to begin with.

Has human evolution come to an end?

Futurologists love to think they have the answers to questions about where we might be headed as humans: technologically, socially and biologically.

A recent example bandied about on the Internet comes from Nickolay Lamm, a digital artist who makes ‘normal-sized’ Barbie-like dolls, and who has also speculated on how the human head may look in a 100,000 years time.

He sees a world where human biological evolution will soon end and be replaced by evolution through genetic engineering.

That a hundred millennia into the future humans will be alien like with balloon-heads – from larger brains – Manga-style oversized eyes and large, flared, nostrils.

Why this particular look? It has nothing to do with fashion or sex.

Lamm believes humans will have colonised distant parts of the solar system by this time and will have engineered various physical features to cope with low light, high solar radiation and low oxygen in our new extraterrestrial home, as well as a need for greater intelligence.

Now, I’m as much a fan of science fiction as the next guy. So, let’s be frank here, these kinds of portrayals of the “future” of human evolution are just that, science fiction.

And, in fairness, Lamm apparently didn’t claim his ideas to be anything more than speculation.

As fun as thought experiments like these might be, it can be interesting to reflect on whether science has anything useful to say about what the future course of human evolution might look like.

A never ending story

Our evolution didn’t stop with the end of the Stone Age and I doubt very much that humans will ever be able to or want to take complete control over it.

We are still evolving today and will continue to do so into the future because it’s built into the basic fabric of our biology.

Evolution will always continue because of the way our DNA is encoded and replicates, and because of the fact that we reproduce sexually.

I don’t expect that the random generation of gene mutations, DNA reshuffling that occurs with recombination during sperm and egg cell production or random genetic shifts that occur from generation to generation with sexual reproduction will cease any time soon.

This is evolution on a very small scale, but it’s happening each generation and is unpredictable. And this is evolution we simply can’t and wouldn’t like to stop.

Under pressure

At the risk of being branded a futurist myself, I think we can also sketch out some larger possibilities about the sorts of evolutionary pressures that humans are now, and into the future will increasingly be, under.

What are some of the forces and changes we see that may act to drive our future evolution?

1. Top among them has got to be industrially induced climate change with its higher temperatures and greater extremes in weather, food and water shortages and greater spread of infectious diseases, among other likely profound changes.

2. The overuse of antibiotics combined with many larger numbers of agricultural livestock and the high speed of global travel and disease transmission.

3. Resistance to pesticides by insects affecting agricultural crops and disease carrying vectors like mosquitoes.

4. Rising pollution levels and the greater exposure we are experiencing to chemicals in our environment and in our food.

5. A lifestyle based around limited physical activity and focused more on technologically-aided activities.

6. Delayed conception, especially by fathers, leading to increased disease causing mutations in newborns.

Any one of these – and the list is far from exhaustive – could lead to the sort of pressures that could accelerate evolution – beyond the background rate – in human populations.

All that’s required is that some people, especially children, because of their genes, are incapable of surviving and/or reproducing in the face of these potential evolutionary drivers.

New mutations may arise, or existing but rare ones increase in number, in a population owing to such pressures. Some of them will be beneficial, others detrimental.

As a consequence, those people who can cope, or even thrive under such conditions, would leave more of their genes to future generations: plain and simple Darwinian evolution.

Changes might include in genes associated with our immune system, with heat shock protein genes, mutations in germ line cells especially spermatozoa, eccrine (sweat) gland function or even some others affecting our skeletons, muscles or nervous system.

Sound far fetched? Well actually we have a pretty good case study from recent human evolution that suggests just these sorts of changes could happen in the not too distant future or could even be happening now.

The great agricultural assault

Large-scale studies of the human genome have shown that the most rapid and important evolutionary shifts that have occurred since our species appeared about 200,000 years ago following the invention of agriculture around 10,000 years ago.

The changes were much greater than when the earliest members of Homo sapiens left Africa less than 100,000 years ago and settled new and challenging environments in Asia, Europe and Australia founding the modern populations of these regions.

The signatures of these events are very clear: more than 70% of protein coding gene variants and almost 90% of variants found to be disease causing in living people – whose ancestors were agriculturalists – arose in the last 5,000-10,000 years.

At this time we saw a remarkable shift in lifestyle, with the end of hunting and gathering and the adoption of agriculture in many places.

This was the so-called Neolithic or Agricultural Revolution, and it eventually lead onto the industrial and post-industrial economies we have today in the rich world.

Farming led to a dramatic shift in our diet, changed behavioural patterns, with less mobility but long daily activities cultivating and processing food, led to a major assault on our immune system and saw the global population rise exponentially from perhaps a few million people worldwide at 10,000 years ago to more than 1 billion by AD 1800 and 7 billion today.

It led to large tracts of land being cleared, extensive natural species and habitat loss, changed local weather patterns, permanent human settlements, high density living, exposure to many new infectious diseases from handling animals and from exposure to their faeces, contamination of water supplies and much poorer hygiene including exposure to diseases carried by pest species like rodents.

The sorts of changes we see going on in the world today as a result of human activity are in many ways similar to those during the agriculture revolution only this time on steroids!

Who will be affected?

Given the breadth of these potential drivers of current and future human evolution, all human populations will likely be affected, but not equally.

While scientific and medical progress over the last century or so has been remarkable, much of it aimed at reversing the effects of the adoption of farming, the spoils of our efforts have not been shared equally and many people in the developing world today still suffer diseases largely eradicated from wealthier societies.

These are also the people who are most vulnerable to the effects of carbon and other pollution and their various and wide reaching effects, and also the people who will be most at risk of evolutionary pressures from them.

Unlike any other time in our history, we head into this future knowing full well where we are going and without the veil of ignorance that surrounded our Stone Age or Neolithic ancestors.

These are not the glamorous changes the futurists like to focus on but they are, I think, far more plausible ones, and ones with very real implications for science, medicine, multinational policy makers and governments around the world.

The evolutionary path to us: straight line or forks in the road?

Search “human evolution” in Google images and what you’ll get is an abundance of stereotypical images of an idea deeply embedded in our subconscious, the inevitable line or ladder of human evolution:

Step 1, crouching hairy ape resembling a chimpanzee with a bad back;

Step 2, ancient ape learns to squat;

Step 3, ape corrects bad posture;

Step 4, upright ape begins to loose skin colour;

Step 5, almost-human creature has picked up a spear, grown a beard and donned a roughly hewn leather skirt; and

Step 6, big-brained pale skinned man wearing a tailored leather mini (or Armani suit if you prefer) arrives in crowing glory, carrying a beautifully crafted spear (or brief case or even mobile phone).

Now, not only is this a woefully outdated, laconic and highly inaccurate portrayal of our evolutionary history, it’s one the plays right into the hands of wannabe scientists like creationists, showing our evolution to be a programmed series of steps leading inevitably to humankind.

This ridiculously simple image would also have appealed to the racialist anthropologists who dominated my field during the 19th and, sadly, a good part of the 20th Century — scientists like Samuel Morton, Carlton Coon and many other race supremacists.

We might well also ask the obvious question: what happened to the other 50 per cent of humanity, womankind? There’s more than a hint of Genesis (2:23) about it: “this is now bone of my bones, and flesh of my flesh, she shall be called Woman because she is taken out of Man.”

But, what I don’t really get is why this kind of drivel still pervades the internet well into the 21st Century and even on some pretty reputable sites that claim some kind of authority on evolution.

So, what’s the truth about how we evolved? How should we be portraying the broad sweep of our evolutionary history?

The ultimate twig

A giant of 20th Century biology, George Gaylard Simpson, observed in a 1964 article in the journal Science in which he poured cold water over the fledgling field of “exobiology” (what we today call “astrobiology”) that:

The fossil record shows very clearly that there is no central line leading steadily, in a goal-directed way, from a protozoan to man. Instead there has been continual and extremely intricate branching, and whatever course we follow through the branches there are repeated changes both in the rate and in the direction of evolution. Man is the end of one ultimate twig.

Sadly, 50 years after Simpson wrote these words, the public portrayal of human evolution hasn’t changed much, if the internet, many people’s font of all wisdom, is truly representative.

The portrayal of evolution as a ladder, just like the equally misleading term “missing link”, harks back to the Great Chain of Being of 17th and 18th Century philosophers who believed it was their divine duty to order and name nature in accordance with God’s plan: simple things at the bottom and humans, especially the white man, at the top, closest to God.

Carl Linnaeus, the 18th Century father of biological classification, whom we have to thank for the system of scientific names we use today to label all living things, was one such creationist.

He classified humans in the Order Primates and today this label still holds, humankind sitting in a biological group with the lemurs, lorises, tarsiers, monkeys and other apes.

Being dubbed a Primate is one of the highest honours a church can bestow on a clergyman, particularly a bishop, and Linnaeus’ classification reflected his bias that humans were also, like clerical primates, close to God.

But, while the label “primate” remains today, religious baggage no longer clouds our ideas about scientific classification.

Reading the fossil record

Beginning in the first half the 19th Century, anthropologists began to amass thousands of fossils, now spanning a period of seven million years, and this record of our evolution recovered from the Earth’s crust shows unequivocally that diversity was the rule.

Latest count is more than 30 species or twigs of two-footed ape (or ‘hominin’) relatives in our evolutionary bush: or many forks in the road to us, most of them dead ends.

It’s true that most of the fossils we have are broken skulls or teeth, sitting in or out of their respective jaws, but just occasionally nature throws up a more complete skull or even nearly complete skeleton for us to find: take Australopithecus sediba as a recent example.

Yet, what’s even more fascinating to me, as odd as it may seem, is what we don’t know by way of extinct species!

The fossil record is continually throwing up surprises for us when we look in places we’ve not looked before, or sediments spanning previously neglected periods of time.

Take the Hobbit from Flores (strictly Homo floresiensis), or my own discovery with Chinese colleague Ji Xueping, the ‘Red Deer Cave people': anthropologists would never have predicted either of them to have existed based on what we previously knew.

That’s the joy of evolutionary science — not to be confused with another biological pastime — just when we think we know it all, along comes another big surprise to forces us out of old habits!

We know very little about human evolution for most of the planet, especially for vast areas like Asia, and even for most of the massive African continent.

Similarly, there are big gaps in time: until the year 2000, the human fossil record ran out at about four million years ago, but then within a few years of each other, new discoveries in Kenya, Ethiopia and Chad pushed it back another three million years, filling a vast chasm.

While the image of the “bush of human evolution” promoted by a bell-bottom wearing Stephen Jay Gould back in the 1970s might not be very glamorous it is the perfect analogy on many levels.

Not only does it accurately portray the evolutionary history of a very diverse, and rather short lived group of two-footed apes, it shrinks our collective ego back to a more realistic and moderated place, right where is should be.

Brain versus brawn: evolution of the bubble-headed weakling

One of the most important questions we can ask, and one that continues to take up much of the time of scientists, philosophers and the religious minded alike is, why are humans so different to the rest of the living world?

Philosophers and physicists have even celebrated the appearance of humans 200,000 years ago on the African savannah as marking the arrival of consciousness or self-awareness for the universe.

Despite the remarkable promise and advances of science and technology over the past 155 years since Charles Darwin published his paradigm shifting book, On the Origin of Species, I find myself increasingly pessimistic about whether this ‘riddle to end all riddles’ will ever be solved.

Mind the gap

In our quest to disentangle it, our scientific gaze usually turns to examining the differences between our close living relative, the chimpanzee, and ourselves.

The physical and behavioural distinctions between us are obvious to all: pointedly, it is we who are destroying their habitat and threatening their very existence.

We share a common evolutionary ancestor with them some 7 or 8 million years ago – a mere ripple in the stream of time of Earth’s history – and more than reason enough to ensure their survival as a species.

Our genetic blueprint, our genome, is different by a mere 1-2 percent: barely enough to explain the “gap” between us.

Surprisingly, comparisons of our genomes have shown that chimpanzees have undergone more positive genetic change in their evolution than we have, undermining the widely held view that humans are dramatically different to other apes.

This also means that, despite its promise, our DNA seems unlikely to provide the answer to this most important of questions.

Bubble-headed apes

One of the most obvious physical differences is our massive brain: a typical chimp brain is close to 400 grams in weight while a human one, on average, weighs almost one and a half kilograms.

Geneticists have identified 15 genes differing between us that physiologically control our brain and nervous system.

Some of them probably underpin the profound changes in brain growth, size and function that set humans apart, but this remains  unclear.

Fifteen genes is a very small number, bearing in mind the 21,000 genes present in our genome – most of which have no known function – and that seemingly ordinary differences between people such as stature are influenced by hundreds of genes.

Brawn over brain

Another major difference between us is resides in our brawn: it is a well known fact among zoo keepers and conservationists of chimpanzees that these animals have been known from time to time to rip the arm out of a human’s shoulder socket when angry.

While the number, structure and function of their muscles is overall very similar to ours, there are a few important exceptions such as muscles involved in walking upright, chewing our food and the expression of emotions with facial gestures.

Our limb muscles are mostly a lot smaller and weaker than a chimp’s and their joints are adapted for much greater agility and more rapid and complex movements than ours.

In short, human limbs have evolved for terrestrial running, while the chimpanzee’s are adapted for arboreal climbing.

The differences in our chewing muscles obviously reflect our diets, with humans preparing our food using techniques like cooking, a practice that may have begun a couple of million years ago among our Stone Age ancestors.

Another really interesting and long understood difference is in our muscles of facial expression, crucially used for non-verbal communication in both species.

Charles Darwin in his 1872 book The Expression of Emotions in Man and Animals wrote about how important facial gestures were in distinguishing humans from other animals.

Yet, recent research comparing these muscles has shown that earlier scientists exaggerated the differences between humans and chimpanzees, and that our facial muscles are very similar in number and function, although, not identical.

Chimpanzees do possess a very wide repertoire of facial expressions and gestures, but they are not as varied as ours: it seems that only humans express emotions like disgust with our faces.

Facing the question with new energy

The seeming failure of genetics to explain “the gap” seems to be inspiring some rather novel ways to address the problem.

Fascinating new researched by Katarzyna Bozek and co-workers published in PLOS Biology has compared the so-called “metabolome” of humans and chimpanzees with some surprising results.

The metabolome is the totality of small molecules produced in the body during metabolism (i.e. normal processes that occur within the cells).

They include amino acids, sugars, fats, vitamins, pigments, odorants, hormones and other signaling chemicals, enzymes and many others.

There are almost 42,000 such chemicals known for the human body, and Bozek and colleagues compared 10,000 of them from five body tissues from the brain, kidney and muscle.

Importantly, they found that changes in these chemicals between species track evolution and reflect the amount of time and change between organisms since they shared a common ancestor.

Reassuringly, they found that the human metabolome for the brain, especially our frontal cortex, had changed four times more rapidly than in chimpanzees, reflecting major differences in brain size and function between us.

But the big surprise in their research was that human muscle metabolome had changed more than eight times as much in humans than in chimpanzees, hinting at major differences in the way our muscles work on the molecular level.

They very reasonably speculate that metabolism in the human brain and muscles could have evolved in tandem in such a way that the energy demands of our muscles reduced to allow our metabolically expensive brains to grow larger in evolution.

Alternatively, the shift in our ancestors to endurance running at much the same time that their brains began to enlarge may have forced a change in the major source(s) of energy used by the body as cellular fuel: perhaps relying much more on energy stored in body fat.

Undoubtedly, we still face a major chasm in knowledge about how we evolved to be so different to other apes, in the way we think and behave.

But, new approaches like those comparing our metabolomes, made possible with recent development in fields like biochemistry, offer power new insights that will add much to more traditional approaches such as anatomy, paleontology and genetics.

Why are we so fascinated by the Neanderthals?

The Neanderthals (scientific name: Homo neanderthalensis) are a species of extinct human relative (technically ‘hominin’) that occupied Europe, West and Central Asia, living from around 400,000 to a little less than 40,000 years ago.

Science has known about them for more than 180 years now and they were the first extinct hominin to be discoveredpushing our understanding of human origins beyond a Biblical timeline for the Earth.

Scientists studying human evolution are fascinated by them for a multitude of reasons; with more written about them than any other extinct species. For example, 2014 has already seen dozens of scientific articles published about them and we’re not even halfway through the year!

The Neanderthals are also deeply embedded in Western culture as the archetypal “caveman” and have historically been given a bad wrap. In the English language, we even use the term “Neanderthal” in a derogatory way to describe an ignorant or unenlightened person.

So, why the fascination with them?

A little bit of history

The first Neanderthal fossil was found at Engis Cave in Belgium by Philippe-Charles Schmerling in 1829. Schmerling found fragments from the skull of a Neanderthal child. Slightly earlier, in 1823, a fossil had been found at Paviland Caves in Wales, but we now know it to be a member of Homo sapiens.

Quite remarkably, these two European caves provided the earliest evidence for humans living beyond the timeline inferred from the Bible. Paviland is now thought to be around 30,000 years old, while Engis is still of uncertain age, but older than Paviland Cave.

The first skull of an adult Neandertal was found at Forbes‘ Quarry in Gibraltar in 1848. But, it wasn’t announced to the scientific community until 1865. The most important of prehistoric human remains from this time were, however, those recovered from the Neander Valley in Germany in 1856 at a site called Feldhofer.

The Feldhofer Cave skeleton came to light during quarrying, much of it destroyed before being rescued by a local teacher. The top part of the braincase survived and was examined by the anthropologist Hermann Schaafhausen. He drew attention to its “savage” and “brutal appearance” implying great antiquity.

When his work was eventually translated into English, the amateur archaeologist George Busk emphasised several ape-like characteristics, such as its pronounced eyebrow ridges.

The famous anatomist, founder of human evolutionary science and “Darwin’s bulldog”, Thomas Henry Huxley, published the first detailed study of the Feldhofer fossil in 1863. While acknowledging it to be the most ape-like of fossils found so far, he felt that on account of its large brain, it would have fallen within the wide range of variation for living humans

At the time, the human brain was considered the cardinal feature that distinguishes us from all other organisms, including our Stone Age ancestors.

At least one worker felt the Feldhofer Neandertal was distinct enough from humankind to belong to a different species, and in 1863, William King dubbed it Homo neanderthalensis.

Soon after, more Neandertal remains were recovered, yet their place in human evolutionary history was far from settled, with scepticism from several scientific quarters. Only with the discovery of several further Neandertal remains at Spy in Belgium in 1886 were the sceptics were beginning to be silenced.

Another important figure from the early 20th Century time was the French anthropologist Marcellin Boule. He believed that the Neanderthals had played no role in the evolution of contemporary humans, but were instead a very primitive evolutionary side-branch or dead end.

Boule did all he could to portray the Neanderthals as brutish, stupid and very different to humans. It is fundamentally because of his work that we see them in popular culture as an unsophisticated cave dweller, the archetypal dumb “caveman”.

For the remaining 20th Century up until today, the precise place of the Neanderthals in evolutionary history has been hotly debated. Importantly, anthropologists have argued about whether they played a role in our evolution – as direct ancestors – or were simply close (?kissing) cousins.

When and why did they disappear?

Current evidence suggests that the Neanderthals disappeared around 40,000 years ago, perhaps slightly more recently. This is about the same time that H. sapiens settled Europe after our ancestors migrated out of Africa maybe 60,000 years ago.

We don’t yet know why they disappeared, just that it is broadly coincident with modern humans settling Europe. Yet, they seem to have overlapped for several thousand years or more in West Asia (Middle East) and probably even interbreed with H. sapiens in this region.

The sequencing of DNA from several Neanderthals and comparisons with the DNA of living people from Asia and Europe has provided a pretty convincing case that we interbred.

I’ve written several articles about this topic for The Conversation and in my blog if you wish to read more about the topic (see links below), but recent evidence suggests that while we interbred, it was likely to have been mating between different species. This is surprisingly common in nature.

Even if we interbred with them, which seems reasonable, they were not our ancestors as such.

The ancestors of Europeans seemed to have hung around Asia for 10,000 years or more before they migrated into Europe. Why? Was it because of the climate? Or, because of competition with Neanderthals? Were the Neanderthals already in decline before modern humans settled Europe, providing impetus for the colonisation of the region by our species?

Latest ideas about our cousins

Over the last month since my last blog, some interesting papers about the Neanderthals have been published. I’ll outline the findings of two of them that received quite a bit of media attention to give you a taste of some the current research on them and how our ideas about them are changing.

More on DNA diversity

In the first one, authored by Sergi Castellano and a large team of geneticists and published in PNAS, the DNA of two Neanderthals – one from Spain dated ~49,000 years old and one from Croatia aged about 44,000 thousand years – was studied to try to understand how much diversity there was in the species.

The team studied more than 17,000 genes that produce proteins, or play a role in the physiology of the body, comparing them to the DNA of living people.

We know that in our species, genetic diversity is quite low, especially compared to our living cousins, the chimpanzees, even though there are 7 billion of us. This is because we all descend from a very small Stone Age population living in Africa around 200,000 years ago.

Also, genetic diversity can be an indicator of recent evolutionary history and, when it is especially low, a species is vulnerable to extinction. This could have been an issue for the Neanderthals.

It seems that the Neanderthals had much less genetic variation (diversity) than living humans and probably lived in very small and isolated groups.

Other important findings of this research relate to the particular genes that have changed between Neanderthals and us after we shared a common ancestor 500,000 years ago or more.

Castellano and co-workers found that after the split, Neanderthal DNA shows an abundance of gene changes related to metabolism, the cardiovascular system, hair distribution, and physical features affecting the genitals, palate, face, limb extremities, joints, fingers and toes, thorax, and other parts of the skull. There is also evidence for even later changes to genes involved in the curvature of the spine.

In modern humans, they found a large number of changes in genes associated with skin and hair pigmentation (colour) and also some behavioral traits. In the latter group, they identified genes that are clinically associated with disorders like psychomotor retardation, autism and Tourette syndrome including some involved in “hyperactivity” and “aggressive behavior.”

It is difficult to know precisely how these genes would have affected the behavior of our Ice Age ancestors. Human behavior is controlled by much more than just our DNA, the authors concluded that even if these genes changes affected behaviour,

“…the way in which they occurred is unknown. For example, if they affected activity or aggression levels, it is unclear whether they increased or decreased such traits.”

More on the Neanderthal Demise

The second and final research article I’ll discuss was published by Paola Villa and Wil Roebroeks in PLoS One. It set out to test whether the archaeological evidence for Neanderthals indicates that they were behaviourally less sophisticated than Ice Age modern humans: yet another study in a long history of such investigations beginning with Boule.

A common view is that (quoting Villa and Roebroeks),

“the disappearance of the archaic populations, including Neandertals, is routinely explained in terms of the ‘’superiority’’ of modern humans, who had developed in Africa the ability to evolve complex cultural traditions and had become equipped with cognitive capacities which allowed them to expand globally and replace all other hominins.”

They undertook a detailed review of the archaeological evidence for Neanderthals comparing it with similar evidence for modern humans who lived about the same time. In particular, they examined issues such as:

  • Language and symbolism,
  • Hunting methods and diet,
  • Organised use of space,
  • Capacity for innovation,
  • Size of social networks, and
  • Hafting Procedures, Heat Treatment and Cognition (i.e. tool making as evidence for complex thinking).

They end their review concluding,

“…as we tried to show here, the Neandertal archaeological record was not different enough to explain their demise in terms of inferiority in archaeologically visible domains. Thus, if Neandertals were not technologically and cognitively ‘‘disadvantaged’’, how can we explain that they did not survive?”

Well, actually, they don’t in the end have an answer as such. They conclude that there was unlikely to have been a single cause and that it certainly wasn’t the result of more sophisticated behaviour by migrating modern humans.

As I noted above, the DNA evidence suggests they could have been vulnerable to extinction on account of their low genetic diversity and living in small and isolated groups.

To be frank, I’m pretty skeptical that we can really get at the cognitive (thinking) capacities of any hominin by looking just at archaeological evidence. There is so much missing (e.g. wooden tools) and we don’t really understand the reasons why certain types of tools were made or how they were used or why they took a particular form over another.

Neuropsychologists experimenting with living people have difficulty enough understanding how the brain functions and why people do the things they do, even when they have the luxury of being able to study their brains with sophisticated techniques like magnetic resonance imaging and asking people questions in surveys.

We don’t have fossilised brains and have no chance of really understanding why particular choices were made or cultural traditions developed.

Moreover, we know that many other animals are capable of very complex behaviours as well but this doesn’t mean that their brains function the same way as our does.

Different species have brains that function differently, and clearly also have distinct behavioural repertoires. How can it be any other way?

I find stone tools to offer a crude window into past behaviour and motivations and think that we need to be a bit more careful in claiming thinking capacities from whas is ultimately very limited evidence.

Why the fascination?

In the end, our fascination with the Neanderthals stems from a long historical knowledge of them (over 180 years) and the place of them in history in overturning old/creationist ideas ; the fact that we shared the landscape and seem to have interbred with them; the deeply felt link we feel with them – they are almost, but not quite us;  the insights they provide into a lost world, and how we evolved; and perhaps revealing an even deeper (more natural or “animal”) side to ourselves and our psyche.

Further reading

Not the Marrying Kind

Neanderthals and Humans: an Interspecies Affair to Remember

Women Sought for Neandertal Surrogacy? Not Yeti, Thankfully

Sex with the Cousins: Things Are Beginning to Firm Up

Sex with Our Evolutionary Ancestors? Proceed with Caution 

Sex with Our Evolutionary Cousins: What’s Not to Love?

The deepest account: science and human origins. Part 1.

This is the first of many blogs I will devote to considering some of the scientific evidence for where humans belong in the tree of life and what makes us unique.

They will set out to answer some fundamental questions that drive me in my science but also which are so basic that they touch each and every one of us in the profoundest of ways.

Questions like:

  • Just what kind of an animal are we?
  • What’s our place in nature?
  • Who are our closest living relatives?
  • Why are we so different; or are we?
  • Was our evolution accidental (contingent) or driven by some deeper trend, process or influence?

These dominate my thinking and are central to my scientific research. The answers are deeply profound, excite me enormously, and I plan to share them with you in the blogs I write.

Hidden messages in origins stories

Each and every culture has had its stories about where humans came from, and they nearly always involved the first people being made by the hands of a divine creator.

Sometimes we were thought to have been formed from a substance such as clay or mud; or to have budded from a tree of life residing in the underworld; or even falling from the sky or being placed on Earth by a supernatural entity, already formed.

Whether we accept such stories as literally true or otherwise is not really the point.

They were stories told by our ancestors, and are sometimes still told today, because of the deeper meaning they hold for us.

They remind us of our profound connections with each other as human beings and also to the natural world.

Modern science offers us a purely physical account of human origins; that is, one without the presence or action of a supernatural force.

Yet, it also contains a profound message about connections and shared history; and one that runs much deeper, and is more moving, than any myth ever told.

It is an account founded in real physical evidence accumulated by biologists, anatomists, archaeologists and geneticists, and verifiable by anyone with a little training; and without having to accept wisdom handed down through the generations from some higher authority, human or otherwise.   

Scientific explanations

We now have sufficient account from the material processes we see around us and experience in nature each and every day to explain how we humans began.

Scientists don’t resort to explanations involving supernatural entities or forces because they would require us to make untestable assumptions, and also because they raise many complex and unanswerable questions:

  • Where did this presumed supernatural force come from?
  • Where does it reside?
  • How does it work?
  • If it is conscious, why did it create us?
  • What are its motivations?

I’ll leave these to the theologians.

The physical evidence we have for our evolution is complicated, to be sure, but it is amendable to examination and testing through common sense and through the laws, theories and techniques scientists have established since the Renaissance.

The scientific method has shown how humans are made of the same basic stuff – chemical molecules, structures, organs and bodily arrangements – as other life: information missing from traditional accounts of creation; unless we take “mud” or other such substances as a metaphor, which we might reasonably do.

It shows how humans evolved in accordance with universal mechanisms – including natural selection and random genetic drift – that have affected all species alive today and in the past.

Moreover, it shows in the deepest way possible, right down to the basic molecules that grow, shape and sustain our bodies, how we humans share a common history with all other life on planet Earth extending back some 4.5 billion years.

There is no deeper connection than what we see in the chemicals we carry in each and every cell in our bodies, the blood pumping through our veins and the organs that allow us to move, breath, eat and think.

A very primate heritage

So, just where in the tree of life do we belong then?

We humans are a primate: the “leading” animal, or group of mammals, 18th Century naturalists and philosophers thought was closest in resemblance to God (in the church, the “primate” is the head priest).

The Order Primates, as used as a category in science today, includes all living and extinct lemurs, lorises, tarsiers, monkeys and apes.

Yet, even as far back as Ancient Greece the philosopher Aristotle (384-322 BC), and in Ancient Rome, Pliny the Elder (c23-79 AD), described strong resemblances between humans and monkeys; they were yet to learn about the apes.

It is to these Greco-Roman philosophers that we owe an even more fundamental debt as scientists, for they first proposed the proposition that nature is governed by natural laws that can be investigated and understood through an inquiring mind and human reason.

Just what are these similarities between us and the other primates? Like other primates, we have (for example):

  • Grasping hands and feet, with five digits on each hand and foot, and a grasping big toe or thumb,
  • Our skeletons have two forearm (radius and ulna) and two leg (tibia and fibula) bones,
  • We can rotate our forearm bones across each other – think of the movement when you have your palm facing upwards and then turn it to face downwards, this is common to primates,
  • Our skulls comprise very similar bones, with our eye sockets enclosed by a bony bar,
  • The muscles that move our skeleton are very similar in number, arrangement and function,
  • We have fingerprints,
  • Our brains are large,
  • Our eyes face forward, and we have a well developed sense of vision, but relatively poor sense of smell,
  • We share a defined period of adolescence with a growth spurt, and
  • We have complex social lives.

Just aping about

Without doubt, humans are an ape: a fact established way back in the 18th and 19th Centuries through the dissection of monkey, ape and human cadavers, demonstrating profound physical similarities between us all.

The French naturalist Comte de Buffon (1707-1788), for example, observed:

“At what distance from man shall we place the great apes, which resemble man so perfectly in bodily conformation?”

Comparisons of the DNA contained in the nucleus of our cells, the very molecule of inheritance, shows the human genome to be most similar to the DNA of living chimpanzees, and in turn gorillas, then orangutans, then the gibbons or lesser apes, then African, then Asian monkeys and so on.

We humans share with the apes the following features (note that some of them are shared also with monkeys; list not exhaustive):

  • Stereoscopic vision (or seeing in 3-dimensions),
  • Eye sockets that are completely enclosed by bone, except where they open for us to see out of course,
  • No tail (or lack of caudal vertebrae),
  • Shoulder and hip joints that are capable of very wide ranges of movement,
  • Our shoulder joints are placed to the sides of our bodies, rather than beneath them,
  • We have 32 adult teeth,
  • Teeth with relatively simple surfaces, essentially adapted for fruit eating,
  • Broad faces with wide noses and jaws,
  • Large brains compared to the size of our bodies,
  • An intimate association between the developing fetus and the maternal blood stream,
  • We most commonly give birth to single offspring,
  • Large body sizes: especially so in the great apes (orangutans, gorillas, chimpanzees and humans), typically from around 30 kg to 200 kg depending on the species and sex,
  • Female monthly reproductive cycle,
  • Long life spans, with each segment (gestation, infancy, adolescence, adulthood) comparatively long, and
  • Very complex social lives.

The following table illustrates the approximate time of each stage of life in various primates.

  Prenatal Infantile Juvenile Adult
Lemur 2% 3% 8% 87%
Monkey 2% 5% 21% 72%
Chimpanzee 2% 8% 16% 75%
Human 1% 3% 22% 74%

Note: this table has been updated since the blog was published on 13 April 14 owing to errors in the original source.

 

It tells a powerful story in its own right, highlighting similarities between us and other great apes, as well as helping to explain the differences among different primates.

We humans are clearly exceptionally similar, as a species, to other primates in terms of our lifespan and life pattern, but there are important differences as well: about 1-3% of our lives is spent in the womb, 3-8% as infants, 8-22% as juveniles and 72-87% as adults (Note: the human data would be from traditional, hunter-gatherers).

Thus, we are born very precocial, have a short infancy, but a long juvenile period; the time we spend learning as juveniles is at the expense of our adulthood (i.e. we loose time because of it), but it is absolutely essential, as apes, to our learning the necessary skills we need to succeed as adults in a complex world.

A matter of complexity?

With so many similarities between us and other apes we are faced with a conundrum.

How is it that humans can be so different, especially in terms of our behaviour, when we are fundamentally (biologically) so similar to other apes?

This is a vast topic, spanning many areas of science and even philosophy, and one I can’t possibly do it justice here.

Instead, I will tease it out across many blogs, getting at it from different angles and points of view, from the perspective of an anthropologist studying human evolution.

To make a start though, one old idea, going back to at least the 19th Century, is that evolution is characterised by “progress”; with organisms progressing from simple to complex through time, with humans epitomizing this process.

Even 20th Century biologists held the view that complexity resulted from the accumulation of DNA changes driven by natural selection over billions of years and culminating in human intellectual and technological sophistication.

It’s a view that holds sway even today in some quarters of biology, and permeates anthropology.

But, for those scientists unfamiliar with the amazing new information emerging from the burgeoning field of genetics, especially in the genomic era, it will come as a shock to learn that this view has been shown to be fundamentally wrong.

One way to think about complexity is to simply count the number of genes in the genome of an organism.

According to this old idea of progress, used by 20th Century biologists, more complex organisms should have vast numbers of genes, well in excess of simple organisms.

Until recently, geneticists were unable to estimate with any accuracy the numbers of genes present in the genome of most organisms; it was only with the availability of gene sequencing from the 1990s onwards and the dramatic increase in computer power and drop in cost that this has become possible.

So, let’s take a look at some examples:

Organism Number of genes (approximate)
Bacteria 2,000-22,000+
Malaria parasite and yeast 5,000
Fungi 10,000-18,000+
Fruit fly 14,000
Zebra finch 18,000
Opossum 18,000-20,000 (estimated range)
Domestic dogs 19,000
Monkeys and domestic horses 20,000
Chicken 20,000-23,000 (estimated range)
Humans, chimpanzees and gorillas 21,000
Rats and cattle 22,000
Arabidopsis (flowering plant) 25,000
Papaya 29,000
Maize and grape vine 30,000
Aphids 34,000
Tomatoes and potatoes 35,000
Soybeans 46,000
Rice 50,000

It’s pretty clear from the list above that humans are nothing special in the gene complexity stakes.

On the contrary, rats and cattle, flowering plants, food crops like papaya, maize, grapes, tomatoes, potatoes and rice, and even the aphids that feed on economically important plants, have more genes than we do!

The study of DNA, especially those genes associated with organs such as our brain, does offer much promise in the search to understand why humans are so unusual.

But this research is beginning to show that even the same genes can function quite differently in the brains (and other organs) of different species; so, even having the same genes doesn’t mean your body or behavior will be the same.

There is a real caution here also for those scientists studying the DNA of our extinct relatives like the Neanderthals, for even if they have some of the same genes as us, they might have done quite different things physiologically on account of them sitting within a different genome.

But, simple exercises like tallying the number genes obviously offer no real insights into such important questions; despite what many biologist thought for many, many, decades.

Moreover, the old idea of evolutionary progress from simple to complex cannot explain the evolution of life in general, and simply fails to account for our uniqueness.

Promising paths for research

Ultimately, the search to understand why humans are so different to other organisms – with our complex and symbolic language, sophisticated culture, and heavy reliance on technology – can only be understood through varying and complimentary perspectives.

Some of this understanding comes from looking at our shared heritage with other primates: we would be nothing without our grasping hands, large brains, stereoscopic and colour vision, small and simple teeth, capacity for language and culture, use of tools, and rich and complex social lives.

Yet, these primate features on their own do not explain why humans are so unusual; why we, and only we, create art and literature, build cities, invent religions, practice science, and explore the solar system and beyond looking for clues about our identity and existence.

How farming changed us

For a long time archaeologists, biologists and historians believed that the origins of agriculture more than 10,000 years ago marked the end of human evolution.

The beginnings of civilization – and eventually of industrialization – were seen as simply reinforcing this notion.

Humans had altered the environment to such a great extent that the forces acting on hunter-gatherers through natural selection were simply no longer important. Culture came to dominate entirely, biology being now largely irrelevant to the chronicling of the human story.

That by shaping our environment – today even on a planetary scale – we had taken hold of our own biological destiny as a species.

It turns out that this view is largely wrong. Farming and subsequent developments in human history have dramatically altered, sometimes intensified, our evolution, rather than halting it.

Human evolution didn’t finish at the end of the Stone Age, it continues even today, but in many ways the drivers of natural selection have changed and have been influenced greatly by culture.

This is in part – a major part – why the quest to find some kind of palaeolithic ideal lifestyle or diet is ultimately futile; just a fad not founded in science.

Farming marked a major shift in our evolutionary history resulting in physiological changes associated with our ability to digest certain kinds of foods, dramatically altered our immune system, and changed our relationships with plants and animals in profound ways.

It may even have changed the colour of our hair and skin, according to new research by Iñigo Olalde and co-workers in Nature and by Sandra Wilde and her team in the Proceedings of the National Academy of Sciences USA (PNAS).

End of paradise

Archaeologists believe that agriculture began around 11,000 or 12,000 years ago in two regions, and independently: West Asia (Middle East) with the domestication of wheat, and animals like goats, and in China, with the domestication of millet, rice and pigs.

Dogs may have been domesticated at the same time. While various claims have been made about dogs being bred by hunters and gatherers, perhaps tens of thousands of years ahead of farming, they remain controversial.

Agriculture was also invented at a later time in parts of Africa, the highlands of New Guinea and in the Americas, probably also independently of events in West and East Asia.

The beginnings of farming – what archaeologists call the Neolithic (“New Stone Age”) – were at a time when the world’s climate began to change at the end of the last Ice Age.

Warming occurred quite quickly following a relatively short cooling event known as the Younger Dryas (or “Big Freeze”), which lasted from around 12,800 to 11,500 years ago.

The period of warming that followed the Younger Drays marked the beginning of what geologists call the Holocene (or recent) epoch, the geological time we live in today, and it seems to have been one of the major catalysts for farming.

In fact, even where farming was introduced to other places (e.g. Southeast Asia and Europe) at later times (4,000 or 5,000 years ago), there seems to have been, at least in some instances, a clear association with changes in the climate.

Climate change on its own is not enough to explain such a major shift in human ecology and economy though. People had been hunting and gathering for close to 200,000 years, and some people still do today.

So, there was no inevitability to its development, nor was it part of an unbreakable historical and social continuum, despite what some 19th and 20th Century scholars had thought.

Archaeological evidence suggests that certain human populations had become more sedentary at this time, probably due to climate related environmental change, and so both thought about and used their environment in a different way to their ancestors.

We know, for example, that pottery was being made in China from about 20,000 years ago, probably for cooking, but maybe also for storing food during lean times. It’s use became more common during the Holocene, especially with farmers.

And people were also using the wild precursors and relatives of various plants like wheat, millet and rice, and rather than just gathering them, began experimenting with them, including cultivating and then breeding them, before farming eventually emerged.

Many hunter-gatherers today and in the recent past cultivated economically important plants without farming or domesticating them, and some farmers even returned to hunting and gathering.

Farming’s real impacts

Farming has been a profound changer of the planet. Everywhere that it was introduced, farmers cleared the land to make way for agriculture: wet or dryland forms.

There are long sediment cores from lakes in many areas like China, for example, that show powerfully the devastating effects early farmers had on the landscape.

The effects of farming were also profound for the people who adopted it, in both positive and negative ways.

It led to a population explosion – sowing the seeds (excuse the pun) – for the vast numbers of people alive on Earth today. Estimates suggest a worldwide population of just a few million people 10,000 years ago grew to today’s 7 billion, and within only a few hundred generations.

While the precise reasons why the population exploded are not yet clear, it seems that the food security enjoyed by these early farmers – many hunter-gatherers were plagued by seasonal shortage and starvation – and apparent improvements to childhood survival from improved food availability were enough to cause a population boom.

At the same time, though, early farmers were exposed to a stack of new infectious diseases acquired from the animals they were now domesticating and handling through animal husbandry.

The vast majority of diseases suffered by people today around the world are zoonoses – acquired from animal sources or vectors – and most of them became an issue for humans with the domestication of animals and the clearing of land for farming.

The flu, common cold, measles, leprosy, cholera, smallpox, TB, schistosomiasis and many other infectious diseases prevalent today or in the recent past result from contact with animals in the form of animal husbandry, exposure to animal and human excrement, and contact with pest species like rodents that occurred more frequently with farming and a much more sedentary, and ultimately, urbanised lifestyle.

It’s likely even that malaria only became a major problem for humans with land clearing and changes to waterways by early farmers, but the scientific jury is still out on this one.

So, farming shaped our immune system, following the onslaught of these many new diseases, and through natural selection it even changed our red blood cells conferring resistance to malaria in some individuals.

In the face of major shifts in diet and behavior, natural selection also resulted in many genetic mutations arising; or in some instances already present mutations increasing greatly in frequency within human groups.

Such genes included those associated with lactose tolerance in adults, the metabolism of alcohol, detoxification of plant food compounds and the metabolism of protein and carbohydrates. There must be many more that are yet to be discovered, and some that may even underpin the many intolerances and allergies suffered by people today.

At the same time, major demographic shifts saw changes in the genetic variability and the composition of population gene pools.

Recent large-scale studies have found that more than 70% of protein coding gene variants and almost 90% of variants found to be deleterious in living people – whose ancestors were agriculturalists – arose in the last 5,000-10,000 years.

The rise to such large numbers in these disease causing gene variants is the result of the population explosion associated with early agriculture and gives a very real sense of how our diseases and lifestyle have been dramatically shaped by this practice.

Farming also changed our anatomy and physiology in sometimes quite surprising ways.

Sandra Wilde and her team sequenced the DNA of human remains from early farming and Bronze Age skeletons from Eastern Europe. Their study showed that changes to pigment producing genes occurred after farming arrived in the region around 5,000 years ago.

They suggested that the combination of light hair, eye and skin colour seen in Europeans may have resulted from a diet poor in vitamin-D and the need to produce more of it through increased UV light exposure and absorption.

Yet, anthropologists had thought that depigmentation was probably around much earlier, in hunter-gatherers, owing to limited UV exposure in Northern Europe. It may even have characterised the Neanderthals.

So, this new view is a major challenge to prevailing wisdom and suggests that pale eyes, hair and skin may be a very recent adaptation, or at least, only arose to high frequency very late in our evolution.

The other study, by Olalde and co-workers, actually fits with this idea rather well and quite independently. They sequenced the genome of an approximately 8,000-year old male skeleton from Northern Spain and found that his genes showed he had pigmented skin but with blue eyes; a combination not found today in people of European ancestry.

The work shows that the spread of light skin pigmentation genes through natural selection was not complete in some European populations by the end of hunting and gathering; that the genes responsible for light eye colour may have evolved well ahead of changes in skin pigmentation.

This would suggest that these late hunter-gatherers were actually physically rather different to people in Europe today and that depigmentation occurred rather late, perhaps several times, and in association with farming.

There are many other fascinating aspects of this crucial event in recent human evolution, but I’m afraid, they’ll have to wait for a future post!

 

Not the marrying kind

The idea that our ancestors interbred with other hominins like the Neanderthals or Denisovans is a truly captivating one.

The ancient DNA evidence would seem to have just emerged out of the blue, changing our thinking on how our evolution unfolded, and in a rather profound way. Is it really that amazing? Revolutionary even?

Like so many areas of science, few ideas are truly original. So much of what we write and think about today in anthropology was actually thought up during the 19th Century, well before a proper fossil record had even begun to emerge.

I guess its fair to say that there are only so many ways we can interpret our evolution, and lots of binary opposites exist and freely enter our imagination. So, much of it was dreamt up more than a hundred years ago, especially by luminaries such as Thomas Henry Huxley.

In the case of the recent evidence for interbreeding though, it’s the methods used and results found that are so remarkable. Who would have thought just a decade ago that we would have the draft genomes of several extinct human relatives sequenced? And so fast! The speed of technological change has been breathtaking.

We now have the genetic blue print for Neanderthals and the Denisovans (who ever they are).

But, we must be careful with this new information, for organisms are clearly much more than simply the sum of their genes. Possessing a genome sequence goes only a small part of the way to understanding Neanderthal (or Denisovan) anatomy, physiology, ecology, behavior and evolution.

For example, the same gene mutation sequence might appear in the genome of Neanderthals and modern humans, but it may express different proteins in one species compared to the other, or may even be non-functional in either or both. So, its presence may not mean very much at all.

As tempting as it is to mine into the genome of these ancient hominins for simple answers to their – even our – evolution, we must be careful to resist the seductive simplicity of reductionism.

The idea of interbreeding has itself been around for some time – more than 100 years in fact – in varying guises, and is sometimes couched in terms like “degeneration,” “reticulation” or “assimilation”. Yet, these terms have often come to mean interbreeding between long isolated (divergent) subspecies in human evolution, as was the view of my late postdoctoral supervisor Phillip Tobias.

He felt that Homo erectus, modern Homo sapiens, and everything in between, were simply subspecies (i.e. temporal or geographic variants of a very long lived single species, Homo sapiens).

Interbreeding on a large scale lies at the core of the so-called “Assimilation” hypothesis set out in the 1980s by Fred Smith and others to explain the origin of modern humans. It’s an idea that budded off from the “Multiregional” scenario developed by Wolpoff, Thorne and Wu in the early 1980s, based on Weidenreich’s and Dubois’ earlier ideas. The key difference is the strongly dominant role Africa played in our evolution, recognised in the former idea, not the latter.

Assimilation is one of four scenarios proposed during the 1970s-1980s to explain the geographic location, timing and process by which our kind (Homo sapiens or sometimes modern Homo sapiens) evolved. Its proponents believe that modern humans exiting Africa perhaps 60,000 years ago and widely interbred with (assimilated or absorbed) the other (archaic) hominins they encountered along the way.

Again, it was a process within a single species.

Supporters of Assimilation – like Fred Smith and Eric Trinkaus – have seen evidence for interbreeding in the form of anatomically mixed fossils for decades, in Africa, Europe and Asia. My late and dear friend Alan Thorne also thought the same for some of the European fossils, as did the late Jan Jelinek.

Claims for hybrids such as the Skhul (Israel), La Ferrasie (France), Abrigo do Lagar Velho (Portugal), Mladec (Czech Republic) and Pestera cu Oase (Romania) remains, among others, have abounded in the literature. Yet, most anthropologists have been, and remain, deeply skeptical.

I have myself – in the past – toyed with this hypothesis. But, alas, I no longer find much value in its capacity to explain the patterns we see in the fossil record. There are, to my mind, far simpler explanations for fossils of mixed form, that make more sense within the context of modern evolutionary biology.

The fossil evidence for interbreeding has been widely regarded to be too ambiguous and difficult, if not impossible, to test. It also represents an example of an ad hoc explanation.

Ian Tattersall and Jeffrey Schwartz published a paper in Proc Natl. Acad. Sci. USA in 1999 (vol. 96, pp. 7117-7119) addressing this very question, taking issue with claims of hybridization for the Lagar Velho child. Their article has become somewhat of a classic, concluding:

 …the Lagar Velho child’s skeleton is a brave and imaginative interpretation, of which it is unlikely that a majority of paleoanthropologists will consider proven. The archaeological context of Lagar Velho is that of a typical Gravettian burial, with no sign of Mousterian cultural influence, and the specimen itself lacks not only derived Neanderthal characters but any suggestion of Neanderthal morphology. The probability must thus remain that this is simply a chunky Gravettian child, a descendant of the modern invaders who had evicted the Neanderthals from Iberia several millennia earlier.

Even if the genomic evidence is correct that the ancestors of Eurasians interbred with Neanderthals, and some of them also with the Denisovans, this doesn’t prove, prima facie, any fossil to be a hybrid.

Studies of hybridisation in living primates show that the offspring fail to show a predictable pattern of physical features: some look like parent species 1, some like parent species 2, and others possess an unpredictable mix of features of both. Moreover, the signs of interbreeding disappear within a generation or two of crossing back with one of the original parent species.

So, the chances of finding a hybrid in the fossil record seem to me to be extremely remote.

I’ve spent many years looking for hominin fossils and they are near impossible to find. Really rich localities like the Cradle Caves in South Africa, Lake Turkana region in Kenya, Afar region of Ethiopia, and Atapuerca in Spain, are extremely rare.

It’s hard enough to find fossil sites, let alone ones that produce hominins, let alone ones that might contain hybrids! The odds are simply too large to consider sensibly.

Interpretations of the latest Neanderthal genome sequence published in Science in January of this year by Sriram Sankararaman and co-workers confirms this. Their work shows pretty firmly that interbreeding was likely to have been between distinct species: that is, between Homo neanderthalensis and Homo sapiens. Not simply populations within a species.

Supporters of all four models proposed to explain our evolution –Multiregionalism, Assimilation, Out-of-Africa with some interbreeding, and Out-of-Africa replacement – have all claimed their models to be supported by the new evidence for interbreeding. Some have even modified their ideas following the genomic revelations.

I’ve only one thing to say here: balderdash! It simply can’t be the case that all four, mutually exclusive, models can be supported by the same dataset. If they are, then the data for interbreeding are completely meaningless!

In science, strong hypothesis make very specific and testable predictions. This also makes them, in principle, easier to refute. The new Neanderthal evidence is very specific, and it simply can’t be interpreted as supporting all four ideas.