The genius of Charles Darwin shows us that we have so much more in common, as human beings, than we have things that separate us. Once you’ve peeled away the superficial markers of “identity” – like skin colour, shape of nose or mouth, weft of hair – you find we’re all built of the same stuff. Our bodies are the result of about seven million years of evolutionary process that took place right here in Africa.

The “deep roots” of our anatomy evolved in Africa, before colonisation of the rest of the world began. It is only in very recent times, possibly the past 50 000 years, that superficial differences like hair colour and eye shape began to creep in as groups of humans settled into different parts of the globe and began to develop common features in isolation from other groups of humans.

“Our shared species features originated here in Arica,” anthropologist Prof Chris Stringer from the London’s Natural History Museum said during the Nelson Mandela Science Lecture at the University of the Western Cape, on Wednesday. The lecture marked the 150th year since the publication of Darwin’s groundbreaking work, On the Origin of Species by Means of Natural Selection.

“When we look around the room we can see we’ve all got higher, rounded skulls, small faces, chins on the lower jaw. These are the common shared features of humanity that evolved here in Africa. But (people) also come in different sizes, shapes and colours. These individual, regional differences, the so-called ‘racial’ differences… were superimposed on that original, modern template more recently.”

Darwin punted the idea that humans evolved in Africa decades before there was even any fossil evidence to support the theory. But hominid remains found during the past century show how visionary – and accurate – his thinking was.

His argument for our African origins was based on comparing our anatomy with that of the great apes. He noted that our body structure is closest to that of Africa’s apes, namely gorillas and chimps, rather than the apes of South-East Asia, such as orang-utans. So it followed, he reasoned, that our ancestors must have evolved here from a close common ancestor of Africa’s apes.

The first early human-like fossils were found outside of Africa – such as the Neanderthals in Europe and “erect ape man”, Homo erectus, in Java – leading Darwin’s contemporaries to argue for the origin of humans in Asia. But since then mounting evidence in fossil finds shows that Africa is the only continent where there is a continuity of evolution from the earliest hominids through to modern humans.

Africa has produced the sequence of transitional fossils which shows the transformation of ancient ape-like ancestor into humans over the course of seven million years. Skeletal remains illustrate the shift from a four-legged, tree-scrambling shape to an upright, walking gait which was energy efficient and freed up the hands to begin manipulating things.

The sharp, interlocking canine teeth that are still present in the great apes, shrink as humans become more modern, possibly suggesting a change to an omnivorous diet (our canines mean we can grind our food in a rotary way, which chimps can’t do).

“Darwin (also) theorised that as our ancestors started using tools, their canine teeth didn’t need to be large anymore. Gorillas and chimps use their canine teeth in aggressive encounters, often just baring them at each other to make threats. Whereas us humans, as Darwin envisioned, have other things we can use to threaten people and defend ourselves.”

The brain and skull casing begin to swell in size so that, today, our brains are three to four times the size of our nearest living relative, the chimpanzee. This change could well be the result of a shift from a vegetarian diet, which for other apes is an energy-intensive diet requiring many hours for  foraging and still more effort to digest, to a diet including meat which gave extra calories for the energy-hungry brain. 

All of these – the large, complex brain; walking upright which freed our hands for other tasks; smaller canines – indicate a link with the development and use of tools, something which allows us to become the industrious creatures we are today. These features are common to every human across the globe, regardless of external veneer, and evolved here in Africa before our great migration out across the globe.

But Darwin was less confident about society’s readiness to hear about this idea, than he was about his theories. So he held back from publishing On the Origin of Species for many years. And even then, he skirted around the idea that humans had descended from a common ancestor shared by today’s great apes (we’re not evolved from monkeys, as is the popular misconception).

It was only in 1871 that he tackled the issue in The Descent of Man, in which he laid it out clearly our links to the great apes. This thinking forced a seismic shift in the modern world, tearing a crack in many different creation myths that had had a few thousand years to build up a head of steam. Darwin showed not only how natural forces explain the origins of life, but that humans are but one small part of an abundant bush of life; that we are not above nature or having dominion over it, but that we are just one part of an indifferent food chain.

There’s one beautiful truth about this story that is often overlooked in the prevailing and overblown controversy that still lingers a century and a half later – the fact that every human being walking this Earth is part of the same, close-knit family. That we all started out as black Africans, but those of our ancestors who trekked out of the mother continent to colonise the rest of the world had our exteriors tweaked over thousands of years so that we ended up looking a bit different to our brothers and sisters back home.

So what drove the differentiation of our features so recently in our history? Darwin’s view was that natural selection could explain variation in skin colour, as the epidermis evolved different degrees of protection depending on how much sun a group was exposed to over many generations. But he believed that sexual or cultural selection explained the evolution of features such as differences in eye shape or hair colour, shape of nose, and the likes.

“Different groups (around the globe) developed different standards of attractiveness and beauty and in that way they evolved differently to other (groups).”

How quickly could this kind of superficial diversification have begun to shape the human exterior? Stringer said that a combination of natural selection, sexual selection, founder effect and genetic drift could easily have brought about this kind of variation in modern human diversity in less than 100 000 years.

Stringer made one other humbling point – that modern humans haven’t reached some pinnacle in the evolutionary process, as is often misunderstood in the many illustrations of our progressive development showing anatomical change from our hominid ancestors over the past few million years.

“We’re just at one part of an evolutionary path. We could even be going in a bad direction.”

Of all the human-like ancestors whose fossil remains have been found – both in Africa (the Australopithecines, amongst others), Europe (the Neanderthals) and Asia (Homo erectus) – all of them have dwindled into extinction. Home sapiens, the so-called “wise humans”, is the only remaining human-like line left on the planet.

“We’ve been lucky. I don’t think there’s anything necessarily very special about modern humans. If we changed some of the climate parameters in Africa (during the past few million years), for instance, modern humans may not have evolved. “

But with the threat that human-caused climate change now poses to the future of modern civilisation, Stringer said our future evolution isn’t assured.

“Our species might not even get a chance to evolve unless we address the issue of what we’re doing to the Earth at the moment, with this uncontrolled experiment that we’re running with the climate system.”

Some thinkers, including the scientist-author James Lovelock, argue that if the worst projections of climate change come to pass, humanity’s numbers will plummet as the resulting environmental change undermines food and water supplies, spreads disease, causes sea levels to swamp highly populated coastlines and pushes communities into conflict. Only a small number of humans will make it through a tight bottleneck – and if these are able to survive, they will become the founding community for future generations of humanity.

How many individuals would need to survive in order to allow for a genetically viable human population on the other side of the bottleneck?

The “seed” population of early humans who left Africa and spread to populate the rest of the world could have been about 10 000 individuals, but maybe as few as only 400. Just imagine – if only 400 individuals were left to repopulate the world after a calamity like climate change, who they’d be and what they’d look like 100 000 years from now?

The Nelson Mandela Science Lecture was presented as a partnership project between the Africa Genome Education Institute and sanctioned by the Nelson Mandela Foundation. The 2009 lecture was held jointly with the Darwin200 series of lectures, a partnership project of the Africa Genome Education Institute (AGEI) and the Division of Human Genetics at the University of Cape Town.

Leonie Joubert is a freelance science journalist, author and columnist. She was the 2007 Ruth First Fellow, was listed in the Mail & Guardian's "200 Young South Africans you must take to Lunch" and was recently named the SAB Environmental Journalist of the Year 2009 (print and internet category). This article was written on behalf of the AGEI.