The Journey of Man: A Genetic Odyssey (2 page)

The Australian Aborigines maintain their sense of connection to their ancestors and their homeland through a musical story—something Bruce Chatwin and others have called a ‘songline’. These songlines reflect the actual journey taken by their ancestors during the Dreamtime, a period in the distant past, before collective memory. In a sense, this is precisely what we are trying to do with our studies of DNA—resurrect a global songline for everyone alive today, describing how they reached their current location and what the journey was like. As secular Westerners we have lost our traditional songlines to a greater extent than other peoples around the world, so it is perhaps appropriate that Western science has developed the methods for rediscovering them. However, our research does not take place in a vacuum, and science can sometimes run roughshod over cultural beliefs. I would hope that this book might be a small step towards changing the field into what it really is—a collaborative effort between people around the world who are interested in their shared history.

So, with that as an overview, let’s start our genetic excavation. The past awaits …

Creation myths can be found at the core of all religions. Most seek to answer the child’s question ‘where do we come from?’ – to explain our existence and our place in the world in a succinct way. But while they may attempt to explain how we originated, creation myths fail to account for the spectrum of cultures, shapes, sizes and colours we see when we look at people around the world. Why do we look so different from each other, and how did we come to inhabit such far-flung places?

Herodotus, the fifth-century
BC
Greek historian, provided posterity with far more than a description of the Greco-Persian wars. He also gave us our first clear descriptions of human diversity, viewed through an idiosyncratic classical lens. We learn of the dark and mysterious Libyans, the barbaric man-eating Androphagi of the Russian north, and hear descriptions of people who seem to resemble the Turks and Mongolians. Herodotus relates fanciful tales of griffins guarding precious hoards in the mountains of Asia, and we are treated to exotic descriptions of tribes in northern India who collect gold from the burrows of ants. Overall, it is a tour de force – the first ethnographic treatise in Western literature and, despite its obvious flaws, a valuable snapshot of the known world at that time.

If we were to assume the role of a naïve modern-day Herodotus and fly an equatorial route around the world, the diversity of people and
places would be astounding. Imagine for a moment being on a plane above the Atlantic Ocean at the very centre of the Cartesian globe, 0° longitude, 0° latitude – about 1,000 km west of Libreville, Gabon, in west-central Africa. If we imagine the plane flying east, and allow ourselves the science-fiction trick of being able to scan the ground from our vantage point in the sky, we will get a small sample of humanity’s diversity.

The first people we encounter are Africans – specifically, central Africans, speaking Bantu languages. They have very dark skin, and live primarily in small villages hacked from the forest. As we move further east, we still see dark-skinned people, but these look somewhat different. They are the tall, thin Nilotic peoples of east Africa – some of the tallest on earth. They live on grassy savannahs, and are almost completely dependent on their cattle for survival. Scattered in amongst these groups are people who speak yet another language – one which is as different from Nilotic and Bantu as they are from each other, even though they live close by – the Hadza.

As we continue east we encounter a huge body of water – so vast that it is impossible to see across it, and it seems an eternity before we reach an archipelago known as the Maldives. The people here seem quite different from those we saw in Africa, and speak yet another language. Their skin is dark, like that of the Africans, but their faces are different – nose shape, hair type and other minor details. They are clearly related to the Africans, but differ in obvious ways.

As we continue on our journey – above the same enormous body of water – we see a large island rising up ahead of us. We have reached Sumatra, and here we encounter yet another type of human, somewhat smaller than the Africans and peoples of the Maldives, with yet another facial appearance – very straight hair, lighter skin and a thicker layer of skin above the eyes. Further east, passing countless other islands, we again encounter people with very dark skin, known as Melanesians. They are unlike the Africans in many other ways, so is their dark skin a characteristic that evolved in this region? Or is it indicative of a close connection with Africa?

Next we encounter the Polynesians, living on small coral atolls separated by thousands of miles of open ocean. They appear to be somewhat similar to the Sumatrans encountered before but, as always
seems to be the case, they are different. The biggest question is why they are living in such remote locations – how did they get there?

Continuing on our route, we encounter the coast of Ecuador, in western South America. In the capital, Quito, we find an odd mix of people. There seem to be two main types: those who in some respects resemble the peoples of the Maldives, but with lighter skin, and those who in many ways resemble the Sumatrans and Polynesians. It seems odd to find such divergent types of humanity living in the same place, since the other locations we have visited tended to be more homogeneous. Why is Ecuador different? A disparate mix of people is found further east on the continent, where on the north-eastern coast of Brazil we encounter Africans again – but living far from Africa! During the long journey back to our starting point we ponder the tapestry we have just seen, and try to formulate an explanation for the pattern of diversity.

Our short tour of the world was a kind of thought experiment, where we imagine what it must have been like to encounter things as people may have done a few hundred years ago, during the first European ‘voyages of discovery’. By assuming the guise of ignorance, we can ask simple questions that seem trivial to us today, given our knowledge of history. The interesting thing about this thought experiment is that, until very recently – excepting the Africans and Europeans encountered in South America – there was no ready explanation for the patterns we saw.

On 30 June 1860 an angry cleric named Samuel Wilberforce mounted the stage at Oxford University’s Museum Library. He was primed for a fight – not just for himself, but for something far more important: his worldview. Wilberforce felt that he was fighting for the future of Christianity. The venue was a formal debate on the place of man in nature, a field of enquiry until recently limited to philosophers and the church. The good bishop, taking scripture at its most literal, believed the world to be around 6,000 years old, created by the hand of God on 23 October 4004
BC
, a date obtained by counting back through
the genealogy described in the Bible. In his speech he asked a pointed question – one that was on the minds of many in the audience. Was it really possible that he could be related to a monkey? It sounded so preposterous!

Wilberforce was a polished speaker, and to many in the audience his argument was persuasive. But while he held his own in the library that day, in the long run he was destined to be trounced. And, foreshadowing a significant change in the way we viewed our place in the world, the dragon slayers were not philosophers or clergymen but professional scientists. Joseph Hooker and Thomas Henry Huxley, both Victorians par-excellence, were strong supporters of Charles Darwin’s new theory of evolution by natural selection. Huxley, lecturer in biology at the London School of Mines, later became better known as ‘Darwin’s Bulldog’. Hooker was an accomplished botanist and assistant director of the Royal Botanical Gardens at Kew. When they rose at the end of Wilberforce’s lecture to refute his emotional arguments, they were sounding a death-knell to the old views on human origins. Science was leading the way into a brave new world.

The debate between Wilberforce, Hooker and Huxley served not merely to reinforce the public’s acceptance of evolution – most educated people had already come to see the world in an evolutionary context – but rather to realign humanity’s place in it. When we viewed ourselves as the divine creation of an omnipotent being, we could easily justify our isolation from the rest of the living world. Masters, conquerors, perhaps favoured children – but different.

Darwin’s insight had changed all of that. This dyspeptic near-recluse had, with a few strokes of his pen (and some twenty years of dabbling with pigeons and barnacles), demoted humanity from divine creation to a product of biological tinkering. And the odd thing is that he hadn’t even set out to do this. Darwin, the scion of a wealthy Victorian family (his grandfather was Josiah Wedgwood, his father was a wealthy physician, and Darwin himself spent part of each day looking after his investments), had no intention of rocking the boat when he set out on his voyage of discovery aboard the
Beagle
in 1831. He was certainly looking for adventure, and needed something to stave off the looming inevitability of a staid country parsonage – the logical career choice
for a Cambridge graduate of that era. But he was looking for something else as well.

As was the case with many Victorians, Darwin had developed a keen interest in science during his childhood. While he had the usual chemistry accidents, especially with his older brother Erasmus – with whom he once destroyed a garden shed-cum-laboratory when an experiment went explosively awry – Darwin’s interests were primarily of the outdoor variety. He was inordinately fond of beetles (he once wrote in a letter of ‘pining’ for a like-minded beetle fancier), and spent many hours in the field scavenging for exotic specimens. But it was his interest in geology, developed while he was a student at Cambridge, that was to have the greatest impact on his future work.

Geology was undergoing a revolution in the early nineteenth century – one which was calling into question our whole understanding of history, as handed down in the Bible. Darwin was an adherent of a school of thought that became known as uniformitarianism, first formulated by Charles Lyell. Lyell believed that the forces and materials found in the world today had always behaved in essentially the same way – even in the distant past. Diametrically opposed to the uniformitarian school were the catastrophists – led by major scholars such as Louis Agassiz, a Swiss transplant to America who founded Harvard University’s Museum of Natural History. The catastrophists believed that the earth went through long periods of stasis when nothing much happened, but that occasionally all hell would break loose. This could take the form of a biblical flood, or an ice age, or a massive upheaval in the earth’s crust. All major changes – in organisms as well as the planet itself – were driven by these freak events. The distribution of the world’s plant and animal species was due to a series of catastrophic events during their history.

The problem with catastrophism was that it relied too much on odd happenings to be of any use – there were rather a lot of changes that seemed to have occurred without any drastic catalysts. If change could occur without invoking a major causal event, then why was it necessary to invoke them at all? Why not simply assume that the earth is constantly changing at a very gradual rate, and that over long periods of time these incremental steps produce significant results? It seemed so much easier to reconcile with the actual data, said Lyell.

All of this was percolating in young Darwin’s mind when he set out aboard HMS
Beagle
, engaged as a ‘gentleman companion’ for Captain FitzRoy. This unusual position had to do with Victorian social customs, in that the Captain was considered to be of too high a social class to mix with the crew. There was, in fact, an official naturalist on board the ship – the ship’s surgeon – but he ended up leaving the voyage in Brazil after a falling out with FitzRoy. At any rate, Darwin was the
de facto
naturalist on the journey, and his lack of official status as such allowed him enormous leeway in pursuing his own studies.

His journal from the five-year journey,
The Voyage of the Beagle
, is a classic of nineteenth-century travel literature. During the trip, Darwin made several major discoveries, including finding a reasonable explanation for why coral atolls are round (it has to do with receding volcanoes) and deciding that the Tahitians were very attractive people indeed. The most important – his initial insight into the action of natural selection, and its role in the origin and evolution of species – has been examined so often that it isn’t necessary to reiterate here. Suffice to say, Huxley and Wilberforce would never have faced off in 1860, and you wouldn’t be reading this book, if Darwin hadn’t recognized natural selection as the driving force of evolution.

It is one of Darwin’s other subjects, discernible even in this, his earliest major work, which interests us here. It is a subject which is dealt with more subtly than his discussion of biological evolution, presaging his hesitation nearly thirty years later to include a direct discussion of it in
The Origin of Species
. The subject is humanity. Or rather, the diverse array of humanity encountered through the lens of a Victorian scientist with an urge to explain the patterns he saw. Why were people around the world so different from each other?

The
Beagle
set sail from Devonport, near Plymouth, on 27 December 1831, calling at the Cape Verde Islands, Brazil, Argentina, Tierra del Fuego, Chile, Ecuador, the Galapagos, Tahiti, New Zealand, Australia, Mauritius and Brazil (again) before returning home on 2 October 1836. Travelling on such a grand, circuitous route, Darwin had a chance to encounter many different groups of people first-hand. He explored Brazil, witnessed the gauchos of Argentina in action on the pampas and trekked into the Andes with Chilean guides. Perhaps
the most distinctive people he encountered, though, were the native inhabitants of Tierra del Fuego.