The Incredible Human Journey (17 page)

Abandoning the hunt, we settled for a bit of target practice. I had a go at using the blowpipe and found it to be very accurate even in inexperienced hands: the length of the blowpipe made it easy to sight a target, and even I could hit a tree trunk some 10m away with it. This was obviously very different from being able to hit a moving quarry high in a tree-top, but I felt proud of my achievement, and I was impressed with this simple but effective tool. Blowpipes were actually a fairly recent introduction: until 1910, the Lanoh had hunted using bows and arrows, but they picked up the use of blowpipes from a neighbouring tribe, perhaps as they moved deeper into the rainforest. Blowpipes have a range of good accuracy up to about 35m, compared with 100m for bow and arrow.
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Archery is effective in more open woodland, but the blowpipe is even better suited to hunting in dense forest. The adoption of the blowpipe by the Lanoh represented a very recent example of human cultural adaptability to a changing environment.

When I returned from my trip into the forest, preparations were under way for a
sewang
: a celebratory dance. Stephen had finished his sampling and we sat down in the shade. Alias opened fresh coconuts with a machete for us and we ate a snack of roasted tapioca; for a while I couldn’t work out what it reminded me of, then it came to me: roasted chestnuts.

As darkness fell, we made our way over to the
balai sewang
where people were just beginning to gather. The four musicians struck up a melodic beat on bamboo instruments, and the dancing started. Between being alternately dragged to the floor to dance, we talked about the antiquity of the Lanoh, Stephen’s work on genetics in South-East Asia, and ideas about anatomically modern human origins and migrations.

Genetic analyses in South-East Asia had already revealed some surprising results. Many East Asians possess distinctive features: an epicanthic fold over the inner corner of the eye, a ‘single’ upper eyelid, facial flatness and shovel-shaped incisors. These features are more strongly pronounced in north-eastern Asians, so the traditional view was that people and genes had flowed from north to south in East Asia.
⁷
However, some anatomical studies had suggested that the flow was in the opposite direction, and this was backed up by Stephen’s work on mitochondrial DNA lineages in Malaysia. The general Malay population didn’t appear genetically to be part of a southern expansion of north-east Asians at all; in fact, the northern populations in China, Taiwan and Japan appeared to be descendants of South-East Asians.
⁸

But the majority Malay population were not direct descendants of the original South-East Asians. Instead, the most ancient genetic lineages in Malaysia belonged to Semang tribes. Their genes recorded a near-extinction of the Semang, with a loss of genetic diversity, but the surviving lineages could still be traced back to around 60,000 years ago.
⁹
As I had told Alias, this meant that the Semang were ‘Orang Asli’ in the true sense: they were ‘original people’. They represented relics of the original migration, and their ancestors were the first colonisers of this part of the world. Of the six distinct Semang groups, Stephen had already sampled four – but not the Lanoh tribe.

So another twig was about to be added to the South-East Asian part of the mtDNA tree. It may sound a little like genetic stamp collecting, gathering these populations from around the world into a bulging DNA album, but every new population sampled adds more detail to the genetic tree, more twigs. Not only that, but the dates of the branch points become even clearer, so the overall structure of the tree, from root to branch to twig, becomes more obvious, and the dating of branch points more secure. ‘Looking at the Lanoh is, in the first instance, a way of testing that they are descendants of the first settlers in this area. But it’s also very important to increase the number of sample points, in order to improve the dating and get a better picture from the genetics as to the date of their first arrival here,’ explained Stephen.

Stephen also believed that skin colour offered clues about past migrations. The colour of our skin is perhaps the most obvious way in which we all vary from each other. And at the moment it seems to be the only variation that is completely explicable in terms of adaptation to environment. Skin colour varies according to latitude and levels of ultraviolet radiation: the closer to the equator you and your ancestors lived, the darker your skin. The further away from the equator you get, the paler indigenous people become.
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11
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12

Dark skin is rich in the pigment melanin, protecting deeper layers of skin from sunburn and skin cancer. In sunny places, it seems reasonable to assume that natural selection would act to conserve genes that make skin dark, as any mutations producing pale skin would be a disadvantage. So the ‘original’ skin colour of modern humans was probably quite dark. But in populations moving a long way from the equator, to the cloudier, northern parts of Asia and in Europe, the selection pressure for dark skin would have diminished. And ‘pale’ mutations could therefore occur without being weeded out. It may be that there was even positive selection for paler skin in northern climes. We acquire vitamin D in our diets, but we also make it in our skin, in the presence of sunlight. In places with strong sunlight, dark skin is still able to manufacture sufficient amounts of vitamin D. But as people moved northwards, skin damage from sunlight became less of a pressing issue, while dark skin would have limited the skin’s ability to produce enough vitamin D.

Vitamin D is important in calcium metabolism: deficiency of this vitamin leads to rickets, where bones grow soft and bendy. Long bones become crooked and the pelvis collapses in on itself, making childbirth impossible in extreme cases. So natural selection may have acted to make European skin paler: random mutations that tinkered with the production of melanin in skin cells may have offered an
advantage
to sun-deprived Europeans. And so, gradually, the population would have changed from brown to white. The same thing happened to the populations of northern Asia, and some details of the genes responsible are now known. It seems that a different set of genes mutated in Europe and in Asia, but produced a similar paleness of skin in each place: an example of convergent evolution.
¹²

The Lanoh have very dark skin compared with most Malaysians. But, at just 3 degrees north of the equator, it was the Lanoh that actually have the ‘right’ level of skin colour to protect them from the tropical sun. Stephen believed that today’s majority Malay population represented a much later incursion of people from further north in Indo-China, people with much paler skin than the indigenous Malay tribes, perhaps around the time of the LGM. Selective changes take a significant amount of time to occur. ‘Twenty thousand years is not long in this context,’ Stephen said; hence the too-pale-for-the-tropics skin colour of most Malaysians.

Following all this discussion about skin colour, I also wondered about the effects of sexual selection, and perception of attractiveness. In both India and Malaysia I had noticed that the people shown on billboard advertisements and posters all had
much
paler skin than the real people I had seen: those aspirational creatures were youthful, glamorous and so pale as to be almost white. Of course, back home in Britain the images of ‘white’ beauty we are presented with are much more tanned than the majority of Anglo-Saxons you see around the place. In Malaysia you can buy moisturiser containing whitening agents; in the UK, we tend to buy moisturisers with tanning agents. We all seem rather ungratefully unsatisfied with the skin colours that evolution has fitted to our climates for us. But Stephen thought that aspiration to a particular skin colour might be driven by more than just a desire to look ‘different’. In an ethnically mixed population, skin colour was tied to perceptions of social status or wealth, related to cultural and economic history. So skin colour could act as a marker of exclusivity. Stephen also suggested that if human skin colour didn’t vary, we’d have found something else on which to base exclusive behaviour.

Returning to the main theme of Stephen’s genetic work, everything he and other geneticists had discovered seemed to point to an origin of modern humans in Africa. Stephen talked about his particular niche within the discipline as ‘genetic phylogeography’: he was building family trees based on the information contained in genes, but then relating these constructs to geography.

‘Phylogeography is different from traditional population genetics because, instead of comparing mixes of genes in different populations, you follow individual genes, and find where the gene lines go,’ explained Stephen. Rather poetically, he described the branching genetic lineages as ivy draped across a map of the world, with the newest branches standing out as paler green shoots from the darker green main stems. ‘In phylogeography, we know when we’ve got new growth because there are new genetic mutations.’

The roots of the ivy were firmly planted in Africa, and a single branch, representing L3, emerged to give rise to all the secondary branches outside Africa, starting with the M and N branches: today, every non-African in the world belongs to either the M or N lineage. There are numerous, ancient, primary branches of M in India, suggesting that the M haplogroup probably arose in India.
¹³
But in eastern India, there was also a proliferation of younger branches of M, which Stephen thought could be related to a recovery of populations after the Toba super-eruption.

Toba again – in this part of the world it seemed you couldn’t go far without coming across echoes of this ancient disaster. I didn’t get to visit the site, but Stephen told me about Kota Tampan. It’s a Palaeolithic site in the Lenggong Valley with stone tools dating back to the Toba super-eruption, embedded in the ash layer. These stone tools are quite crude pebble tools, worked only on one side, similar to those found with much more archaic humans. But the Malaysian archaeologists found the same sort of tools associated with the fossil remains of a modern human, ‘Perak Man’, dated to around 10,000 years ago, and so they argued that the older tools were probably made by anatomically modern humans as well. It’s intriguing – could modern humans really have got as far as
Malaysia
by the time Toba erupted, 74,000 years ago? Stephen certainly thought so. But unless actual fossil remains of anatomically modern humans dating back to the time of Toba are found in South-East Asia, the jury will have to remain out.
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Our conversation came back around to the Semang – how did they fit on to that branching phylogeographic ivy? Unique mutations in the Semang mtDNA lineages marked out their branches as pale green ‘new growth’ on the stem. But Stephen pointed out that it was the length of these branches that was really significant. While the Semang branches were unique and specific to this part of the world, they were also extremely early branches, springing straight off the original M and N stems. This suggested that the ancestors of the Semang had been part of the rapidly moving vanguard of colonisers spreading around the coast of the Indian Ocean. In fact, that’s what the branches look like all along this coastal route. The tree looks ‘rake-like’: the M and N stems spread along the coast really quickly: too quickly to accumulate new mutations, staying ‘dark green’. It’s only in the branches springing off those long M and N stems that ‘pale green’ shoots – new mutations in specific geographic locations – appear.

We talked about more general issues of human origins and how to define the human species. Stephen was certainly a supporter of the recent African origin. However, although he was very clear about the absence of any genetic indication of mixing between anatomically modern and archaic humans (such as
Homo erectus
and Neanderthals), he was also careful to say that this wasn’t evidence of absence. In other words, modern and archaic humans could possibly have met and reproduced, but, in which case, the offspring were sterile or the lineages produced died out, and aren’t seen in any people in the world today (or, at least, among the steadily growing number of populations whose genes have been sampled).

The
‘phylogeographic ivy’ of mitochondrial DNA lineages, laid across a map of the world

Although Stephen was sure that modern humans had effectively replaced earlier, archaic populations, he was quite liberal about where to draw the species line. He described the first anatomically modern humans as a small band, perhaps just ‘one of the races of
Homo heidelbergensis
’, with Neanderthals as another ‘race’. So modern humans throughout the world today could be thought of as the human race that survived while the others died out. It was a thought-provoking idea, and I particularly enjoyed conversations with Stephen for just that reason. His knowledge about the genetic make-up of modern humans throughout the world indicated to him that a small group of a few thousand people, living in Africa around 190,000 years ago produced all the human populations alive today.