Devangshu Datta: The missing links of evolution

Recent breakthroughs strengthen the Great Ape Project's case of explaining the divergence in the evolutionary tracks

In “The Great Ape Project”, Richard Dawkins outlined a thought experiment. Imagine that a modern woman holding the hand of her mother, who in turn holds her mother’s hand and so on, in a line of ancestors going all the way back to the primeval. Mitochondrial DNA makes it possible to trace maternal lines back with certainty, hence the gender-bias to the thought-experiment.

Each woman in that imaginary line resembles her parent, and her daughter, and her grandparent, and would obviously be of the same species as them. But when we compare individuals with large gaps between generations, we see that the resemblances between distant ancestors and their descendants reduce dramatically.

 

Over long periods of elapsed time, we see a change in species characterised not only by obvious markers such as more hair and smaller skulls as we go back in time, but also by the acid test of an inability to interbreed. Eventually, way back in time, our ancestors are holding fins rather than hands, and our proto-ancestor is a gill-breathing fish.

However, much later than that beginning, just about 200 kilometres “back in time”, one of those human ancestors is seen to be holding the hand of another daughter, who is, in turn, holding the hand of her daughter, and so on. This forms a line parallel to the humans and it leads to the modern chimpanzee. Those two daughters were of the same species but their descendants evolved in very different ways.

Dawkin wished to make the point that the great apes and human beings were closely related and shared over 97 per cent of their DNA. The reason the resemblance isn’t more obvious is that the intermediate species (many “missing links”, rather than the fabled singular one) went extinct. We cannot interbreed with chimpanzees but many of our not-so-distant ancestors could, and definitely did.

This powerful analogy simplifies our understanding of how homo sapiens sapiens (HSS is what we call ourselves — it roughly translates as “wise, wise man”) evolved from the fish that crawled out onto the mudflats of Africa. For many years, it was thought that HSS was the only survivor out of several closely-related species of the genus homo.

In fact, until recently, we named ourselves homo sapiens in the taxonomy. The second sapiens was added for emphasis, and out of political correctness, when it became apparent that the extinct species of Neanderthals (Homo Sapiens Neanderthalis) were also quite bright. It was assumed that HSS had probably helped wipe out the other sub-species as it assumed dominance.

Recent breakthroughs in fossil collection and genome sequencing suggest a further modification of that theory. HSS certainly did contribute to the extinction of the Neanderthals and some of the means employed would have been violent. But it also interbred with them and, thus, modern HSS is a hybrid, with a recognisable set of Neanderthals sub-species genes still visible in the pool.

As far as we can make out, primates started walking erect somewhere between two million and three million years ago, somewhere in Africa. They developed larger brains and their eating habits changed from being primarily vegetarian, to being omnivorous. Various sub-species that could interbreed with each other migrated out of Africa around 100,000 years ago and these colonised the other landmasses.

Neanderthal fossils have been found all over the Eurasian landmass. Sometime between 25,000 and 50,000 years ago, the Neanderthals seem to have gone extinct, going by the fossil record. This occurred during the last Ice Age and it was assumed that they had been driven out of their shrinking habitats by competition from HSS. However, somewhere between one and four per cent of all genes in the modern human pool consist of Neanderthal genes. This proves interbreeding took place and the Neanderthal was genuinely homo sapiens.

In 2008, the finger bone of a Neanderthal sub-group was discovered in the Denisova Caves of Siberia by members of the Russian Academy of Sciences. By 2010, draft genome sequences had been released by the Max Planck Institute of Evolutionary Biology. The Denisovan was a Neanderthal or at least, very closely related to the Neanderthal.

A couple of days ago, a research team from the Max Planck Institute decoded the entire genome sequence of the Denisovan and placed it on the Internet. They used new techniques to manage this complete sequence from less than 10 milligrammes of bone material. This is the first complete genome sequence of an extinct human species and it means a great leap forward in understanding.

Once those techniques are applied to other fossils and once other scientists start comparing that genome sequence with modern human groups, we’re likely to develop a more nuanced understanding of genus homo and of the proto-history of our race, its evolution and migratory patterns. Unravelling that story involves forensic sleuthing involving a combination of multiple technologies, ranging from carbon dating to DNA-sequencing.

The Great Ape Project originated with a group of scientist-philosophers. It advocates a UN declaration of rights for chimps, gorillas, orangutans and bonobos, offering protection from torture, right to life, liberty, and so on, since they are rational beings who are our closest relatives.

The latest breakthrough strengthens the Great Ape Project’s argument. It will lead to a better understanding of the missing links that explain the divergence in the evolutionary tracks. It is yet another nail in the coffin of the religious sceptics who refuse to accept Evolution because it contradicts their faith.