The future of sapiens (perhaps)

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Anatomically speaking, contemporary humans appeared 130,000 to 160,000 years ago in Africa and began migrating out of Africa between 50,000 and 100,000 years ago; in Australia 50,000 years ago; in the New World 13,500 years ago; in Polynesia 1,500 years ago. In short, in the space of 100,000 years, sapiens colonized 70% of the planet, a feat that outstrips the colonizations carried out by other mammals by a factor of 10.

There are 6 billion of us, so the number of hominins (since 5 million years ago) who have lived would be of the order of 150 billion individuals. At a mutation rate of 7 × ^10-5 per gene and per person, we should be seeing significant genetic diversity today. This is not the case, however, and implies that we are in fact derived from a small original population (around 10,000 individuals). Add to this the small number of genes we have, and it's clear that questions of regulation outweigh those of the quantity or nature of genes.

The question is often asked whether sapiens continues to evolve. The most spontaneous answer is no, which puts the onus on cultural and technical adaptation, on which I would have liked to close this year's lecture. But in fact, genetic evolution continues too. For example, the deletion of CCR5, a cytokine receptor, is increasing in frequency, no doubt or perhaps because it leads to resistance to HIV. In fact, infectious diseases are a powerful selective force in human evolution.

The debate on evolution, as far as the human lineage is concerned, has taken place in the terms posed by the following equation: (i) We have few genes (# 25,000), and they are, for the most part (# 99%), identical to those of the chimpanzee. (ii) Evolution has been very rapid, since the ancestor we share with the chimpanzee is thought to have lived approximately 7 million years ago, while the human species is barely 200,000 years old, a mere trifle in the long history of life (3.5 billion years).

The conclusion is obvious. This 1% involves sequences of considerable qualitative importance. What matters most in development, and most probably in evolution too, are developmental genes. What's more, the changes at the origin of major phenotypic modifications are not to be found solely, or even primarily, in the coding sequences themselves, but in the elements regulating the expression of these genes.

From there, the lecture continued with a description of the main levels of regulation that can explain the uniqueness of sapiens. Let's not forget that 1.23% of differences among 2.4 billion bases is still 30 million nucleotides, to which must be added insertions and deletions (INDEL), not included in these mutation analyses, which account for a further 3%. Not to mention genes that are commonly duplicated or lost. Between humans and chimpanzees, the number of copies differs by 6.4%. These events could therefore have played a fairly important role in the evolution of primates - and not just primates - more important in any case than point mutations.

It's impossible to go into the details of the lecture, but it's interesting to note that all recent studies associate the evolution of sapiens with the rapid evolution of the expression of genes involved in functions as diverse as cell proliferation in the nervous system, neuronal morphogenesis, synaptic activity and energy metabolism. Finally, we concluded with a number of point mutations, including that of the FoxP2 gene, which recent studies suggest are involved in the emergence in sapiens and neanderthalis of the motor capabilities - at least those - of articulated language.