Human evolution : how we talk, and the power of inference

Much biomedical research bores me. All too often it is either dull risk factorology (i.e. most epidemiology) or, as for so much cell biology and biochemistry, endless chasing of one molecule causing another molecule to change and, in turn, alter yet another molecule. The cascade goes on: there are lots of molecules after all. It was really so much more fun when the whole of cancer genetics was about ras mutations. Fun, but wrong and incomplete. At the same time, the real intellectual ferment in health care is in the clinic —except that many of the changes are for the worse, and tradional natural science often does not provide the right sort of rationality with which to understand what is going on.

There are however exceptions. If you look at the 15-20 years I spent studying skin cancer and human pigmentation using genetic approaches, I think I discovered little of immediate or even short term importance for the treatment of disease. Grant applications of course played to the likely clinical relevance, but with hindsight and the objectivity that science and academia are supposed to champion, the claims were to put it mildly, exaggerated. What was fun, and I think of modest import, was the work on MC1R and human evolution.  In the grant scheme of things our work may have broader importance but, using the taxi driver test as my assay (the conversation that happens whether you want it to or not), I have yet to find a human being who is not fascinated by human evolution and the amazing power of modern genetics to unlock our past. Some people have literally been in this field for more than 60 years, others like me have just been close to the sidelines, but I still have to pinch myself to marvel how a few decades after Watson and Crick, and Sanger (and a bunch of  clever engineers who build the sequencing machines), that we can use sequence data as a camera that sees into how human lived and died hundreds of thousands of years ago.

Biologists I suspect always envy the power of inference afforded to physicists —it is dark at night, therefore the universe is expanding (Oblers paradox) as an example. But approaching this for me was the following phrase from a paper in PNAS by  Henn, Cavalli-Sforza and Feldman.

A recent analysis of phonemic diversity in 504 worldwide languages shows that this diversity exhibits the same serial founder effect discussed earlier for genetic variation, namely a loss of phonemic diversity proportional to distance from Africa . Moreover, within Africa, the greatest diversity is in the southern central region. Although the regression of phonemic diversity on distance from Africa is not as strong as seen with DNA polymorphisms, this finding nevertheless suggests that the genetic and linguistic expansion from Africa could have been part of the same process.

I am not the best person to explain this, but essentially we know there is greater genetic diversity in African populations than in those populations ‘Out of Africa’. Cavalli-Sforza and others have shown however that there are strong parallels between genes and language. Here they are showing that just as the amount of genetic diversity drops as distance from Africa increases, so does the variation in the sounds human utter. Can you really believe that one could have imagined this a century ago? Using Mendel’s ideas about peas, and Darwinism, to track how words were uttered a hundred thousand years ago.

Post by Jonathan Rees

Clinical academic and skin watcher at the University of Edinburgh

Comments are closed.