A life in the raw

Are humans the crowning achievement and end point of the evolutionary path that lead from the first hominid to homo sapiens? There is new evidence emerging from the study of population genetics that we are still evolving. Many of the important traits that have been under recent selection pressure relate to how we respond to a diet with an increased proportion of plants and intriguingly how we prepare our foods.

The recent finding of Hobbit man (homo floriensis) on the island of Flores has reignited the debate about whether humans are susceptible to Darwinian natural selection, or whether selection that selects favourable genes or combinations of genes has stopped, because humans have become masters of their own destiny. Some would argue that we are no longer part of nature but that we are actively modifying the global environment for short-term benefit.

Homo floriensis were tiny, a metre tall, with primitive features and a small brain. They were hunter-gatherers and very successful at that. In appearance and physique, they hark back to that distant hominid ancestor, the Australopithecus species, which gave rise to the first Homo species more than two million years ago. Their physical appearance appears to be a result of the evolutionary phenomenon of island dwarfism mirrored in their favourite prey, stegodons, a miniature form of primitive elephant.

These Hobbit men are an example of natural selection of fellow hominids, on an island, with limited resources, who drastically reduced in size over time. Yet archaeological evidence on Flores suggests these ancient miniature humans lived alongside full-size humans for at least 25,000 years. Dating techniques indicate that the most recent homo floriensis skeleton is only 13,000 years old.

But the study by University of Chicago researchers reveals that Homo sapiens 13,000 years ago were very different from homo sapiens today.

The end of the last ice age saw humans undergoing a dramatic lifestyle switch, from hunting and gathering to agriculture - a change that brought crowded living conditions and new infections. It is likely that all these radical changes precipitated significant genetic adaptations, with selection favouring genotypes most suited to the novel conditions.

The sequence of the human genome has revealed that modern humans differ from each other by just 0.1 per cent at the nucleotide level. I share 99.9 per cent of nucleotide sequence with you and everybody else on this planet. However these small nucleotide changes and the associated linked genes contain a wealth of clues to our evolutionary history.

The human race is still very much a work in progress. By analysing the genome of three different populations of humans, researchers have detected that we are indeed continuing our evolutionary journey, and are being constantly redirected by natural selection.

The genes that show these recent changes include the ones responsible for taste, smell, digestion, bone structure, skin colour and brain function.

This might come as a surprise to many social scientists and evolutionary psychologists that hold that the shaping of the human social behaviour and mind was complete in the pre-agricultural past, 10,000 years or more ago.

Some examples of genes recently selected for are those that confer resistance to malaria in African populations or the lactose tolerance shown in adults in Northern Europeans that allows us to enjoy our yoghurt for breakfast even after we are weaned.

However, most interestingly is the finding that among the gene variants selected was some that arose from the need to detoxify plant toxins and others that mediate taste and smell. This might signal a shift in diet from wild foods, consumed raw, to a diet dominated by domesticated plants and animals that are cooked or processed in some way.