Thesis #46 – In the last ten to twenty thousand years, some human populations adopted extensive agricultural cultivation of grass species and the use of milk from other mammals for nutrition, a novel environment which changed the action of natural selection among populations in Eurasia and elsewhere.
But the majority of humans now living come from ancestries in which agriculture has been the normal source of food for some hundreds of generations. Furthermore, associated with this dietary transition has been a change of lifestyle to one which features much less roaming about the landscape. Instead of frequent travel across a wild landscape, settled human civilization has featured relatively sedentary occupation and use of small plots of land, chiefly organized around villages that involve fixed habitation.
From an evolutionary biologist’s perspective, evolution took a hunter-gatherer species and initiated a large-scale experimental evolution project, in which most of our species was selected to adapt to a novel regime of diet and activity. Instead of diverse foods, including a fair amount of animal body parts, agricultural populations have been eating diets in which the seeds of grasses and, in some cases, the milk of other mammals have been our nutritional staples. This is one of the most abrupt shifts in nutrition undergone by any species known to us in the history of biological evolution.
This is not, however, the first such shift in hominin evolution. Around three to five million years ago, current evidence suggests that we began to dig up, clean, and cook the underground storage organs of plants, such as tubers and roots. At this point in our evolutionary history, we began to evolve amylase genes that have since helped us to digest starchy plant foods, foods with many of the dietary properties of the potato or the yam. It is likely that our early tool use and moderate brain size allowed us to learn and culturally transmit the cultural practices required to sustain this early “cooking” niche.
As our tool use and our social cooperation became more proficient, around a million years ago we added frequent hunting to our ecology, which led to another change in our diet and activity levels. This was when our brain sizes started to expand rapidly, thanks to genetic evolution. It is also when we are thought to have acquired an improved capacity to digest and transport fats within our bodies, particularly compared to other ape species, which eat prey much less often.
But notice the time-scales of these transitions. We spent several million years adapting to a diet that featured digging, gathering, and cooking roots and tubers. We then spent about a million years adding hunting to our underlying gathering/cooking way of life, and evolving accordingly. By contrast, even the agricultural populations of greatest age have been using grass seeds as their predominant nutrient only for tens of thousands of years. This set the stage for a remarkable evolutionary transition, but one that is still “in process,” rather than a settled achievement of evolution. This is the key point for a possible revolution in human health, a revolution to which we now turn in the 55.