Here's an interesting article in ScienceMode about how humans are still evolving, more rapidly than ever, and with increasing differences tied to the separateness of continents.
Think about it, particularly in light of recent reports that seem to add confidence to the theory that modern humans are the result of migration "Out of Aftrica" 50,000 years ago (replacing Neanderthal in Europe and Homo Erectus in Asia), rather than Multiregional evolution resulting from Homo Erectus migration from Africa 1-2 million years ago with evolution into Homo Sapiens occurring independently (more here).
Back to the original article cited, with some excerpts.
The study looked for genetic evidence of natural selection – the evolution of favorable gene mutations – during the past 80,000 years by analyzing DNA from 270 individuals in the International HapMap Project, an effort to identify variations in human genes that cause disease and can serve as targets for new medicines.
The new study looked specifically at genetic variations called “single nucleotide polymorphisms,” or SNPs (pronounced “snips”) which are single-point mutations in chromosomes that are spreading through a significant proportion of the population. […]
Over time, chromosomes randomly break and recombine to create new versions or variants of the chromosome. “If a favorable mutation appears, then the number of copies of that chromosome will increase rapidly” in the population because people with the mutation are more likely to survive and reproduce, Harpending says.
“And if it increases rapidly, it becomes common in the population in a short time,” he adds.
The researchers took advantage of that to determine if genes on chromosomes had evolved recently. Humans have 23 pairs of chromosomes, with each parent providing one copy of each of the 23. If the same chromosome from numerous people has a segment with an identical pattern of SNPs, that indicates that segment of the chromosome has not broken up and recombined recently.
That means a gene on that segment of chromosome must have evolved recently and fast; if it had evolved long ago, the chromosome would have broken and recombined.
Harpending and colleagues used a computer to scan the data for chromosome segments that had identical SNP patterns and thus had not broken and recombined, meaning they evolved recently. They also calculated how recently the genes evolved.
A key finding: 7 percent of human genes are undergoing rapid, recent evolution.
Essentially, what it boils down to is that with massively increased population comes a huge increase in the speed of evolution, which makes intuitive sense. If you observe genetic mutations of bacteria in some culture, the rate of mutation and hence the rate of beneficial mutation that gets passed on, resulting in evolution of the bacteria, is going to be directly proportional to the size of the colony — the more bacteria, the more chances for mutation, natural selection, evolution; repeat.
The implications for diet are clear. What is the single most important change in human civilization leading to massively increasing population growth? Agriculture. So, on the one hand, we are evolving to perhaps eventually handle grains and other processed food oddities. However, we're certainly not there yet and it will probably take some thousands — though probably not tens of thousands — of years to fully adapt. For example, most of European decent have already adapted to handle milk & dairy while most of Asian ancestry have not (they don't produce lactase).
But Harpending believes the speedup in human evolution “is a temporary state of affairs because of our new environments since the dispersal of modern humans 40,000 years ago and especially since the invention of agriculture 12,000 years ago. That changed our diet and changed our social systems. If you suddenly take hunter-gatherers and give them a diet of corn, they frequently get diabetes. We’re still adapting to that. Several new genes we see spreading through the population are involved with helping us prosper with high-carbohydrate diet.”
Of course, this raises the question of whether you want to be part of the evolution going forward, i.e. "do your part for the human race," or do you want to live in accordance with the genetic makeup you already have, which implies a Paleo-like diet of meat, natural fats, vegetables, fruits and nuts to the exclusion of grains, refined vegetable oils, and processed foods?
I know what path I'm taking.
(HT: Art's private blog)