What diet did humans evolve to eat?
grains, seafood, beef, milk, samosas, alcohol
Human evolution hasn’t stopped. We continued to evolve through the agricultural revolution—which started around 15,000 years ago—and we continue to evolve today. In fact, human evolution may be happening more quickly than ever before, and genes related to immune system and food metabolism are among the most strongly selected in the recent past.
To find recent selective pressures, researchers sequence the genomes of many people and look for statistical patterns. For example, a genetic variant that underwent recent positive selection may be as common as an older variant but will have less variation around it. (because as a variant is passed down from one generation to the next, it’s neighboring variants are passed along with it, and more recent variants will have less time to have accumulated variation around it than older variants.)
As humans spread across the world, they relied on different food sources. Some settled in the plant rich jungles, others in fertile valleys, or arid deserts, and a few in the frigid lands of the arctic. Other new food pressures were shared, such as developments in agriculture.
The genetic variant conferring lactose tolerance in Europeans emerged about 20,000 years ago, and is now present in over half of the population of the UK. But lactose tolerance didn’t just emerge once in a single population. It emerged multiple times, each time as a different genetic variant. A few times in sub-Saharan Africa and twice in Arabia. I think it also likely emerged in the Buryat population of southern Siberia where my mom was born and raised (they drink a lot of milk)—though a study would have to be done to test for this.
The most prominent lactose tolerance variant in sub-Saharan Africa is the same age as the European variant, about 20,000 years old. (The age of a variant is similarly based on statistical methods that look at how similar the regions around a variant are.) For both variants to be around 20,000 years, means they both probably arose due to the same new dietary challenge of digesting dairy. For comparison, many variants are hundreds of thousands or millions of years old. Lactose tolerance is a striking example of convergent evolution, where different populations developed a similar solution to the same challenge.
Our ancestors, in some cases, also adapted to different food pressures. The Inuits of Greenland traditionally ate a diet heavy on seafoods and mammals like seals. Indians, on the other hand, are famous for having regions with traditional vegetarian diets. The Inuit and Indian populations have experienced opposite pressures when it comes to a group of genes that metabolize fat. There’s an ancestral and derived variant linked to fat metabolism on a cluster of genes called FADS. (Since one is ancestral variant and the other is the derived, you can only have one or the other). In the Greenlandic Inuit the derived variant is under positive pressure, but in Indian populations the ancestral variant is under positive selection pressure. The ancestral variant is also under positive selection in East Asian populations, but to a lesser degree. I’m not sure exactly what this variant does to fat metabolism, but I think it has something to do with Omega-6 fatty acids—the biochemistry gets complicated for me. But to me, it is amazing to see that small differences in our metabolism can be evolutionary meaningful.
There are other adaptations that have been discovered. In East Asians, selection pressures have acted on alcohol metabolism. People with the derived variant metabolize alcohol up to 100x faster (I wish I had this variant) and protects against alcoholism. It also associates with the characteristic flushing seen in some Asians. The authors of a recent paper linked it to the emergence of rice agriculture and fermentation of alcohol in the region. Other societies that were also heavy alcohol drinkers likely evolved different adaptations.
Metabolism is a polygenic trait, meaning that many genes contribute to it. If we look at the metabolism overall, it needs to process proteins, fats, carbohydrates, and all of the micronutrients that our bodies need, and this requires the coordination of many different genes. Genes can be turned on, off, or amplified. As in the case of lactose tolerance, the enzyme, lactase, simply needed to not be turned off once a child is weaned. Another enzyme, amylase, which helps digest starch is carried in greater numbers in populations that have more starch in their diets.
On top of these population level differences, we all carry rare genetic variants that may change how we metabolize or react to certain foods on a personal level. Some of these variants may be completely unique to us and no else in the world may share them. Others we share with our close relatives. These can cause more serious metabolic conditions or simply result in having sensitivities or reactions to different foods.
Looking at our ancestors’ diets doesn’t replace contemporary nutritional science research, but it informs nutritional science researchers that including diverse and underrepresented populations is important.
I personally think that our ancestors’ diets held a lot of wisdom. Our ancestors weren’t just adapting to their diet, but they were actively choosing their diet based on what tasted good, what made them feel good, and what made their kids grow big and strong. How old is the saying, “An apple a day keeps the doctor away”? It’s still good advice. Even more relevant advice may come from listening to the experiences of our close relatives who share a lot of our DNA.
A lot of people have strong feelings about this diet or that diet, and maybe those strong feelings stem from the fact people’s metabolisms respond differently to different foods. But there is one thing that is universally agreed upon: ultra-processed foods are bad for us. Evolutionarily this makes sense.