What did humans evolve to eat?
The human brain is the obvious smoking gun that answers the question: what did humans evolve to eat?
The vast size and energy demands of the human brain required a diet that differed from that of our hominid ancestors.
Are we herbivore vegans or carnivore wolves?
Without fail the information that supports the argument is cherry-picked and that which doesn’t is omitted. There are almost always half right and half wrong. Because what is almost always omitted in both cases is the big picture.
Our Evolutionary Ancestors
Humans, the genus Homo, evolved from early hominids that lived in the trees, ate fibrous plants, and were undoubtedly herbivores. Our heritage is from the great apes, and our digestive tract would not have allowed a meat-heavy diet. We had large cecums that turned fiber into fat. This was our main source of energy. Too much meat would have twisted the colon and been extremely painful and even life-threatening.
Climate and environmental changes about 3 million years ago brought us to a crossroad. As rains became more scarce so did high-quality plants. Forests became wooded grasslands, and more grazing animals populated savannas. We had to diversify our diet – with meat – or compete for a dwindling limited resource – plants.
The asutralopiths, our hominid ancestors chose to stick with plants and became extinct.
Humans chose to venture out, take a risk, and incorporated meat into the diet.
When we left the trees for the grasslands, we were untrained and ill-equipped hunters. We were also easy prey of fierce, well-trained predators. So we did the obvious, we scavenged. In the early goings, we were likely carrion feeders which means we ate on dead and rotting flesh. We’d let the professionals do the killing and we’d hurry in for the scraps and return to safety.
Although we weren’t great killers in the early get-go our stomachs evolved through natural selection to do pathogen fighting for us. Our stomachs became very acidic. The acid in our stomachs killed off pathogens that resided in the rotting animals we scavenged and it also enabled improved digestion of meat.
Acidic stomachs separate carrion feeders and carnivores from herbivores. The acid filters out the bad pathogens while facilitating digestion into the small intestines. Baboons for example, who are considered one of our closest relatives, have stomachs that are about 1000X less acidic than ours.
From Supplement to Staple
Meat started off as a supplement to our plant-based diet. As the weather and environment continued to change, so did our diet, and so did our evolutionary adaptations.
Meat fueled our unprecedented brain growth and cranial capacity. With this energy dense food, our guts shrank and brains grew. Eventually we could no longer meet our energy demands without meat. We became obligate meat-eaters.
Energy dense animal products were the only way we could survive, the only way we could meet our energy requirements, the only way we could feed our brains and bodies.
While we could still eat plants, they simply couldn’t fuel us themselves. We’d lost much of our fermentation ability (that could turn fiber into fat energy) that a big cecum allows for. We traded it for the ability to eat increasing larger amounts of animal meat to power an increasingly growing brain.
The evolutionary decision was choosing between a big brain (meat) or a big gut (plants).
As we became dependent on animals for food, natural selection further changed our bodies. As once poor hunters that were newly out of the trees and barely bipedal, we transformed into predator apes. We morphed into skilled hunters. Specifically, persistence hunters.
Because we chose meat and brains, evolutionary forces pushed for survival of the fittest hunters. Humans became, and are now, the only living primate adapted for endurance running. We developed a vestibular system and nuchal ligament for balanced running. Natural selection favored running enhancements like longer lower limbs with muscles like the glutes and tendons like the achilles.
Since we were no longer climbing trees the muscles in our shoulders decoupled, and we became rock throwers, then spear throwers, then baseball throwers.
Our feet evolved to absorb shock and the big toe came into alignment with the other toes as running became more important than grasping limbs. We evolved sparse and short body hair and millions of eccrine sweat glands to prevent hyperthermia.
Running from Herbivore to Carnivore
Our diet and anatomy changed step for step.
We started to share more features and habits with carnivores than our herbivore ancestors.
Unlike herbivores that graze and grind all day, we became intermittent eaters like carnivores.
Prey. Eat. Rest and Digest. Repeat.
Our gut mirrored a carnivore gut. Our cecum shrank to the point of being a useless vestigial appendage since we were no longer using it to digest plant materials like our herbivore ancestors did. Rather, our small intestines absorbed fat and protein extremely efficiently and we now share similar well-developed gallbladders to that of wolves and lions.
Since we stopped grazing and grinding all day, our facial anatomy changed as well. Our jaws main use became vertical up-and-down chewing rather than the side-to-side, rotary mechanism of herbivores.
In fact our digestive system evolved so much we became a definitive host for tapeworms. No, this isn’t the greatest of human adaptations, but we are the only other mammal besides obligate carnivores like lions and hyenas that can be a definite hosts for tapeworms.
I often see vegan arguments about our teeth. They look like herbivore teeth so we must be plant-based eaters.
Well, we are primates and our basic body is derived from this heritage. Therefore we have teeth similar to other apes in terms of size, shape and number. Yet we still have ridged molars like wolves instead of flat ones like sheep. We also have small canine teeth and relatively smaller jaws.
Humans started using tools millions of years ago and fire hundreds of thousands of years ago to kill, cut, and cook the meat. Less mastication forces were needed. Additionally, since canines were predominately defense and intimidation mechanisms, the smaller canine represents a shift in social structure and mating behavior that results from cooperation, communication, and a reduction in male-to-male conflict.
For similar reasons, we have nails instead of claws – because we are primates. Primates don’t have claws. In no way does this suggest we are designed for a plant-based diet. It suggest we are primates – which we are.
What about carbs?
As humans we can extract and use carbohydrates in plants – not cellulose though – and not efficiently. This is where humans differ from pure carnivores.
To me it’s clear we CAN eat plants and that we didn’t completely lose this ability from our evolutionary history. It is also clear that we have become ill-equipped to eat plants, some more so than others. Fiber is excellent evidence of how we’ve diverged from our herbivore ancestors as well as how poorly we use exogenous antioxidants. So just because we can eat plants doesn’t necessarily mean we should. We can drink alcohol and extract energy from it, but it’s also a neurotoxin.
Limiting things in which we have limited ability to tolerate is a smart idea.
What did humans evolve to eat?
Throughout human evolution we became more and more equipped to eat meat and less and less equipped to eat plants.
We evolved from a pure plant-eating heritage, and gradually evolved to supplement that plant-based diet with meat, which eventually led to complete dependence on meat for survival. Plants became the opportunistic supplement to a meat-based diet.
All was well in evolution until about 10,000 years ago.
At this time we shifted from a meat-based diet to a dramatic return to a plant-based diet with the Agricultural Revolution. Even worse, we started eating plants that we’d never eaten in history. The decline in nutrition sped up further with the industrial revolution, as we started modifying and refining plants as well as spraying, storing, and shipping our new food. Today most of our food is synthetic in some way.
We took food we’d become ill-equipped to handle through millions of years of evolution and made it our main dish. And we took meat which literally made us human and that we had evolved to depend on and labeled it dangerous and a health, cancer and heart disease risk.
Really our shrinking brains and modern diseases are less of a mystery and less complex then we try to make it.
If you’d like to learn more about what we are designed to eat, and how to optimize diet for health and fitness, I’d highly recommend watching the Meat Health Masterclass: