As natural is a word with a vast definition, diet is one with almost unlimited scope. Hence, the exploration of a natural diet as the touchstone of optimal health is but a Grail quest.

The omnivorous Diet of the San and Hadza interest us because modern hunter-gatherers are largely spared the common degenerative diseases afflicting West and East. They gather wild berries and nuts, hunt insects and small game, not the kind of fare that interests most of us, though nutritious. But do they represent a nutrition that molded our biology and genetics that we ought to imitate today?

Let’s look back in prehistory to when humans were evolving from apes, before they lived in degraded environments. We have lost an immensely rich megafauna that offered humans meaty meals. In a recent review, Tel Aviv researchers conclude that through most of the Stone Age we were apex predators and hypercarnivores (meaning >70% meat).

That we are flesh-eaters by nature (sic) can sound scandalous, implying we are not only responsible for the ongoing Sixth Extinction but a previous one in the Paleolithic era as well. Homo species probably carried as much responsibility for destroying biodiversity as climate change (perhaps more), causing mammoths, aurochs, saber-toothed tigers, cave bears, and other charismatic animals to vanish. I feel even more persuaded after my single experience of practical paleontology cleaning bones of a local Mastodon: our geologist, Jerre Johnson, declared it was killed by hunters.

The first hominids were primary vegetarians, like their ape antecedents. Before we emerged as a distinct species, our lineage was represented for a couple of million years by Homo erectus. By the Upper Paleolithic, a few tens of thousands of years ago, they helped to make large game scarce. We had to switch to a mixed diet of hunting and gathering, fishing and domesticating animals for meat and milk. The hunger for greater food security triggered the first Agricultural Revolution, and crop farming was so successful it created a population boom with social changes we still grapple with.

So, what is the evidence for carnivory? The authors reviewed 25 factors, including genetics and physiology, ecology and paleontology. Here are a few memorable examples, not just from gut and metabolism.

• A highly acidic stomach adapted for killing bacteria in stale meat and carrion is absent in obligate plant eaters.
• An adaptation for high fat consumption and insulin resistance
• Micronutrients from animal sources (vitamin B-12 a top example)
• Higher ratio of the length of small intestine to colon
• Changes in masticatory apparatus and salivary enzyme genes for starch digestion
• Endurance running and excess sweating for catching swift prey
• Ability to throw weapons forcefully and accurately (chimps and gorillas can’t throw 100 mph fastballs)

Charles Darwin believed changes in diet shape evolution, famously illustrated by Galapagos finches. Maybe it’s hard for vegetarians and vegans to accept we are still adapted for a low-carb paleo diet, but our evolution creeps slowly because of long generation intervals. Eating mostly plants is no longer just a personal preference or from concern about animal welfare, but a virtue for lowering our impact on the environment. We never worried before about going against the grain by denying our nature of two feet on the ground when we wanted to launch into flight and space. Neither should we now.