Leroy et al., 2023

The role of meat in the human diet: evolutionary aspects and nutritional value

Hunter gatherer diets and the naturalistic fallacy

Evidence does suggest that many pre-agricultural societies derived substantial amounts of their daily calories from animal products (Cordain, 2000). However, this does not suggest that modern humans should do the same. To make this argument is to fall prey to what biologists call "The naturalistic fallacy": just because humans' 'natural' diet thousands of years ago involved meat, does not mean that eating meat is good or necessary today. Most ancestral human societies had very high rates of war and violence (Pinker, better angels of our nature), does this mean war is natural and good? Is this evidence that we should resist calls for peace, as it is inconsistent with our ancestral behaviour?

Furthermore, simply because preagricultural humans derived significant amounts of protein from animal products does not mean this was optimal for their health. As such, it is unclear whether ancestral diets can tell us anything at all about the longevity and health of modern humans. It simply means it was probably the best diet available to them at the time. By definition, pre agricultural humans did not have access to any modern fruits or vegetables, which have been transformed by modern agricultural science to be massively higher in nutrients. If our ancestors had access to modern fruits and vegetables, it is debatable whether they would have chosen to derive most of their calories from animal products.

Furthermore, there is a question of whether ancient cultures can tell us anything meaningful at all about the health of modern humans. Human life expectancy in pre-agricultural times has been estimated to be around 31, closer to a wild chimpanzee than modern humans. hunter-gatherers at age 30 likely had the same probability of death as present-day Japanese at the age of 72. Even if we make the radical assumption that their diet kept them in perfect health until their 30s when war or disease struck them down, it is an extremely large logical leap assume this diet would be optimal for someone hoping to live 70 more years. A second relevant difference is exercise amounts. While there is great cultural variability in exercise, it is typical for modern hunter gatherers to walk 8-16km per day, almost every day of the week (O’Keefe et al., 2011; Wood et al., 2021).

However, some would argue that if large amounts of meat , the meat eaten by our ancestors is different to the meat of domestic animals. Wild game meats, for example, are lower in saturated fat and provide moderate to high protein as well as higher shares of monounsaturated and polyunsaturated fatty acids when compared to meat from domesticated animals (Mann, 2000; Onyango, Izumimoto, & Kulima, 1998; Talbot, Payne, Ledger, Verdcourt, & Talbot, 1965)

The transition from a hunter gatherer diet to an agricultural one caused an explosion in the human population. A hunter gatherer lifestyle, with it's high amounts of animal products, was unable to sustain human populations above a 5 million people. We will not lapse into the naturalistic fallacy here as the authors did: this does not imply that our modern meat based diet cannot sustain large populations. Indeed, the population growth over the last 100 years disproves this. Nonetheless, there is (good? some?) evidence that current levels of animal product consumption will be unable to sustain humanity as we approach 10 billion people (probably, need citations for this, could be wrong).

An evocative counter example to the ‘our ancestors loved meat’ argument

Meat and #eggs trigger sickness and vomiting in pregnant women (known in the west as morning sickness, though it can occur any time of the day) more than any other food group (reviewed in Flaxman and Sherman, 2000; see also Holland and O’Brien, 2003). This is thought to be a natural adaptation to the fact that meat and eggs typically contain more pathogens than plant-based foods, and so historically would have provided a risk to developing foetuses (see Fessler, 2000 for a review). Ancient cultures have long realised the risks meat can pose in certain contexts such as pregnancy, as most have taboos restricting pregnant women’s meat consumption (Fessler 2000, Fessler and Navarette, 2003).