Meat has been a crucial part of our diet for millions of years. However, feeding a meat-heavy Paleo diet is far from easy. Even modern hunter-gatherers only manage to kill a big mammal once a month. It was likely even harder for earlier human species, whose most advanced equipment would have been a sharp rock.
As such, it's long been thought that humans - both ancient and modern species - relied heavily on scavenging. This raises the obvious question: how picky were they when it came to these leftovers? Modern sensibilities would suggest they avoided rotten food. I'm certainly quite picky about how much mold I'll tolerate on my lunch.
However, loathe as I am to admit it, it turns out that putrid food can be surprisingly beneficial. A review of the evidence suggests not only could it form a key part of the hominin Paleo diet; it actually did.
The benefits of rotten food
Rotten food smells gross and generally sounds like a bad idea. However, paleoanthropologists were unconvinced by the "argument from ew". So they set out to review how bad rotten food might be, and whether there is any anthropological precedent for its consumption.
Their results revealed that there can be surprising benefits to eating food that's gone a bit off. At the most obvious level, it breaks down the food. Mushy, rotten food is easier to consume and digest than it's more solid counterpart. Getting easier access to nutrients is thought to have been important for human evolution. Our ancestors may have cooked our chopped up food, but what if they just waited for nature to take its course?
In fact, the way food breaks down can actually help keep it free from pathogens in a strange way. Bacteria that feed on the lactic acid of rotting meat and fish rapidly rush in. This essentially locks out the more harmful bacteria which can't get a foothold for weeks, if not months.
As well as keeping the food somewhat safe, these bacteria gobble up all the oxygen. The resulting anerobic environment favours the preservation of vitamin C. Normally you'd have to find some fresh fruit and veg to get this crucial vitamin, or you could just let the bacteria work their magic.
Modern fondness for putrid food
"But wait" I hear you say, "most people don't like rotten food, surely that evolved". Ah my sweet summer child, that's actually a WEIRD perspective. And when you begin looking at a more normal point of view that you find a startling amount of evidence for people enjoying rotten food.
In fact, a recent review of the role rotten food may have played in the hominin diet contains three whole pages of historical references of people who enjoyed rotten food. This includes first contact reports of indigenous people enjoying rotten food, as well as more recent anthropological studies on the subject. My favourite ones are where all the judgy Europeans actually try some and enjoy it.
It's worth remembering that this can't be used to make grand inferences about human evolution either. It's also a fairly limited sample. So if you were to try and make a declaration based on this data you'd fall into the same problem as those who use too many WEIRD samples. However, it is enough to indicate that the hatred of rotten food isn't as widespread as you might think just from looking at the West.
Since it isn't as universal as it first appears, the evolutionary history of this behaviour is suspect.
Finding the Paleo diet
Of course, it's all well and good talking about how great rotten food is and how many modern groups are partial to it. But we're curious about where it fits in human evolution. Was it really part of the Paleo diet?
Figuring this out is rather challenging. We only have the bones of our ancestors' prey, which tell us precious little about the state of the meat that they ate. However, these bones do contain some indicators that they weren't the freshest cuts of meat: tooth marks.
One of the key indicators that our ancestors were scavengers is the fact they didn't get first access to meat. At many sites, particularly early ones, the cut marks (made by hominins) are on top of tooth marks (made by carnivores). Or the tooth marks are on the meatier part of the bones, whilst the cut marks might be focused elsewhere. Both of these are strong indicators our ancestors got to the meat after some carnivores (or even other scavengers) had their way with it.
This is readily apparent at Olduvai Gorge, one of the first ancient tool sites discovered. Some of the animal bones there tell a very interesting story. First, carnivores killed their prey and took bites out of the prime pieces; leaving behind telltale toothmarks. Then it was the humans' turn, using stone tools to crack open their bones and extract the marrow. Finally, another set of animals gobbled up some of the broken bone for grease.
Caveats galore
Of course, there are also early sites that show hominins getting first access to the kills. And the extent they scavenged is debated. Sometimes people will look at the same skeleton and come to different conclusions. Even when we can be more confident early humans were scavenging, we don't know the time period it took place in. Had the food gone rotten yet? Or was this all a single day of fighting carnivores for prey?
Given the paucity of data on the subject, it's likely we'll never find a definitive answer on the subject. However, it is clear that rotten food isn't quite the taboo it is in Western communities. It can, and sometimes is, a key part of the diet. It stands to reason that it was also sometimes a key part of the hominin diet; particularly given they were frequent scavengers. But to suggest it was a crucial part of human evolution is to overstate the evidence a bit.
So I think it's been a big omission from modern Paleo diet advocates. If you really want to eat like our ancestors did (at least sometimes) be sure to leave your meat on the side for a few days before you eat it. Or if you want to have a really authentic Paleo diet, have a predator maul it first.
References
Berbesque, J.C., Wood, B.M., Crittenden, A.N., Mabulla, A. and Marlowe, F.W., 2016. Eat first, share later: Hadza hunter-gatherer men consume more while foraging than in central places. Evolution and Human Behavior.
Capaldo, S.D., 1997. Experimental determinations of carcass processing by Plio-Pleistocene hominids and carnivores at FLK 22 (Zinjanthropus), Olduvai Gorge, Tanzania. Journal of Human Evolution, 33(5), pp.555-597.
Domı́nguez-Rodrigo, M., 1997. Meat-eating by early hominids at the FLK 22Zinjanthropussite, Olduvai Gorge (Tanzania): an experimental approach using cut-mark data. Journal of human Evolution, 33(6), pp.669-690.
Potts, R. and Shipman, P., 1981. Cutmarks made by stone tools on bones from Olduvai Gorge, Tanzania. Nature, 291(5816), pp.577-580.
Speth, J.D., 2017. Putrid Meat and Fish in the Eurasian Middle and Upper Paleolithic: Are We Missing a Key Part of Neanderthal and Modern Human Diet?. PaleoAnthropology, 2017, pp.44-72.
