4/17/23

Megafauna Whodunnit

Megafauna Whodunnit

Who killed off all the big mammals?

Imagine we had come into the world as humans tens of thousands of years ago, mainly hairless due to the tropical climate, and we found ourselves living as hunter gatherers in a nomadic clan following big-game animal herds across vast distances. Unlike the other animals, we were capable of imagining the past and future, for thinking several moves ahead of our quarry. Beyond the hunt, we performed tasks involving our own clan’s survival: learning to share tasks involving food preparation and raising our offspring.

Viewed from our world, this past gets harder to see the farther back we look. There are too many gaps to fill. Artifacts are so rare that estimates of when our ancestors’ relatives reached the Americas varies by tens of thousands of years—longer than all of recorded human history. DNA analysis furnishes more evidence about how long ago we came into being, but the amount of time involved is speculative. The best guess today is that we go back around a quarter of a million years—the blink of an eye in Earth’s history.

Among the things we would like to know about our earliest ancestors is what we were evolved to do. We assume that most of our past was as hunter-gatherers who were probably carnivores. Evidence for this includes our shortened digestive tract, typical for scavengers. It is also possible that a significant portion of our diet was taken from other predators, since we’ve got one of the most potent levels of stomach acid in the animal kingdom, exceeded by carrion-eating vultures.

Our closest wild relatives—chimpanzees and bonobos—are herbivorous. Eating plants requires a long digestive tract in order to neutralize all the toxins plants use to defend themselves from being eaten. Nor is vegetation especially dense in accessible nutrients, so eating and digestion occupy a lot of herbivores’ time.

As Homo sapiens sapiens, we don’t have this problem; our problem was always finding game. Not only that, we appear to have evolved requirements for fatty meats, preferably cooked or predigested by means such as salting, drying, or fermentation. This suggests that we were evolved from predecessors who hunted in social groups and had mastered the use of fire.

Our ancestors spread across the world from Africa some 150,000 years ago, plus or minus tens of thousands of years—our knowledge is not that exact. Everywhere they went, large mammals disappeared. Cause and effect appear straightforward, but many indigenous groups in Australia and the Americas object to the insinuation that their ancestors caused extinctions. The conventional presentation, thus, avoids adding the insult of such an accusation to the injury of having displaced and marginalized these peoples in recent centuries.

Nevertheless, quite a few researchers have pointed out this correlation and argued that it tells us a lot about the diet we are evolved to eat as a species. Here, retired physician and Protein Power (1996) author Michael Eades summarizes the case for this reading of the evidence:

The summary is quite compressed, given that it covers the entirety of human history and prehistory in just under an hour. It omits a lot from the archeological record, but still makes for a strong case.

The answer to the whodunnit question, then, is that we very probably did.