The figure above is kind of hard to parse, but it’s from Body size downgrading of mammals over the late Quaternary, and it illustrates that in some periods larger animals tended to go extinct, while others there was no bias due to size (in fact, large animals tended to do quite well because of their wide ranges). I was pointed to this paper by an Ed Yong piece in The Atlantic, In a Few Centuries, Cows Could Be the Largest Land Animals Left.

One of my peeves with the overall field of natural history is that sometimes researchers just want to argue about the obvious because they can. Natural history is obviously historical, and so you can’t just run an experiment and settle things. It seems pretty clear to me looking at the pattern across the past two million years across six continents that humans are not the sufficient cause of megafaunal mass extinction but they are a necessary cause.

If it wasn’t for humans, mammoths would still be around. How do I know this? They were around for hundreds of thousands of years a minimum and made it through the Emian interglacial from 130,000 to 115,000 years ago when the world was actually warmer than it is today.

The major work of the paper above was assembling a large data set across a wide time period and geographic expanses. You can see that the emergence of Homo, and not just modern humans, is really what matters. The labels above are:  LQ, average of all late Quaternary (LP to H) extinctions; LP, late Pleistocene; EP, end Pleistocene; TP, terminal Pleistocene; H, Holocene; and F, future extinctions. The end of the Pleistocene was probably bad because the shock of the climate change probably knocked out a lot of species which were already under pressure from humans.

I’ll leave you a quote from Yong’s piece:

When hominins like Neanderthals, Denisovans, and modern humans spread through Europe and Asia, the average mass of mammals there halved. When Homo sapiens later entered Australia, the mammals there became 10 times smaller on average. And when they finally entered the Americas, with effective long-range weapons in hand, they downsized the mammals there to an even steeper degree. By around 15,000 years ago, the average mass of North America’s mammals had fallen from 216 pounds to just 17.

Addendum: The reason that Holocene extinctions have a smaller size average is that there weren’t as many big mammals to kill. We’re pretty much moving down the trophic layers now….