In the Scientific American November issue cover story paleontologist Lars Werdelin of the Swedish Natural History Museum in Stockholm observes that the large-bodied carnivores inhabiting East Africa today represent a small fraction of the diversity this group once had. He argues that competition with humans for access to prey drove many of these species to extinction, starting more than two million years ago. It’s a bold hypothesis. Although researchers know that early humans began incorporating more meat into their diet around that time, the conventional wisdom is that ancestral population sizes were small. Could our few, comparatively wimpy ancestors really have beat the saber-toothed cats and other formidable carnivores at their own game? Werdelin makes a compelling case.

Readers might wonder whether climate change better explains the decline of these beasts. Shifting climate drove many faunal changes over the past few million years, but it does not seem to be the culprit in this case of disappearing large carnivores. For one thing, if climate change were the cause, one would expect small carnivores to decline, too. Yet studies indicate that they experienced no such downturn. As the chart below shows, unlike their large counterparts, small carnivores did not lose any functional richness (dietary diversity) in that time. In fact, the data hint that this group’s functional richness may have even increased, although that apparent uptick may just be an artifact of the better preservation of younger fossils compared with older ones.