THE PALAEO DIET EXTINCTION

Researchers  led by  University of New Mexico biologist Felisa Smith report in  Science  that on all continents, large mammals started to die out  around the same time  humans first showed up.  According to Scientific American :

modern elephants, rhinos, giraffes, hippos, bison, tigers and many more large mammals will soon disappear as well, as the primary threats from humans have expanded from overhunting, poaching or other types of killing to include indirect processes such as habitat loss and fragmentation. The largest terrestrial mammal 200 years from now could well be the domestic cow …  

In the time line of mammalian extinctions, large animals started to disappear only after humans or their hominid cousins showed up. But could that be a coincidence? Others have argued the main culprit behind these die-offs was the changing climate. 

In their new study Smith and her team compiled a database of all terrestrial mammals that lived from 65 million years ago until today. They divided that time line into one-million-year chunks, and analyzed extinction trends for each of them.

 "We found absolutely no effect of climate on mammalian extinction over 65 million years"  she says.

But starting around 125,000 years ago and continuing until today, large-bodied mammals have been more likely to go extinct than smaller ones, the researchers found. The average size of surviving mammals has decreased as a result... 

In North America the average mammal weighed around 98 kilograms before the ancestors of humans showed up. Today the average size is closer to eight kilograms… 

This finding does not mean climate-related changes could not have stressed some wildlife populations, enabling humans to more easily bring about their eventual downfall