✒ Data shows steep decline in the average mass of mammals over time. The evidence points toward one main culprit: humans.

Human have always hunted the largest mammals, which makes sense as it gives a good return on investment. One successful kill could feed a family for a long time. Bigger mammals are also easier to spot and track down.

This overhunting of large mammals might have been the catalyst for our ancestors to engineer fine and intricate tools. Once we had run out of big animals to eat, we had to engineer tools to catch the smaller ones.