EmpiricalRequires evidence

Small changes in individuals produced an enormous change in the species, and the effect was invisible at the level where it happened. Part I: the true effect of these cognitive changes was not visible individually, and slightly more creative and flexible individuals aggregated to produce an enormous shift in our capabilities as a group. The measure of that shift is the extinction record. Within a few thousand years of reaching Australia, twenty-three of the twenty-four Australian animal species over 100 pounds were gone; within two thousand years of reaching the Americas, North America lost thirty-four of forty-seven genera of large mammals and South America fifty of sixty. Part I makes the right point about it: ecological devastation is common in the record and almost always external, usually climate, and the spread of Homo sapiens was the first time a single species precipitated a change of that magnitude.

Risk landscape