At several key points in pre-history we came close to missing our evolutionary curtain call. Leakey identifies two ways in which species disappear. The first are ordinary or 'background' extinctions where those that fail to adapt are slowly replaced by more adaptable lifeforms. In the second, large numbers of species go to the wall in relatively short periods of biological time. There have been five of these, each provoked by cataclysmic evolutionary events caused by some geological eruption, climate shift or space junk slamming the earth.
Survival becomes very arbitrary.
Pause for thought really. But Leakey has another purpose in writing The Sixth Extinction . The degree of chance involved in human evolution should be cause for modesty and a semblance of respect for our fellow lifeforms. It has not been. The figures showing the rapid rate at which we are destroying the biodiversity around us are staggering.