150,000 years the human race was almost wiped out due to massive droughts in Africa. Estimates were that fewer than 2000 modern humans remained @ that time and every one on the planet can trace their roots back to an single individual 200,000 years ago. In 150,000 years the earths current races came from a single source "a cosmic blink of the eye".
I propose the following scenario:
7 Million years ago on the plains of Africa a small group of Hominids looked nervously @ the sky. It was literally rippling with auroras caused by an Supernova that exploded 125,000 light years away. The resulting Gamma burst was a near miss in cosmic terms but powerful enough to strip off 10-17% of the Ozone layer.
Eco systems crashed and the opportunistic hominids were left to fill the gaps of 75% of existing life forms. Humans still evolve but in a very different world where Humanities earliest ancestors have filled the Gaps from predator to prey.
Thoughts.