A little more than one million years ago the Mesopotamian dawn mammals, the direct descendants of the North American lemur type of placental mammal, suddenly appeared.  They developed an extraordinary fear which led to those wise precautionary measures that so enormously contributed to survival.  They gave rise to mid-mammals after 70 generations. 
When the numbers of this new and superior group grew great, war, relentless war, broke out; and when the terrible struggle was over, not a single individual of the pre-existent and ancestral race of dawn mammals remained alive. 
The immediate lemurlike mother of the dawn-mammal species escaped death no less than five times by mere hairbreadth margins before she gave birth to the father of the new and higher mammalian order. 
These small animals walked mostly on their hind legs, and they possessed large brains in proportion to their size and in comparison with the brains of other animals.  They experienced many of the emotions and shared numerous instincts which later characterized primitive man.  They were, indeed, highly gregarious but nevertheless exceedingly pugnacious when in any way disturbed. 
See also: UB 62:2.