Quirky Turning Points Of Evolution
http://abcnews.go.com/sections/scitech/DyeHard/dyehard.html
While clearly scientific speculation at this point this piece indicates how small edges can lead to major opportunities when it comes to evolution and population dynamics. Imagine how tough it was on protohumans to live with hyenas. It was tough folks we almost didn't make it as evidenced by the large number of dead amongst our hominid relatives.
Being a scrawny animal that needed brains to survive is the only path to intelligence demonstrated on this planet and it is a very risky one.
Regards,
Mark