Mother Nature... the bloody bitch!
I think the various accounts of infanticide amongst primates kind of indicates that the evolutionary process is as nasty as it is creative, by human standards. But it's also what creates our good sides - altruism and other helping behaviours have deep evolutionary origins too.
All a bit like Vonnegut's "God the Utterly Indifferent" or in New Testament terms "God sends rain on the good and evil alike".