ernest_t_bass wrote: Mothers killing there young b/c they only had ONE and wanted a litter is neither "defense or survival."

Sure it is. Darwin would say the chance of survival doesn't justify the risks and strain put on the mother. Darwin would say the preference for the litter is efficient use of resources to ensure the greatest probability of the line being continued. Theory of natural selection that the instinct would be to "start over" with a larger litter. Those coming from lines that didn't would, inevitably, fail to continue the line and die off.

I vote for Machiavellian.

FatHobbit wrote: If you skip past the abortion stuff, there is a bit of info about animals that kill their own kind. http://en.allexperts.com/q/Wild-Animals-705/Animals-kill-young.htm

I'm aware of infanticide in the animal kingdom. I'm not aware of it not being motivated by hunger, insticts to continue one's own line, or instinct to remain the matriarch or dominant male (and thus continue the line). Again, "killing" in the animal kingdom is distinctly different from cold blooded murder; all explained by the instinct to survive and procreate. Cold blooded murder is, in fact, not natural.

The parallel with humans would be killing a rival suitor of a girl you like or killing male children of other guys so your own male children will have a better chance of multiple mates.