Rob -

You mentioned that

> I once watch a nature show in which male lions would kill cubs.  The
> narrator said this was because the females would not go into heat, and
> therefore not mate, if they had cubs.  I find this odd, since aside from
> cruely, it does not seem to benefit the species.
>
> -Rob

The reason you find it odd is a common confusion about the role and extent
of altruism in the evolutionary contest of life. What you have to remember
is that male lions kill the cubs of *other males* not their own cubs.
They're not being "cruel" so much as being genetically pragmatic: they're
taking steps to insure that during their (probably short) tenure as the
pride's only breeding male, they maximize the chance of long-term
reproductive success. The motivations in killing the cubs are, a) to free up
the females for mating anew, b) to reduce the resources of the pride that
are diverted toward other male's offspring, and c) to eliminate potential
future competitors for pride dominance.

(Note: nothing I say about evolution should be construed to imply that I'm
giving any behavior any kind of moral approval or disapproval. When I
discuss evolution, it's in the spirit of trying to learn how things work,
not to cast moral judgements.)

Ken Green