That's natural selection, baby.
Not at all, because then the majority of species on our pla-
net would do it, but the opposite is the case - apart from
some egg laying insects and reptiles with an extremely high
number of descendants we are the only ones who kill mem-
bers of our own species.
Do you imagine that competitive pressures and the principles of survival of the fittest have somehow not been applicable to humans throughout our evolutionary history?
I imagine that killing members of the own species is the most
counterproductive reaction to competitive pressures and that
the "fittest" of a species are those with the best flexibility in
the adaptation to changing environments and the widest he-
reditary immunity to diseases, not those with the highest de-
veloped ability to kill others.
Besides, competitive pressures and survival of the fittest are
facts of life for all species, not only for humans. We are only
almost unique in our ways to deal with those problems, and I
tend to think that our approach is more likely to increase our
risk of extinction through self destruction than to support our