If you are shocked at how the harem of a lion behave when he gets a challenger, you don't get eugenics. It actually makes sense that the lionesses behave like that ie not help the lion, allow him to be defeated which will mean their cubs will be killed by the victor. That is because they understand eugenics, while we do not.
The lionesses know that the future of their species is more important than their affection for the offspring and the father of their offspring. They must always bear the offspring of the strongest available male, for the sake of their species.