> we suggest that infanticide is a sexually selected behaviour in killer whales that could provide subsequent mating opportunities for the infanticidal male and thereby provide inclusive fitness benefits for his mother.
I can see gene fitness benefit but mating opportunities, how?
"hey, me and maman uh killed your baby, wanna pump out a replacement real quick?"
In species where a prominent male has a harem of multiple females. This usually involves killing not only rival males, but all of their offspring too. Here's a Wikipedia article about it: https://en.wikipedia.org/wiki/Infanticide_(zoology)
In species which keep territories, animals will kill rivals of the same species, but because it's not targeted it's not genocidal, unless the species eusocial, in which case it can result in massive genocidal wars, e.g. https://en.wikipedia.org/w/index.php?title=War_in_ants
I think the distinction is between killing a line and killing a tribe. But granted, that’s valid.