Which behavior reduces the reproductive fitness of the original male in a social group?

Infanticide is a behavior where an adult animal, typically a male, kills the offspring of another. This action can reduce the reproductive fitness of the original male because it directly impacts his chances of reproducing successfully. By eliminating the young, especially if they are offspring of rivals, the infanticidal male may increase his own chances of mating with the female sooner, as she may become receptive to mating again after losing her young.

However, this behavior is detrimental to the original male's fitness because it can lead to increased aggression from others in the group, potential retaliation, and loss of social alliances. Additionally, if the original male’s offspring are targeted, it results in the loss of his genetic contribution to the next generation, thus decreasing his reproductive success.

In contrast, altruistic food sharing, grooming, and dominance behavior generally serve to enhance social bonds, increase survival, or improve the male's standing within the group, thus typically contributing positively to reproductive fitness.