Final answer:
The primary benefit of infanticide by a new dominant male lion is to ensure that his genes are passed to future generations by making female lions ready to breed again sooner. It is a behavior driven by the imperative of gene propagation. Additional benefits include resource saving and reinforcing dominance but are secondary to the reproductive advantage.
Step-by-step explanation:
Infanticide by a new dominant male lion confers the primary benefit of ensuring that the dominant male's genes are passed on to the next generation. This behavior occurs because female lions are ready to breed again sooner when they are not caring for cubs. This means that once the new dominant male has taken over a pride and commits infanticide, the females quickly become receptive to mating, thus the male's own genes will be propagated when the new cubs are born. It is also important to note that not spending resources on cubs that aren't his and not having to care for unrelated cubs can be secondary benefits, and the aggressiveness of the act may reinforce the male's dominance, but the primary evolutionary benefit is the increase in reproductive opportunities.
When male lions reach sexual maturity and are ousted from their pride, they can affect genetic diversity and allele frequencies of the population through natural selection and genetic drift. The success of taking over a new pride and producing offspring would depend on certain traits, potentially shifting allele frequencies over time.