Male lions chase away young male cubs as they reach puberty and sexual maturity for several reasons:
1. To reduce competition for females. The dominant males want to ensure they can mate with the pride's females without competition from other adult males. Young males entering adulthood pose a threat to their access to females.
2. To assert dominance. Forcing subordinate males to leave the pride is a way for the alpha males to reassert their dominant status and authority over the group.
3. To limit potential challenges. By expelling younger males, the dominant males reduce the chances of a direct challenge to their leadership of the pride. Younger males are more likely to challenge older, established males.
4. Resource limitation. Prides have a limited capacity for providing enough resources for all males. Expelling younger males helps ensure that the limited resources go to the prime breeding males.
5. Inbreeding avoidance. By dispersing younger males, the pride avoids the risks of inbreeding by preventing close relatives from mating within the small pride group.
So in summary, male lions employ these tactics to maximize their reproductive success, maintain their dominance, control access to scarce resources, and promote genetic diversity. Expelling younger males serves the self-interests of the pride's alpha males.