Many animal populations have non-reproductive members. It takes a village to raise a child. In such an extremely social animal as Homo Sapiens, many of our adaptations are social. E.g. it only takes a few men to guarantee another generation, yet 50% men are born in each. Another: we don't die the instant we give birth; we're there (and non-reproductive) for decades afterward, competing for resources. Its the social benefits that allow for this.