Basically, prolactin is released during/after orgasm, and this triggers neuronal stem cells to replicate. Primarily affects olfactory nerves (sense of smell) but may also help stroke, alzheimers, and other.
So, if you try to procreate, your brain repairs some of the lost neurons, which means you might be sharper, which means you might survive/be alert to dangers like leopards, so you might live longer, to procreate, loop.
This also makes me think, old grannies who are losing their memories should have sex, or at least see about prolactin as part of hormone replacement therapy.
But then, applying that to my own family grosses me out.