For the species or society, likely none. But consider the individual gene. Assume there's a gene X, that causes a desire to have many children. Let's say people

For the species or society, likely none. But consider the individual gene. Assume there's a gene X, that causes a desire to have many children. Let's say people with gene X have twice as many children on average as people without it. The society is affluent, so all of those children survive and spread the gene further. Eventually gene X will become dominant in the gene pool. (The fate of such a gene is quite different if food is scarce and there's a danger of starvation, which has been the case for most of human history.)