There is likely a sub-set that strives to get lot of children. This could be driven by biological and/or cultural source. But there is also large set that don't

There is likely a sub-set that strives to get lot of children. This could be driven by biological and/or cultural source. But there is also large set that don't... So it there might eventually be increase in rate of child production. The length interim time is however very good question.