The Biological Environment has a strict Birth Control Policy for all species. Control by instincts. In our case, it doesn’t restrict a male at the top of the pecking order in any culture he exists in to any number at all. For practical, political and social reasons of his own the male concerned will ensure that these cultures will be kept out of the media of the modern nation-state.
Otherwise, males in lesser cultures in any of our advanced countries today can also be restricted by the Additional Environment — the nature and earnings of his job. For this reason, populations in the advanced countries are now taking a nose-dive. Males at the top of their profession may have, let us say, six or even a dozen children. Those at the bottom — and indeed a growing number of those in the middling portion of the pecking order — are now choosing to have no children.
When economic good times resume, the Additional Environment will peel away and the very strong maternal instinct of the female will emerge at full strength.