Fertility decline; no mystery

The economic opportunity hypothesis states that perceived shrinkage of opportunity discourages women or couples from embarking on marriage or reproduction. On the contrary, the sense that opportunity is expanding encourages couples to raise their family-size target. The hypothesis assumes that humans are genetically programmed to maximize successful reproduction by having more offspring when environmental/economic conditions appear favorable, but exercise restraint — waiting or limiting the total number of offspring — if the latter strategy promises greater longrun success.