Biological Consequences of Declining Human Fertility.

Human fertility has been declining for over a century, especially in economically developed nations. This decline is a result of the changing socio-economic situation that triggered the "demographic transition." The progress in medical sciences and in living conditions has resulted in a strong reduction of infant and child mortality, which, together with increasing family economic expectations and female economic independence, has produced a situation of a few children being born. It appears that the short time over which the fertility declined and the socioeconomic causes of this decline did not allow directional forces of evolution to affect biological determinants of human reproductive abilities. It is argued here that the alteration of the mutation/selection balance over the lifetime of a few generations is sufficient to affect human ability to produce offspring-fecundity-and thus we have already entered R.Aitken's "post-transition trap" that reduces "future fecundity of our species." It is no longer just a hypothesis. Reduced fertility will lead to a situation in which the use of artificial reproductive technologies will become an increasingly more relied upon way to reproduce humans unless methods to remove from the gene pool deleterious mutations affecting human fecundity are developed.