THE DEMOGRAPHIC TRANSITION IS ROOTED IN SOCIAL STRESSING OF MALES TRIGGERING EPIGENETICALLY INDUCED INFERTILITY OF EXOGAMOUS (FEMALE) OFFSPRING, TO COMPROMISE OUT-GROUP REPRODUCTION, FORESTALLING NATAL GROUP EXTINCTION.

A hitherto unidentified underlying basis of the globally ubiquitous demographic transition is suspected from causality-testing economic models, problems with anthropological hypotheses, and the longstanding opacity of aetiology unrelieved by integrating theory from different fields. Given a newly found main factor of population density, there is an apparent biological basis that rather than out-breeding depression is likely the now-replicated finding of chronic crowding stress of male mammals epigenetically transmitted to female offspring only, triggering multi-generational fertility decline and aberrant reproduction-related behaviours. The mechanistic core is found in humans. It's adaptive in aiding natal-group survival of neighbouring-group hostility, through exogamous natal-group females severely compromising out-group male reproduction, without impeding that of natal-group males; this complementing apparent female clique-based facultative co-operative breeding. [ABSTRACT FROM AUTHOR]