Overall the demographic transition is characterized by
two main trends. The first trend is a reduction of fertility to
replacement or below-replacement levels (~2.1). The second
trend is a reduction of mortality that allows most individuals
in society to reach an advanced post-reproductive age (~80).
Both trends are universally associated with socioeconomic
development (i.e. "modernization") and a transition from a
pre-industrial to an industrialized economy [33]. Reduced
fertility primarily results from the further extension of
"childhood". However, it is probably more accurate to state
that reduced fertility results from continually delayed biological
reproduction post-sexual maturation. The continued
trend towards delayed biological reproduction was again
accompanied by a further intensification of parental investment,
and parents choosing to invest time and energy in the
"quality" of offspring as opposed to the "quantity" of offspring
[33].