The sobering fact of family law is that to be in the business of orchestrating

13.
Birth order/sibling presence:
Zajonc (2001, p. 523) reports
unambiguously that, “As the number of siblings increases, the
intellectual environment declines in its relative quality.” The
case for intelligence as a function of birth order is far less
compelling. Cross-sectional studies have traditionally suggested
that birth order affects IQ (Zajonc, 2001). Longitudinal studies,
however, suggest otherwise, clarifying only that larger sibling
groups deplete resources and may therefore be associated with
lowered IQ (Rogers, Cleveland, van der Oord, & Rowe, 2000).