Testing the Energetics of Gestation and Growth Hypothesis for Human Secondary Altriciality

Area of Science:

• Human evolutionary biology
• Primate reproductive strategies
• Developmental biology

Background:

• Human neonates exhibit secondary altriciality, a state of neurological immaturity coupled with high birth weight compared to other primates.
• The traditional obstetrical dilemma links this to pelvic adaptations for bipedalism, while the Energetics of Gestation and Growth (EGG) hypothesis proposes constrained maternal metabolism.
• Understanding the evolutionary drivers of human birth timing and neonatal development is crucial.

Purpose of the Study:

• To test the assumptions of the Energetics of Gestation and Growth (EGG) hypothesis regarding maternal metabolic constraints on human birth timing.
• To investigate the role of cortisol as a proximate trigger for birth under the EGG hypothesis.
• To re-evaluate the origins of secondary altriciality in humans.

Main Methods:

• Utilized empirical data on maternal metabolic scope and fetal growth to model hypothetical maternofetal dyads.
• Analyzed relationships between maternal and fetal patterns and birth timing.
• Examined the involvement of cortisol in human birth timing.

Main Results:

• No consistent correlation was found between maternal-fetal patterns and the timing of birth.
• Empirical evidence did not support cortisol's role as a proximate mechanism triggering birth in humans.
• The study questions the EGG hypothesis's assertion that metabolic limitations drive human birth timing.

Conclusions:

• Secondary altriciality in humans is unlikely driven by maternal metabolic constraints or cortisol as a trigger.
• The findings suggest that obstetric constraints, rather than metabolic limitations, play a more significant role in secondary altriciality.
• Human secondary altriciality may arise from heterochronic growth patterns linked to obstetric constraints, not solely shifts in birth timing.