Abstract
Relative to the life history of other great apes, that of humans is characterized by early weaning and short interbirth intervals (IBIs). We propose that in modern humans, birth until adrenarche, or the rise in adrenal androgens, developmentally corresponds to the period from birth until weaning in great apes and ancestral hominins. According to this hypothesis, humans achieved short IBIs by subdividing ancestral infancy into a nurseling phase, during which offspring fed at the breast, and a weanling phase, during which offspring fed specially prepared foods. Imprinted genes influence the timing of human weaning and adrenarche, with paternally expressed genes promoting delays in childhood maturation and maternally expressed genes promoting accelerated maturation. These observations suggest that the tempo of human development has been shaped by consequences for the fitness of kin, with faster development increasing maternal fitness at a cost to child fitness. The effects of imprinted genes suggest that the duration of the juvenile period (adrenarche until puberty) has also been shaped by evolutionary conflicts within the family.
Highlights
Will have been evolutionarily contested, with infants evolving to act in ways that marginally increase the time until the arrival of a younger sib
These findings suggest that expression of MKRN3 and DLK1, both paternally expressed genes (PEGs), inhibits pubertal progression — puberty occurs at a younger age if either gene is inactive — and that genetic variation at or near these loci is associated with normal variation in the age of puberty
The goal of this review has been to summarize current work in medicine, anthropology, psychology, and genetics that examines the complex transitions humans experience from birth to adulthood
Summary
“The tempo of human childhood: a maternal foot on the accelerator, a paternal foot on the brake.”. | | Received: 20 December 2017 Revised: 8 January 2018 Accepted: 18 January 2018
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