A new Northwestern University study of men in the Philippines makes a strong case for nurture’s role in male to female differences. For male infants, rapid weight gain in the first six months of life predicts a future where they will be taller, more muscled, stronger, have more sex partners and higher levels of testosterone than the average male.
The researchers, writing about their work in theProceedings of the National Academy of Sciences, speculate that testosterone may hold the key to understanding these long-term effects.
“Most people are unaware that male infants in the first six months of life produce testosterone at approximately the same level as an adult male,” said Christopher W. Kuzawa, author of the study. “We looked at weight gain during this particular window of early life development, because testosterone is very high at this age and helps shape the differences between males and females.”
Testosterone has long been known to increase muscle mass and put a person on a higher growth trajectory to be taller. This study suggests that the age of puberty is also influenced by events in the first six months of life. “Another way to look at it is that the differences between the sexes are not hard wired, but are responsive to the environment, and in particular to nutrition,” Kuzawa said.