EVANSTON, Ill. --- It seems the old nature versus nurture debate can't be won. But a new Northwestern University study of men in the Philippines makes a strong case for nurture's role in male to female differences -- suggesting that rapid weight gain in the first six months of life predicts earlier puberty for boys.
Males who experienced rapid growth as babies -- an indication that they were not nutritionally stressed -- also were taller, had more muscle and were stronger, and had higher testosterone levels as young adults. They had sex for the first time at a younger age and were more likely to report having had sex in the past month, resulting in more lifetime sex partners.
The researchers think 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, associate professor of anthropology in the Weinberg College of Arts and Sciences and 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."
The study provides more evidence that genes alone do not shape our fate.
"The environment has a very strong hand in how we turn out," Kuzawa said. "And this study extends that idea to the realm of sex differences and male biology."
The study found men, on average, tend to be taller and more muscular than females, and the magnitude of that difference appears to be the result of nutrition within the first six months of an infant male's life, according to the study.
"There is a perennial question about how important heredity is versus the environment as shapers of who we turn out to be," said Kuzawa. "In the last 20 years, a lot has been learned about a process calle
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