Men who are tall, muscular and have high testosterone levels may be able to trace these traits to the nutrition they received the first six months of their lives, according to a new study.
The study researchers said nutrition affects testosterone levels in infants, and may hold the key to 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," study researcher Christopher W. Kuzawa, associate professor of anthropology at Northwestern University in Evanston, Ill., said in a statement.
The results are based on a group of 770 Filipino males, ages 20 to 22, who have been part of an ongoing study since 1983.
The researchers found that males who experienced rapid growth as babies an indication that they were receiving adequate nutrition were taller, had more muscle, were stronger and had higher testosterone levels as young adults than those who didn't undergo such rapid growth.
They also 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, according to the researchers.
"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," Kuzawa said.
The results weigh in on the nature-versus-nurture debate, the researchers said, by making a strong case for the role of nurture in differences between males and females and in the timing of puberty in boys. The study provides evidence that genes alone do not shape our fate.
"The environment has a very strong hand in how we turn out," Kuzawa said.
Testosterone has long been known to increase muscle mass and adult height, according to the researchers. The new study suggests that the age of puberty is also influenced by events in the first six months of life.
"Early experiences can have a permanent effect on how the body develops, and this effect can linger into adulthood," Kuzawa said. There is a lot of evidence that this can influence risk of diseases like heart attack, diabetes and hypertension -- really important diseases."
The study was funded by the National Science Foundation and the Wenner Gren Foundation, and was published today (Sept. 13) in the journal Proceedings of the National Academy of Sciences.