A boy gaining weight faster in the first 6 months of his life will, as a young man, have more testosterone in him than his slower-growing peers, according to a study of more than 700 young men in the Philippines, Science magazine reports.
The long-term studies included 770 men from birth to adulthood. According to them, Science writes, boys who grow and gain weight more quickly reach puberty than children who gain weight more slowly. By the age of 20, they are stronger, more physically built and have more testosterone (and sexual partners).
Characterization as an adult male: Body size and sexual maturity are programmed through early experience, says lead author Christopher Kuzawa, a biological anthropologist at Northwestern University in Chicago, Illinois.
Researchers have long known that babies adapt to their environment before birth, and that this adaptation affects their physiology and metabolism as adults, including their risk of chronic disease.
Babies born to malnourished mothers, for example, will be born smaller and have a more efficient metabolism that requires less energy to survive. Babies whose mothers were well fed are often born larger and are more likely to grow larger and faster, needing more calories to support their larger bodies.
However, problems arise when babies with low birth weight are fed a diet high in sugar or fat that overloads their smaller organs, such as the pancreas, leading to diabetes, for example, Science writes.
Scientists are debating whether these body responses to bad and good periods in early development are adaptive adaptations to their environment. They claim that infants may have time windows in early childhood when they can improve their developmental trajectories. It is also possible that early nutritional neglect and stress predispose these infants to more disease as adults.
Kuzawa and his colleagues believe they will find evidence for the adaptive hypothesis in data on 770 men in the Philippines. It is part of a long-term research project exploring their development from birth. They found that boys who were breastfed had less diarrhea – possibly because they lived in higher-level hygiene homes – had faster growth rates for the first 6 months than babies who were bottle-fed or breastfed by poorer mothers.
Researchers noted that this is the period in which testosterone briefly rises to adult male levels, presumably due to the development of parts of the male body that consume a lot of the body’s resources, such as muscles, to develop. These boys reached puberty earlier, were taller and more muscular, and had higher blood testosterone levels as adults. Fast track male children often matured to have sex earlier, and reported sex more frequently.
Kuzawa hypothesizes that boys adapt to their environment by taking advantage of the features of early feeding. For example, men who are breastfed by well-nourished mothers learn more easily from the levels of hormones and nutrients in breast milk that they can live in a food-rich world and use the most valuable resources to accelerate their development, reach maturity and reproduce earlier. Men whose mothers gave them little nutrients or lived under stress grow correspondingly more slowly, saving their resources for survival in a poor world.
The authors show that the environment early in life has a lasting impact important to men, says evolutionary biologist Stephen Stearns of Yale University. Evolutionary biologist Peter Ellison of Harvard University disagrees with him, who does not think researchers have shown that early maturity in these boys is an adaptive response to their early childhood environment.
Differences in development reflect the genetic makeup of their parents and, for example, how sensitive different boys are to testosterone allows them to grow faster and be stronger, explains Ellison. (PAP)