(CNN) — Boys in the United States are starting puberty earlier than ever, according to a new study publishing in the November issue of the journal Pediatrics.
In the study, lead author Marcia Herman-Giddens from the University of North Carolina’s School of Public Health and her colleagues show that boys are starting to sexually develop six months to two years earlier than medical textbooks say is standard.
Researchers assigned each boy’s data to one of five stages — Stage 1 being pre-puberty, Stage 2 being the onset of puberty and Stage 5 being adult maturity. They then compared the ages and puberty stages of all the boys. The rigorous study was designed to report on only physical changes, not hormonal.
The results were broken down by race: African-American boys start hitting Stage 2 first, at about 9 years old, while non-Hispanic white and Hispanic boys begin developing around 10 years old. “This should have an impact on the public health community,” Herman-Giddens said.
But the researcher is concerned about using the numbers as a new standard for pediatricians. “That might be normal now,” she said, “but that doesn’t mean it’s normal in the sense of what’s healthy or what should be.”
One of the reasons she’s worried is that our environment may be playing a role in accelerating puberty.
“The changes are too fast,” Herman-Giddes said. “Genetics take maybe hundreds, thousands of years. You have to look at something in the environment. That would include everything from (a lack of) exercise to junk food to TV to chemicals.”
Sure it does:
(Non-Hispanic Whites, 1883-1919 cohorts from 1972-2010 GSS data, 1920-1930 cohorts from 1980-2010 data, 1940-1949 cohorts from 1990-2010 data, remaining from 2000-2010 data, restricted to ages 50+, 95% confidence intervals shown).
For Blacks, see here.
For those who don’t see the significance, IQ is related to r/K behaviors, such that lower IQ is associated with r-type traits such as earlier sexual maturation and more children (with less parental investment in each), and higher IQ associated with K-type behaviors such as later sexual maturation, fewer children, and greater parental investment in each child. With death rates lowered across the board, r-strategists have a reproductive—hence evolutionary edge.