Sexual Maturity: The Boys Are Catching Up With the Girls and its Killing Them

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It is a well-documented fact that girls are years ahead of boys when it comes to sexual maturity and development. Decades of medical records noting time of first menses have been used to measure and plot trends toward female sexual development with the resulting conclusion that girls are reaching menarche at younger and younger ages over time.

The problem with doing comparable studies with boys on sexual maturity is problematic. Documenting male sexual development such as the opening of the seminiferous tubules (where sperm are produced) and measuring increased testicular size are not practical indicators. Typically, sexual maturity is noted when a boy’s voice changes and an increase in aggressive behavior is observed.

As it turns out, this increase in aggressive behavior may turn out to prove to be a good measure of when boys reach sexual maturity. According to a recent study that follows the morbidity rate of young males, during sexual maturation boys reach an “accident bump” where the probability of a boy dying is at an earlier age today than in previous generations dating back to the mid-18th century.

The Accident Bump and Sexual Maturity

The “accident bump” is a euphemistic term that refers to a population-wide phenomenon of post-adolescent male mortality. From the time of sexual maturity to early adulthood, the rate of male mortality increases significantly due to risky behavior involving violence, accident and disease. This increase in risky behavior is attributed to increased levels of testosterone from the maturing testes.

It has been hypothesized that some non-human primate species also have an accident bump due to juvenile males reaching adolescence and then assuming a “high-risk, high gain” behavior that sometimes results in death. This is hypothesized to explain why the adult female to adult male ratio is high in some populations of Japanese macaques.

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Girls, as it turns out, do not have an accidental bump.

In a recent issue of the journal Plos ONE, Joshua Goldstein from the Max Planck Institute for Demographic Research describes his study where he applies statistical analysis using data from the Human Mortality Database. Census and death records were used to determine age-specific mortality rates from the European countries of Denmark, Sweden, Norway, United Kingdom and Italy. The focus of the study was to find the timing of the accidental bump when young male mortality reaches its highest peak. The data was compared in decade-long increments ranging from the mid-19th century to the present.

What Goldstein found was that the timing of the accidental bump has shifted toward a trend of an earlier age of sexual maturity for boys at a rate of approximately 2 months for every 10 years beginning as far back as the mid-18th century. An important parallel is that previous studies have shown that the rate of female sexual maturity has decreased with age at a rate of 3 months per decade. This essentially means that nutrition and health are the likely environmental causes that are allowing young bodies to mature more quickly over time.

One other finding was that although boys may be sexually maturing at an earlier age, they are not sexually-socially maturing earlier as well. The gap between sexual maturation and becoming a responsible adult who has finished college, found a job, married, etc. has broadened. In other words, it’s taking boys longer to “grow up.”

Concluding Thoughts on Sexual Maturity in Boys and Girls
According to the author of the study, as yet, unlike with girls and the inherent risks of early sexual activity, there are no clearly defined direct consequences for boys when they mature sexually early. Risk taking behaviors by boys will occur sooner or later whether it occurs at age 12 or age 16. The plus side may be that at an earlier age the boy will be under more parental control to monitor his behavior. The negative side is that the brain may not have developed enough to process risks that are too extreme. However, I would argue that there are clear risks for early male sexual maturation.

One problem is the legal/social ramifications of early sexual maturation. Violent crimes committed by younger criminals are problematic in multiple ways. Where do we draw the line between age and punishment? When is an adolescent no longer an adolescent? Should we try a youth’s mental maturity over his biological age?
When does the age of innocence end?

Citation: Goldstein JR (2011) A Secular Trend toward Earlier Male Sexual Maturity: Evidence from Shifting Ages of Male Young Adult Mortality. PLoS ONE 6(8): e14826. doi:10.1371/journal.pone.0014826

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