Updated | Hormones may not be the only factor responsible for the bodily changes that accompany the transition from child to teenager. New research shows that physical touch can also influence the onset of early puberty and the developing brain.
Researchers at the Bernstein Center and Humboldt University in Berlin wanted to better understand the role that such contact plays in triggering hormonal changes. So they designed a study that would allow them to observe just that. They housed young female rats in one of two ways: either with an older male rat or near an older male rat. This way, they could compare changes in the female rats sharing a living space with the male with those that occured in females that had a male within earshot—and nose shot—but not within fur shot.
According to the study, published in PLOS Biology by Constanze Lenschow and Michael Brecht, within a week, the 30-day-old female rats sharing cages with male rats developed the sex organs of more mature females. The genital cortex was much bigger on these rats compared to the females housed alone. The co-habitating females also experienced an increase in uterine weight and vaginal opening compared to their non-contact counterparts.
The researchers also wanted to know what would happen from touching the female rats' genitals artificially—meaning, in a way that would not normally happen. So they brushed the rats' nether regions with a lab instrument. Doing so expanded the growth of the genital cortex and accelerated the physical signs of puberty in the same way that hormones do.
Related: Puberty Comes Earlier and Earlier for Girls
"[T]he effects of sexual touch on puberty and the genital cortex are remarkable since you wouldn't expect this area of the brain to expand at this stage of development," Lenschow said in a statement.
The study provides supporting evidence that environment can influence sexual development. Previous research has found physical interactions and sexual touch can powerfully influence such development. In mice, adult males triggered the onset of female puberty with a combination of pheromones and physical stimulation.
These findings could have several implications for humans. In particular, adolescents who have been sexually abused or experienced inappropriate sexual contact could suffer detrimental physical consequences in addition to any psychological issues.
"Presumably the long-lasting problems from inappropriate sexual contact during development reflect brain changes resulting from sexual experience," wrote the researchers, in the study. Brain imaging studies in humans with a history of sexual abuse have reported comparably thinner genital cortices, for example.
The present findings are another reason to consider early-onset puberty as a potentially fraught moment for those experiencing it.
This article has been updated to add further clarity.
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