Hormone levels in the womb may determine how masculine or feminine your facial features are as an adult, The Kids Research Institute Australia researchers have found.
The researchers, who used data from the Western Australian Pregnancy Cohort (Raine) Study, examined testosterone concentrations in the umbilical cord blood of 183 male and female newborns, taken 20 years ago, for the study.
Using sophisticated 3D technology, they then compared those results to facial images of the participants as adults.
The researchers discovered higher levels of testosterone in utero lead to more masculine facial features in later life.
"We used a computer generated algorithm to determine what masculine facial features were," the study's lead author, Professor Andrew Whitehouse said. "Generally speaking, men have wider foreheads, wider noses, longer noses and wider eyes, but this computer algorithm allows us to measure this with submillimeter precision."
"We found even within the sexes, individuals appeared more or less masculine depending on how much testosterone they were exposed to in the womb."
Professor Whitehouse said the data collected in this study provided the first direct evidence for a long-hypothesized link between prenatal levels of testosterone and adult facial features.
"It was previously thought that hormones during puberty were the main contributor to masculine facial features, however this research challenges that notion," Professor Whitehouse said.
"We now believe that differences in facial structure may be largely determined during prenatal life and testosterone surges during puberty simply exaggerate those existing differences."
The findings have been published in the journal Proceedings of the Royal Society.
The findings are the first stage in a broader study The Kids Research Institute Australia is conducting into the 'testosterone' theory of autism - the hypothesized link between exposure to high levels of testosterone in utero and autism.
The next step for researchers is to test children with Autism Spectrum Disorder to see if they have more masculine facial features.
If they do, it could provide evidence in support of the theory.
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