Why are girls hitting puberty earlier? The answer could lie in the medicine cabinet.

Mothers who tested positive for chemicals found in common cosmetic products were more likely to have girls who hit puberty early.

  • American girls have been hitting puberty at earlier ages compared to past decades.
  • Chemicals found in common cosmetic products could be responsible for the changes, according to the results of a nearly 20-year study, which found that boys didn't seem to be affected by the same chemicals.
  • It's still unclear whether these chemicals cause early puberty, but it might be worth avoiding products containing them until the research is conclusive.

It's still something of a mystery why American girls have been hitting puberty at earlier ages compared to past decades. Finding the answer is important, considering early puberty is associated with health risks including depression, obesity, eating disorders and increased risk of breast cancer later in life. And though research suggests obesity and toxic stress likely affect the onset of puberty, those don't seem to fully explain the phenomenon.

Now, a new study published in Human Reproduction suggests another answer to the long-standing question: chemicals called phthalates, parabens, and phenols, all of which are found in common cosmetic products.

In 1999, researchers began the Center for the Health Assessment of Mothers and Children of Salinas study, in which they took urine samples from mothers who had been pregnant for about 14 to 27 weeks. The scientists then tracked the pubertal development of the resulting 179 girls and 159 boys, obtaining urine samples from the children every nine months between the ages of 9 and 13.

The results showed that the girls born to mothers who tested positive for diethyl phthalate and triclosan while pregnant were more likely to hit puberty earlier. Also, girls who showed higher concentrations of parabens–preservatives used in cosmetic products–were more likely to show early development of pubic hair and breasts, and also to get their period at a younger age. These effects occurred about one month earlier, on average, for every doubling in concentrations of parabens, as Inverse reports.

What do phthalates and parabens do to the body?

These chemicals could be jump-starting puberty because they're known as endocrine disruptors, which can interfere with hormones, such as estrogen, and cause changes in bodily development.

Still, it's too early to know exactly how phthalates and parabens might affect puberty in girls. The Center for Disease Control and Prevention says the chemicals aren't known to be dangerous in low levels, but notes more research is needed to determine their health effects.

One possibility is that it's the timing, not the amount, of exposure that influences bodily development.

"Many cosmetic companies argue that the level of a harmful chemical in any one product is not enough to harm you, on the basis of studies of chemical exposure in adults," the Breast Cancer Action organization says. "However, science is finding the timing of exposure is crucial, and that even a very small dose of some chemicals can have serious consequences in children and young women who are still developing."

If you want to be on the safe side, familiarize yourself with the various kinds of parabens and phthalates and try to only use cosmetic products without them. You can check out one list of such products here.

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  • The jaw bones of an 8-million-year-old ape were discovered at Nikiti, Greece, in the '90s.
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  • These fossils may change how we view the evolution of our species.

Homo sapiens have been on earth for 200,000 years — give or take a few ten-thousand-year stretches. Much of that time is shrouded in the fog of prehistory. What we do know has been pieced together by deciphering the fossil record through the principles of evolutionary theory. Yet new discoveries contain the potential to refashion that knowledge and lead scientists to new, previously unconsidered conclusions.

A set of 8-million-year-old teeth may have done just that. Researchers recently inspected the upper and lower jaw of an ancient European ape. Their conclusions suggest that humanity's forebearers may have arisen in Europe before migrating to Africa, potentially upending a scientific consensus that has stood since Darwin's day.

Rethinking humanity's origin story

The frontispiece of Thomas Huxley's Evidence as to Man's Place in Nature (1863) sketched by natural history artist Benjamin Waterhouse Hawkins. (Photo: Wikimedia Commons)

As reported in New Scientist, the 8- to 9-million-year-old hominin jaw bones were found at Nikiti, northern Greece, in the '90s. Scientists originally pegged the chompers as belonging to a member of Ouranopithecus, an genus of extinct Eurasian ape.

David Begun, an anthropologist at the University of Toronto, and his team recently reexamined the jaw bones. They argue that the original identification was incorrect. Based on the fossil's hominin-like canines and premolar roots, they identify that the ape belongs to a previously unknown proto-hominin.

The researchers hypothesize that these proto-hominins were the evolutionary ancestors of another European great ape Graecopithecus, which the same team tentatively identified as an early hominin in 2017. Graecopithecus lived in south-east Europe 7.2 million years ago. If the premise is correct, these hominins would have migrated to Africa 7 million years ago, after undergoing much of their evolutionary development in Europe.

Begun points out that south-east Europe was once occupied by the ancestors of animals like the giraffe and rhino, too. "It's widely agreed that this was the found fauna of most of what we see in Africa today," he told New Scientists. "If the antelopes and giraffes could get into Africa 7 million years ago, why not the apes?"

He recently outlined this idea at a conference of the American Association of Physical Anthropologists.

It's worth noting that Begun has made similar hypotheses before. Writing for the Journal of Human Evolution in 2002, Begun and Elmar Heizmann of the Natural history Museum of Stuttgart discussed a great ape fossil found in Germany that they argued could be the ancestor (broadly speaking) of all living great apes and humans.

"Found in Germany 20 years ago, this specimen is about 16.5 million years old, some 1.5 million years older than similar species from East Africa," Begun said in a statement then. "It suggests that the great ape and human lineage first appeared in Eurasia and not Africa."

Migrating out of Africa

In the Descent of Man, Charles Darwin proposed that hominins descended out of Africa. Considering the relatively few fossils available at the time, it is a testament to Darwin's astuteness that his hypothesis remains the leading theory.

Since Darwin's time, we have unearthed many more fossils and discovered new evidence in genetics. As such, our African-origin story has undergone many updates and revisions since 1871. Today, it has splintered into two theories: the "out of Africa" theory and the "multi-regional" theory.

The out of Africa theory suggests that the cradle of all humanity was Africa. Homo sapiens evolved exclusively and recently on that continent. At some point in prehistory, our ancestors migrated from Africa to Eurasia and replaced other subspecies of the genus Homo, such as Neanderthals. This is the dominant theory among scientists, and current evidence seems to support it best — though, say that in some circles and be prepared for a late-night debate that goes well past last call.

The multi-regional theory suggests that humans evolved in parallel across various regions. According to this model, the hominins Homo erectus left Africa to settle across Eurasia and (maybe) Australia. These disparate populations eventually evolved into modern humans thanks to a helping dollop of gene flow.

Of course, there are the broad strokes of very nuanced models, and we're leaving a lot of discussion out. There is, for example, a debate as to whether African Homo erectus fossils should be considered alongside Asian ones or should be labeled as a different subspecies, Homo ergaster.

Proponents of the out-of-Africa model aren't sure whether non-African humans descended from a single migration out of Africa or at least two major waves of migration followed by a lot of interbreeding.

Did we head east or south of Eden?

Not all anthropologists agree with Begun and his team's conclusions. As noted by New Scientist, it is possible that the Nikiti ape is not related to hominins at all. It may have evolved similar features independently, developing teeth to eat similar foods or chew in a similar manner as early hominins.

Ultimately, Nikiti ape alone doesn't offer enough evidence to upend the out of Africa model, which is supported by a more robust fossil record and DNA evidence. But additional evidence may be uncovered to lend further credence to Begun's hypothesis or lead us to yet unconsidered ideas about humanity's evolution.