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It is widely believed that humans are the only animals to have an adolescent growth spurt, but new evidence from chimpanzees suggests this isn鈥檛 unique to us after all.

Some scientists define adolescence as being specific to humans because it involves social and cultural changes that are distinctly human experiences. Certain physical changes during adolescence, such as the growth spurt, also haven鈥檛 been seen in other animals.

The few studies that have measured limb development in captive primates found, at most, small growth spurts in height. But at the University of Texas at Austin says we don鈥檛 have enough evidence to draw conclusions about animals in the wild. 鈥淲e really have to be cautious making claims about human uniqueness without the relevant data,鈥� he says.

His team used an established technique for detecting bone growth that is reliable in humans, but that no one had applied to other primates: measuring levels of the proteins collagen and osteocalcin, which circulate in the body during bone growth. These biomarkers can be detected in blood and urine, so the test can be done non-invasively.

To collect samples, the researchers headed into Kibale National Park in Uganda, where they watched for chimps urinating. They pipetted urine from the ground or caught it in bags as it rained down from chimps in the trees. Since researchers have studied the chimp population in the park for nearly 30 years, Sandel and his team knew the age of each individual.

Back in the lab, they found that male chimps showed peaks in collagen and osteocalcin around puberty, resembling what happens in humans. 鈥淭his is showing that, somewhere in their body, their skeleton seems to be growing really rapidly,鈥� says Sandel.

However, the female chimps in the analysis didn鈥檛 show the same peak in growth signals. Sandel wants to collect more urine samples from females of a wider range of ages. It is possible, he says, that females have an earlier growth spurt.

But at Loughborough University in the UK questions how the study team has interpreted the results.

At puberty, male chimps grow their teeth, which they use to threaten each other in contests for mating or social dominance. 鈥淭he simplest reinterpretation is they are showing an increased rate of bone turnover in male chimpanzees, but I would say it鈥檚 due to eruption of large canine teeth and the supporting bones around the canine teeth,鈥� says Bogin. If so, the bone growth in chimpanzees might not be equivalent to the human growth spurt in height.

But Sandel says it is too soon to rule out a growth spurt in non-human primates, and that it is crucial to track physical changes, such as when the skeleton stops growing, in other animals. 鈥淭hat鈥檚 going to be key to defining the end of biological adolescence and beginning of biological adulthood,鈥� he says.