Sumatran orangutans have mystery ability to hold back puberty

Male orangutans are ready for reproduction around the age of 15, but they need to develop their secondary sexual characteristics such as cheek flanges on their face and increased muscle mass to attract a female.

However, orangutans in Sumatra island in Indonesia can delay attaining them for over 10 years, the researchers found.

This curious behaviour is something not seen in any other primate species, such as their cousins in nearby Borneo, said lead researcher Gauri Pradhan of University of South Florida.

The team also noticed that Sumatran chimpanzees, unlike their Bornean counterparts, would monopolise individual females for many weeks at a time, the Daily Mail reported.

Other characteristics that the males wait for include gaining longer hair on their arms and back, and larger throat pouches that allow them to produce long mating calls.

The researchers think that the two different types of adult males - those with secondary sex characteristics and those without - are two alternative mating strategies that evolved in orangutans.

Building up mathematical data, the team saw a correlation between the mating habits of the group and their arrested development.

Those troops where a few dominant males controlled all the females saw more incidents of orangutans delaying their development, until they had enough strength to depose the dominant males. At that point, with the coast clear, they would quickly reach sexual maturity, the researchers said.

However, how they are able to control their own growth is still a subject for debate, along with issues such as whether this is a conscious decision or otherwise, Pradhan said.

While the young orangutans seem to enjoy an extra 10 years as "children", using that time to built up their individual strengths, there is one large drawback -- early death, the researchers added.