Sun, Aug 24, 2014 - Page 9 News List

Time running out for our cousins

As orangutans join a list of the world’s 25 most-endangered primates, scientists are finding that these great apes are more like humans than we thought

By Carole Jahme  /  The Guardian

Because flanged, or dominant, males will fight other males, sexually unreceptive females will also follow him to receive his protection from unflanged males who are likely to harass and rape unreceptive females. The study confirms that forward thinking is an adaptive trait in both sexes and not unique to humans, as previously thought.

As part of the Tuanan Orangutan Research Project, Brigitte Spillmann established that long calls can be used by listening orangutans to differentiate among males. Spillmann also found that the males’ long calls change according to the context. For example, one male might show off by noisily “snag crashing” — pushing over a dead tree — and another male will respond with a distinct long call.

Orangutans diverged from the lineage leading to humans, gorillas, chimpanzees and bonobos about 10 million years ago. They are the only Asian great ape and the only non-human ape with a fossil record. From it we know that archaic orangutans had bigger heads and far bigger teeth. The fossil record also suggests that 5 million years ago, orangutans spent more time on the ground and used more complex tools. It is thought that living in trees limits the tool use of modern orangutans.

“Orangutans are not more intelligent than chimps or bonobos in all domains, but they do have greater technical intelligence,” the University of Zurich’s Karin Isler said.

Male orangutans are three times the size of females. They also exhibit other ancestral traits of great apes, including rape, a lack of infanticide, extended lifespans (wild orangutans can live 50 years), and prolonged sexual intercourse. Orangutans and humans are more like each other than other apes in their prolonged, flexible and varied copulation postures.

Analysis of the genes for proteins in seminal fluid, associated with sperm competition in apes, has revealed that they are inactive in orangutans. This suggests that their mating system, which involves protracted mating with a single dominant male, did not alter after separating from the common ancestor of great apes. Prolonged intercourse among humans may also date back many millions of years.

It has been claimed that orangutan wrists are evolving a ball-and-socket joint, which would give them greater flexibility in the trees than they already possess and contribute to further divergence from other apes.

However, with habitat loss serving as their greatest enemy, safety may no longer be found high in the canopy. The uniquely human adaptations of long muscular legs, arched feet and Achilles tendons that enable running on the ground might help them more in the long term.

Female orangutans do not breed until 15 years of age, they have one baby at a time and six to eight years can pass before their next offspring. Combined with habitat loss, this makes the orangutan vulnerable to extinction.

At the upcoming October Convention on Biodiversity, the Sumatran orangutan is to be included in the list of the world’s top 25 most-endangered primates.

The orangutan is the only great ape with an annual international day, so stop buying palm oil products (a crop that encroaches on their habitats in Sumatra and Borneo) and consider “big upping” your endangered red-haired relative — and the new Sumatran species — while you still have the opportunity to do so.

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