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| Orangutans in Sumatra's Batang Toru forest are now officially a new species: Pongo tapanuliensis. Credit: Maxime Aliaga/SOCP-Batang Toru Programme |
Not only is there great news about a new species of orangutan but the article in Nature announcing it quite casually shows how different strands of science all confirm current scientific understanding of evolution.
Firstly, the newly discovered orangutan (Pongo tapanuliensis).
Well, it's not exactly newly discovered so much as newly identified as a new species. It was first reported by western scientists about 50 years ago when they heard rumours of a population of orangutans living in a the Batang Toru forest in a remote part of the island of western Sumatra. However, it was not until anthropologist Erik Meijaard, that discovered the paper in the mid-1990s that scientists actually went looking for the population. They found the remains of a female, evidence of nests and a male killed by local people in 2013. From these, it was possible, using genetic evidence, to show not only that this was a new species, but how it relates to the other orangutans.
The newly-identified species has a flatter face, smaller heads and frizzier hair than their cousins in the northern part of Sumatra or in Borneo. There are also behavioural differences. The findings were published today in Current Biology.
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| Morphological Evidence Supporting a New Orangutan Species (A) Current distribution of Pongo tapanuliensis on Sumatra. The holotype locality is marked with a red star. The area shown in the map is indicated in Figure 2A. (B) Holotype skull and mandible of P. tapanuliensis from a recently deceased individual from Batang Toru. See also Figure S1 and Tables S1 and S2. (C) Violin plots of the first seven principal components of 26 cranio-mandibular morphological variables of eight north Sumatran P. abelii and 19 Bornean P. pygmaeus individuals of similar developmental state as the P. tapanuliensis holotype skull (black horizontal lines). See also Figure S2. |
Key to the determination was tracing the population’s ancestry. Surprisingly, Meijaard says, genetic testing of the Batang Toru skeleton revealed that the population is more closely related to Bornean orangutans, despite living on the same island as the other Sumatran group. That’s probably because of how orangutans migrated to the region, he says. All orangutans trace their origins to ancestors that lived on the Asian mainland about 8 million years ago. Those great apes migrated to what is now Sumatra, when sea levels were lower and the lands were connected. Genetic data suggest the Batang Toru species is the closest descendant of those first arrivals. The other Sumatran orangutans, which live in the island’s far north, split off from the Batang Toru group about 3.4 million years ago, modeling based on genetic data suggests. The Bornean orangutans also split from the Batang Toru group, but much later — about 674,000 years ago — which explains why those two populations are more similar, Meijaard says.
Climate evidence and the evidence of sea-levels, together with genetic evidence all come together to explain how this newly-discovered species is closest to the original which migrated from the Asian mainland when sea-levels were lower. The northern Sumatran group then split off from the Western group about 3.4 million years ago. Only much later, the Borneo group split from the western Sumatran group about 674,000 years ago - which is why they are genetically closer than are the two Sumatran groups.
The fact that so many strands of evidence mesh together to give a coherent explanation for an observed phenomenon is simply because science is right. If these different strands did not mesh so well it would be evidence of a flaw somewhere. Because science is a coherent whole and a description of reality, it would be astonishing it different disciplines were not mutually supporting.
The worry is that there are only about 800 individuals of this newly identified species in a single location, so it immediately goes onto the endangered species list and becomes the rarest and most vulnerable of out closest cousins, the great apes.
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