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First they exposed them to new foods and plastic snakes and other novelties.
The ones who had spent their youth in the forest, learned the lessons of caution well. They didn’t try new foods, avoided the fake snake and in general showed the expected lack of curiosity.
Which makes sense. “Imagine you were dropped in the middle of a rain forest,” said Dr. Damerius. It would be unwise to touch all the plants, let alone pop them in your mouth.
But the orangutans raised by humans or brought to a rehab center at a young age experienced a relatively safe environment and human role models who were themselves curious. They were far more likely to eat the dyed purple rice or potato mush, and to investigate a fake snake.
In the second part of the experiment, the researchers used a variety of cognitive tests, requiring the apes to figure out how to open a box, or reach into a chamber in an awkward way to get a treat, or other tasks.
The more curious orangutans did much better.
Dr. Damerius said the research showed several things. It confirmed what is called the captivity effect, that time spent in a zoo or other safe environment promotes curiosity.
And it also showed that the younger the apes were when they spent time with humans the more curious they were. Orangutans that grew up in the forest did not have a big spike in curiosity from being at a rehabilitation center.
It also showed that curiosity helps in what are usually thought of as intelligence tests. “Curiosity is contributing to problem solving,” Dr. Damerius said. ”It increases the opportunities for learning.”
In addition, a species thought to be incurious turned out to be quite curious in the right circumstances. So this was a matter of environmental influence, not genetic endowment. She said it was “striking” that the different environment could elicit curiosity in orangutans. “I think there is this dormant, inherited potential.”
The findings do raise a question, she said, about what it means to release an orangutan with more developed curiosity back into the wild, where it may well be the unexamined snake that makes life possible, let alone worth living.
“When we realized that Batang Toru orangutans are morphologically different from all other orangutans, the pieces of the puzzle fell into place,” said Dr. Michael Krützen, a professor at the University of Zurich and a member of the research team.
Researchers then conducted what they called the “largest genomic study of wild orangutans to date,” comparing the genes from the recovered orangutan with data collected in the past from other field sites on Sumatra. They found that the Tapanuli population had become isolated from other Sumatran orangutan populations sometime in the last 10,000 to 20,000 years.
They also found that the Tapanuli’s orangutan’s lineage was ancient — between three and three and one-half million years old — and that they appeared to be direct descendants of the orangutan ancestors that crossed into what is now Indonesia and Malaysia from mainland Asia.
“We have learned how little we actually knew about orangutan evolution despite many decades of research and how much more there is to learn,” Dr. Meijaard said. “Orangutans are ancient creatures, as old as the very first members of our own genus Homo.”
Credit Tim Laman
The researchers acknowledged that there are limitations in their study, as they had access to only a single skeleton and two individual genomes. But they noted that other species have been defined with a single specimen.
Dr. Biruté Mary Galdikas, a Canadian primatologist who has studied orangutans for 46 years and led conservation efforts on the neighboring island of Borneo, said she was pleased – but not necessarily surprised – by the announcement.
“It was the talk 50 years ago, that there were two types, including one that had long fingers,” she said of descriptions made by residents of that area of Sumatra. .
“So what they have done is solidified the evidence, using anatomical evidence and genetic evidence, and evidence from the population.”
Dr. Galdikas, president of Orangutan Foundation International, said she hoped media attention over the announcement will further efforts to protect remaining orangutan populations in Borneo and Sumatra.
She also said she hoped it would spark new scientific debate on whether the three subspecies of the Bornean orangutan should themselves be elevated to full species of great ape, in particular the orangutan of eastern Borneo.
Mr. Slater could not be reached for comment, and his lawyer declined to comment. Jeff Kerr, the general counsel for PETA, said the group was pleased that Naruto would benefit from the images.
“The dire need of Naruto is what fully underpins why we pursued this lawsuit to begin with,” Mr. Kerr said in an interview. “We wanted every bit of all of the proceeds to benefit Naruto.”
It is not clear how much money will be directed to charitable organizations from sales of the image. Mr. Kerr said he did not know how much money Mr. Slater had made on past sales.
Mr. Slater, a freelance photographer, told The Guardian in July that he could not afford to fly to California from England for an appeals court hearing and was considering other sources of income. “I’m even thinking about doing dog walking,” he told the publication.
Naruto snapped the image during a 2011 trip by Mr. Slater to the nature reserve on Sulawesi, one of the few habitats for crested macaques, black monkeys with sloping faces and short tails. He mounted the camera on a tripod and set it to autofocus when Naruto approached, looked into the lens and pressed the button.
Mr. Slater published the photographs in his book, “Wildlife Personalities,” and fought with groups, including the Wikimedia Foundation, that used the image without permission. But the Wikimedia Foundation refused and said the photograph was in the public domain.
Copyright law in the United States grants ownership rights for images to the person who took it. PETA had argued that because Naruto was the rightful owner because he physically pressed the shutter button to create the image. But Judge William H. Orrick of the United States District Court in San Francisco disagreed and ruled in January 2016 that animals were not included in copyright law.
Mr. Kerr said that Naruto still lives in the Tangkoko Reserve, where he is fed daily by park workers and is a popular attraction. But crested macaques there are under constant threat by poachers, and the mammals are considered critically endangered.
Correction: September 12, 2017
An earlier version of this article mischaracterized the reason given by the Wikimedia Foundation for declining to remove an image of the monkey Naruto from its site. The company said that the photograph was in the public domain, not that Naruto owned it.