Talk about parental dedication.
It's always been difficult to study the nursing behavior of arboreal primates like orangutans because their babies feed discreetly in nests. But a team of researchers studied orangutan teeth and found that they nurse longer than any other primate in the wild. Past research has found they suckle their babies for six or seven years.
But when fruit and other food sources are hard to find, young orangutans turn back to their mothers and supplement their diet with breast milk.
"And this pattern could last up until 8 or 9 years of age, which is very long," Christine Austin, an author of the paper and a researcher in the department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mt. Sinai, told NPR.
For the study, which was published in the journal Science Advances, the researchers measured the barium levels in the teeth of four orangutans that had died years earlier. During breastfeeding, the levels of barium, a nonessential element, are higher in the teeth.
"Teeth are like a biological hard drive that's recording what's happening in your body each day," Austin said.
The barium levels suggested that the babies drank only breast milk during the first year. Then they began to add fruit and other foods to their diet. But the orangutans continued to consume breast milk through their eighth and ninth year of life, probably when other foods were scarce.
Weaning the adolescent orangutans so late is likely a strategy to help them survive, Tanya Smith, the study's lead author, who works at the Australian Research Centre for Human Evolution at Griffith University, told NPR. "Having a long period of nursing may be a way for juveniles to learn the ins and outs of living in a challenging environment with limited and unpredictable food resources," she said.
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