The Southeast Asian rain forests orangutans call home are challenging environments, with unpredictable booms and busts in fruit, the animals’ most important food, said Tanya Smith, an associate professor in the Australian Research Center for Human Evolution at Griffith University and an author of the paper.
“When times are tough, adult orangutans will fall back on things like bark or hard seeds,” she said. “But offspring may not have the ability to eat some of these foods, or the knowledge to find them on their own, so they’re maybe falling back on mothers’ milk during periods of scarcity.” These are the first findings tying nursing to food scarcity in a primate, Dr. Smith added.
Previously, researchers estimated that orangutans wean off maternal milk between 6 to 8 years old, but they could never be sure because field surveys of the animals are tricky: Offspring often suckle inconspicuously, high up in trees or at night, and even when suckling is observed, it’s hard to know whether the animals are consuming milk or just comfort nursing, with no milk transfer.
To get around this, Christine Austin and Manish Arora, researchers at the Icahn School of Medicine at Mount Sinai, found a proxy for milk intake in orangutan teeth. Teeth are great for studying change over time because you can date them by growth rings, much like trees, Dr. Arora said.
When producing milk, mothers…