Nico was an adult male blue-diademed monkey living on a small island in the Quirimbas Archipelago in Mozambique. He was one of the few monkeys on the island with a name for one simple reason: all the individuals looked too similar to be identified individually. But Nico was different because his hand was completely atrophied. It looked as if his wrist had been caught in some kind of wire or rope that had cut off its blood supply.
He was also one of the first monkeys we met, as he was very used to humans. While most of his group of Cercopithecus mitis He would search for seeds on the ground, and he would come up to us and look at us expectantly. A few days later, we saw a man feeding him. Perhaps this tendency to approach humans was what caused his injury, or perhaps it was the other way around. We couldn’t know. Nor could he have survived in another place, where there were no humans who fed him from time to time or where there were predators.
But I couldn’t help but think that Nico was perfectly able to handle himself with one hand, and that there were no major differences between him and other males. The idea that natural selection acts as an unstoppable force can make us think that animals with physical disabilities have no place in the wild, and that only humans, by taking care of each other, have escaped this reality. But anyone who has spent enough time with primates in the wild knows that this doesn’t have to be the case.
Since the beginnings of field primatology, numerous anecdotes have been reported of primates with disabilities surviving for years. Even so, there are few studies that have delved deeper into this issue. That is why, in 2023, a research team from Concordia University (Canada), decided to analyze and collect all cases of disability in primates in a bibliographic reviewIn total, they examined 114 articles and found some general trends. Although many species are represented, chimpanzees and macaques are the most common, probably because they are the most studied. The vast majority of disabilities were physical and affected the limbs.
Once again, humans appear in the story. The authors of the review were struck by how frequently a link was found between physical disabilities in primates and environmental changes caused by humans. In particular, this was the case in 60% of the articles. A striking example is that which occurred in the Beza Mahafaly Special Reserve in Madagascar, where lemurs (Lemur catta) were losing their teeth early. In these primates, the hard tamarind fruit normally represents a small part of their diet. However, human disturbances in the reserve had reduced the availability of other foods and the lemurs had been forced to include more tamarind fruits in their diet, which wore down their teeth earlier.
However, toothless lemurs and other primates with different disabilities survive. How do they do this? The literature review suggests three reasons: flexible behaviour that allows them to adapt to the disability, the social environment and the potential to create new behaviours.
When lemurs lost their teeth, they spent more time feeding on hard fruit, licking it before eating it, they incorporated more leaves into their diet and they sought out fruit that had been partially processed by another lemur. This is a clear example of how primates are able to adapt to some anthropogenic disturbances thanks to flexible behaviour.
In terms of the social environment, the care of mothers in the first months of life is especially important. On Awaji Island (Japan), there is a population of macaques with a high rate of disabled people. Between 1978 and 1995, 14% of the offspring were born with some type of limb malformation. However, the vast majority survived past one year of life thanks to their mothers who were able to compensate for the disability by providing them with more care and adapting to the specific needs of their offspring.
One of these mothers was Yuki, one of the macaques with greater disabilitysince both of her hands were completely atrophied. She had learned to walk bipedally and to climb trees, she always chose those that had a structure of trunk and branches that allowed her to climb without using her hands. Her offspring was also born with a disability and could not hold on to its mother’s body, so Yuki carried it by pressing it against her body with her two malformed arms.
Special treatment of disabled infants is widespread among primates, with infant abandonment being extremely rare. Mothers of such infants have been observed to spend more time with them and remain in their proximity for a longer period of their infancy. They also wait for them when they are slower than normal, even if this causes them to lose contact with the main group, and guide them to food and water sources when they are blind.
Although less common, there have been reports of other members of the group helping the disabled. A macaque named Maki from Awaji Island adopted Meg, a seven-month-old disabled orphan. When he later became the dominant male of the group, he continued to let Meg accompany him and feed alongside him.
From disability to innovation
Finally, there have been quite a few reported cases of new behaviors caused by disabilities. Late was another macaque from the same group as Yuki, who He came up with a way to breastfeed her daughter Ribbon without much effort. Ribbon was born with malformations in both her hands and feet and could not hold on to her mother’s nipple. So Late would sit near a rock or tree and squeeze Ribbon between her body and the substrate so she wouldn’t have to hold her with her arms.
As Ribbon grew older and no longer depended on her mother for food, she also managed. Macaques use their hands to remove leaf litter and catch invertebrates; but Ribbon, lacking functional hands, He devised his own method. It hit the ground with its hands and feet to remove leaves and caught invertebrates with its mouth.
Sometimes novel behaviors spread throughout the group. Tinka was an adult chimpanzee from the Sonso community in Uganda who was paralyzed in both hands. Normally, chimpanzees use their hands to scratch their backs, but Tinka invented a different style. He held a vine outward with his foot and rubbed himself against it. It must have been a good way to scratch because before long, other able-bodied members of the group began scratching themselves. They started to imitate him. Using her ingenuity, Tinka managed to solve a personal problem and add value to the group.
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