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This month, weâre looking at how wild primates, our closest living relatives, live with disabilities. This is a delicate subject, because there are a great many misconceptions, prejudices and tropes about disabilities, as well as about people with disabilities. As weâll see, these harmful ideas have carried over into research about animals with disabilities.
For instance, there are a lot of notionally inspiring narratives about people âovercomingâ disabilities. Such stories may seem benign to some, and they may be well intentioned, but they both flatten out the three-dimensionality of these peopleâs lives and erase people who for whatever reason donât overcome their disabilities.
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Itâs worth bearing this in mind as you read what follows, because there will be some stories in which animals manage to survive and thrive while living with a disability, and others in which animals with disabilities end up dead at a young age. These things all happened so are true in the most literal sense, but that doesnât mean either is the âtrue narrativeâ of animals with disabilities â let alone of people with disabilities.
With that in mind, letâs explore the lives of disabled primates.
Defining disability
My main source for this story is a , published in the American Journal of Primatology in December 2023. I spoke to two of its authors: and , both of whom are based at Concordia University in Montreal, Canada. They compiled 114 studies of physical impairments and disabilities in captive, free-ranging and wild primates. The studies featured 124 species, but chimpanzees, Japanese macaques and rhesus macaques were all overrepresented â probably because theyâve been extensively studied for decades.
The first challenge the researchers faced was specifying what they meant by a disability. It can be easy to tell if an animal has a malformation or injury, such as a missing limb, but this isnât necessarily disabling. That depends on the environment in which the animal lives, including its social environment.
In human society, disability rights campaigners talk about the social model of disability. The idea is that society, rather than a physical impairment, is what disables a person.
For instance, I have a physical impairment: severe short-sightedness. But this isnât remotely disabling for me because I live in a society where glasses are readily available. Similarly, people who use wheelchairs living in a society that provides ramps and other wheelchair-accessible ways to get around will not be disabled, but they can be if society insists on putting steps everywhere.
Stewart and Turner say the same is true for primates. âDetermining whether an animal is really disabled by their impairment is a whole challenge in itself,â says Turner.
With that in mind, the most frequent cause of disabilities was âmalformationâ, meaning a congenital condition that the animal had at birth. These accounted for the animals in 45 per cent of the studies. A further 24 per cent of the studies dealt with injuries and 23 per cent with illnesses or conditions.
The main thing that stood out to the team was how many of the disabilities and physical impairments were linked to human activities: fully 60 per cent. âThat was a big surprise to us,â says Stewart. âWe didnât think it would be that many.â Some of this comes from obvious threats like snare traps and gunshot wounds, but there were also instances of animals being burned by electric wires, poisoned by pollutants and infected by human-borne diseases.
Thriving in the wild
However, the biggest thing that leaps out of the data is that many of the disabled primates survived for many years. There are exceptions, particularly those born with really severe malformations â like a Japanese macaque that was seemingly born with no limbs. But on the whole, disabled primates seem to do pretty well.
âThe most striking thing that stands out, over and over again, is just how able physically impaired animals are to manage,â says Turner.
This may come as a surprise, especially if youâre steeped in evolutionary biology. We may think of nature as âred in tooth and clawâ, with natural selection ruthlessly pruning any individuals or species that arenât adapted to their environment.
âWhen I present this at conferences, I speak about that right away,â says Stewart. âI think thatâs the view that everyone has: survival of the fittest, youâre not going to make it with one arm in the wild.â
The thing is, it all comes back to an animalâs lifestyle and environment. As a rule, primates live in groups and get a lot of care from their mothers when theyâre young. Theyâre also highly intelligent and adaptable. As a result, even a major physical impairment like a missing limb need not be disastrous for a monkey or ape.
In line with this, the team identified 70 studies that looked at how primates behaved when confronted with disabilities. There were 45 studies describing animals showing behavioural flexibility. For example, some chimpanzees with paralysed legs would first move both arms forward, then swing their legs forward to meet them â a gait dubbed âcrutchingâ because it resembles the way humans walk on crutches.
A further 13 articles described disabled primates innovating: creating entirely new behaviours. A Japanese macaque called Ribbon, who had malformations of her hands and feet, fed by pounding her legs on the ground to disturb insects in the leaf litter, which she caught with her mouth.
Elsewhere, a disabled chimpanzee named Tinka devised a new way to scratch his back: he grabbed a hanging liana (a woody vine) with his foot and rubbed his back against it. Non-disabled chimpanzees later copied him.
Finally, 24 articles reported that disabled youngsters received more care from their mothers or other family members. You might imagine, on evolutionary grounds, that a female chimpanzee would ruthlessly abandon a disabled infant so as to have another child with a (supposedly) better chance of survival. However, the team says itâs âexceptionally rareâ for primate mothers to abandon their babies. The Japanese macaque born with no limbs survived for four months because his mother cared for him. Studies suggest primate mothers of disabled infants keep their babies with them for longer, are more responsive to their calls and lead blind infants to sources of food and water.Outside of family, other members of the troops seem to treat disabled individuals the same as everybody else. âPeople ask me, do the primates with disabilities get treated worse within the group, do they get excluded because of their disabilities, and we didnât find evidence of that so much,â says Stewart. âThey donât get extra benefits â itâs not like the other primates are like, âtheyâre disabled, weâll let them forage firstâ â but they also donât get excluded or really taken out of the group.â
This is a stark contrast to some modern human societies. People with disabilities were among the primary targets of the eugenics movement, which sought to imprison and sterilise people deemed unsuitable to breed â and which ultimately inspired the staggering horrors of the Holocaust. These ideas have lingered, even in our popular culture: it is distressingly common to see disabilities used as visual shorthand for evil in movies. The James Bond movies are atrocious for this, from the very first instalment, Dr. No, the villain of which is identifiable by his artificial hands, right through to No Time to Die in which the terrorist has facial disfigurements.
Thinking about all this led me to the question of prehistoric human societies and how hominins treated disabled individuals. We have much less information about this, because unlike living primates that we can directly observe in the wild, we have to infer everything about hominin behaviours from archaeological digs. And that means our preconceptions come into play.
Turner says that in the early 2000s, there was a big debate about disability in prehistory. It was triggered by the discovery of a jawbone from an unidentified hominin at a rock shelter in France. The , so the individual would have struggled to chew foods, leading to the suggestion that other members of the group cared for them.
However, âkind of debunked that ideaâ, says Turner, arguing that it was âa patronising view of people with disabilitiesâ. Remember, this was all based on a jawbone: we donât know anything about the rest of this individualâs body, let alone their behaviours. For all we know, they invented soup.
This isnât to say that caring for others isnât a key human behaviour, because it absolutely is. Thereâs evidence that benevolence, compassion and empathy are some of the traits that helped our species survive when other hominins died out, because they helped us build more interconnected societies.
But at the risk of moralising, the evidence from disabled primates should disabuse us of the notion that a disability means an awful or impossible life â because it doesnât have to be anything of the sort. âThereâs a lot of evidence that animals with disabilities, and probably ancestral humans with disabilities, were able to often do quite well, without necessarily receiving a lot of extra care or help,â says Turner.
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