Humans have a lot in common with chimpanzees but one thing we do not share is our level of social cooperation. Chimpanzees just don't care for each other like we do; on the contrary, they can be downright mean and vicious. What explains this? Well, one theory that's been developing recently is the idea that baby sitting is an important factor -- i.e., the fact that humans share child rearing.
Chimps and other animals that don't do it -- species where the mother is solely responsible for the infants -- also aren't as social or cooperative with each other generally. In contrast, species that do share child rearing with kin tend to be very, very social and show a lot of cooperation. They even show more altruistic behavior.
One similarity seemed to stand out: humans and marmosets are "cooperative breeders". Much more than most other primates, the adults of a marmoset group willingly protect and actively feed each other's young, usually without any prompting.
Chimps, in comparison, are independent breeders who will rarely help another's family. They are not even particularly giving to their own infants. "It's not like human mothers preparing meals for their kids, offering them food and letting the kids eat first," says Silk. "In chimps it's more that mum tolerates the kids taking bits. They don't usually get the best bits that mum would really like to have herself."
Van Schaik and Burkart began to suspect that the evolution of cooperative breeding might have paved the way for greater altruism more generally, and when they heard that anthropologist Sarah Hrdy of the University of California, Davis, had been thinking along similar lines, the trio decided to write a paper outlining their hypothesis (Evolutionary Anthropology, vol 18, p 175).
Their reasoning was simple enough: in groups that share childcare, the young need to be better at reading another's behaviour, to charm the adults and to recognise when someone might harm them. "The infants who are a little bit better at doing this are going to be those most likely to survive," says Hrdy. "Over generations you get directional Darwinian selection favouring infants who are a little better at mind-reading and a bit more inclined to quest for engagement with others."
Van Schaik and Burkart point out that shared childcare would also promote greater altruism in the adults, since proactive giving means the young don't have to call out in hunger to helpers, which could attract the attention of predators. This wouldn't be an issue for chimps as the infant is exclusively cared for by one adult--the mother--who is always right there and can attend to her infant's needs.
Source: New Scientist, March 19, 2011
Humans aren't the only species that cooperates to raise its young and the other species that do this provide further support for the thesis that such cooperation was fundamental to cognitive and moral evolution. Both dogs and elephants perform better than average on socio-cognitive tests and they both cooperate to raise their young.
Primates, though, do the best all around on all of this. Chimps may be awful at it, but there are other primates that do quite well with both cooperative raising of young and socio-cognitive tests: marmosets, tamarins, capuchins, squirrel monkeys, etc. It's really quite an interesting idea that has a lot of interesting evidence behind it.
The researchers think their hypothesis could go some way to explaining the roots of many more complex behaviours. "Cooperative breeding was the prequel to the main human feature film," says Hrdy, "and that is language, cumulative culture and high-level cooperation." For example, many cooperative breeders are also good at teaching. "As well as donating food, [they] donate information," says van Schaik.
Besides humans, very few other species are known to instruct others. Among the non-human primates, the best teachers are not the more cerebral apes, but the cooperatively breeding callitrichids. Adult tamarins, for instance, will at first bring infants dead insects to eat, but once the youngsters are old enough, they present live prey. Eventually, the helper simply indicates where an insect is hidden, leaving the youngster to make the catch for itself. "The helpers are highly sensitive to the ability of the infant," says Burkart.
The best-known teachers in the rest of the animal kingdom - meerkats, ants and birds called pied babblers--are all cooperative breeders too. "Many people think that for teaching, you have to be clever," says van Schaik, "but the simple rules meerkats use in teaching pups how to hunt scorpions, for example, shows that you don't have to understand what you're doing to be an efficient teacher." What you do need, he claims, is the motivation and skills that allow you to share information with others, which he believes come from cooperative breeding.
When you combine this motivation with the more advanced cognition of our ape brains, you begin to have the propagation of the complex skills that have marked human civilisation, van Schaik claims. This is important because influential innovations--like the invention of a new tool--come round very rarely, but with social learning, "they stick around and spread". The result, he says, is sophisticated culture and technology. A lot of research supports the idea that teaching is crucial for the evolution of culture (New Scientist, 20 November 2010, p 38), but cooperative breeding helps to explain why humans are so particularly good at it compared with the other apes.
According to the researchers, the social mindset afforded by cooperative breeding may have also set the stage for the evolution of language. Some rudimentary verbal skills might have evolved earlier in other intelligent species, like chimps, says van Schaik, except they just don't have the motivation to tell each other what's on their minds. With shared care, we feel the need to share information, he says, and we make declarative statements like: "Hey it's snowing out there, better come home early". "Chimps and orang-utans, they don't feel the need for that, but once you have cooperative breeding, the evolution of language is just expected," he says.
It's common for Christians to insist that morality and cooperative behavior are inexplicable without their god. In reality, though, the natural evolution of cooperative behavior can be found throughout the animal world. What's more, the natural evolution of cooperative behavior was probably key to our evolution as a species -- key to how and why we evolved with such extensive cognitive abilities.
It's natural, not supernatural. It's evolution, not any gods or ghosts.
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