Sunday, 18 September 2016

Do Gorillas Have Culture?

Animal behaviour is generally instinctual. Their behaviour is, in some way, wired into their genetics, and doesn't vary from one animal to another. Particularly in mammals and birds, individual animals may be shaped by their life experiences, learning new things as they go. But what they can't do, as a rule, is pass that information on to others. Mothers may teach their young how to do certain things, but that teaching process is itself instinctual, so that all animals of a given species learn more or less the same thing as infants.

A large part of the success of our own species is down to our ability to circumvent this, to build on the knowledge of previous generations. This results, among other things, in the development of culture, differences in behaviour based not on the experiences of only one individual, but of their ancestors, in a way that isn't genetic. Britain and Japan are different culturally, not just because of environmental variation (Japan has earthquakes, for example, and has different mineral resources than Britain) but simply because of the vicissitudes of history, the separate evolution of their languages, and so on.

But we are part of the Animal Kingdom, and we didn't just come from nowhere. So, while the absence of language is obviously a fairly major constraint among non-human animals, it doesn't follow that they can't develop their own cultural traditions at some level. If mothers (for example) are able to learn new things, and pass them onto their offspring, we have the basis of "culture". Similarly if adults are able to copy others of their kind who they see employing new techniques to do something useful.

When we're talking about "culture" in non-human animals, what we're referring to are specific behaviours, found in some groups of animals but not others, when there's no obvious genetic or environmental reason why they shouldn't be. (For example, if a behaviour requires a particular plant, and that plant simply isn't available at some places, the absence of the behaviour there obviously doesn't count as "cultural"). The behaviour also has to be one that's capable of being learned, but it's generally proving that it isn't genetic which is the hard part.

Despite this, there are a number of animals where reasonable cases have been made for the presence of cultural variation across the species. Five years ago, I posted about spider monkeys, and there are also examples among capuchins, and, outside of primates, among dolphins, meerkats, and the dialects of songbirds. There's even been a claim of cultural learning among stickleback fish. But, in terms of both complexity of behaviour, and for its relevance to the origin of human cultural traditions, there's a particular interest in the presence of such learning among the members of own family, the great apes.

By far the most complex arrays of cultural traditions are found amongst chimpanzees, including variations in how they crack open nuts, or catch ants to eat. There is also evidence of cultural variation among orang-utans, and, to a much lesser extent, among bonobos. Which leaves a rather large, gorilla-shaped, hole in our understanding.

It's not that there isn't good reason to suppose that gorillas wouldn't be good at social learning. They're our third-closest relatives, after chimps and bonobos, they live in sizeable family groups, and their young grow and develop slowly, giving plenty of opportunity for such learning. The problem is instead simply one of geography. There have been several studies of gorilla behaviour, but almost all of them have been conducted at a single research centre in Rwanda (on which the film Gorillas in the Mist was based). It's only in the last decade or so that significant scientific study sites for gorillas have been set up elsewhere, and, in order to prove cultural variation, you need to be able to compare behaviour across multiple different geographic locales.

But now those new sites do exist, and have been existing long enough for the local gorillas not to be freaked out by the presence of humans, so that they act as they would if left alone. And, just a couple of weeks ago, the first study comparing the behaviour of gorillas at five different sites across equatorial Africa was published.

The study combines over 5,000 days of observations, taken over the course of several years at the different sites. They began by drawing up a list of 41 different behaviours that could potentially vary across the sites. It turned out that 18 of them didn't, unless there was some environmental reason why they just weren't possible at some locations. So, for those, there is no evidence to suggest that they might be culturally learned, and given the distances involved, fairly good reason to suppose that they might be instinctual.

That leaves 23 behaviours where there were significant differences between sites. Does that mean that these behaviours must all have been the product of cultural learning? Not necessarily. That's because we've known since 2001 that there are two different species of gorilla. The more widespread is the western gorilla (Gorilla gorilla), which inhabits the western part of the central African rainforests, while the eastern gorilla (Gorilla beringei) lives about 1500 km further east. Three of the study sites - in Gabon, Congo, and the Central African Republic - were inhabited by the western species, while the other two, in Rwanda and Uganda, were home to the eastern sort.

We know that the two species probably separated over a million years ago, perhaps when the jungles retreated during the Ice Ages. The history for the their subsequent interaction seems to be complicated, and they may have cross-bred as recently as 80,000 years ago. But, even so, if you're trying to rule out genetic explanations for different behaviour, the fact that the two groups of animal in question don't belong to the same species does rather limit your ability to do that.

About half of the remaining behaviours varied in this manner, being consistently seen in one species, but not the other. For example, female eastern gorillas readily groomed one another, while female western gorillas only ever groomed males. Equally, western gorillas often clap their hands together, while the eastern species does not.

Other behaviours were slightly more equivocal. For instance, the eastern gorillas at the Rwandan site frequently blew "raspberries", while those in Uganda very rarely did, and the western species didn't at all. But there are others where the differences within species are much clearer. Many of these were to do with play. For example, there's a game in which young gorillas chase one another round a tree; the Rwandan and Gabonese gorillas (which are of different species) both know this game, but the gorillas at the other three sites apparently don't. Similarly, gorillas at three sites regularly slap trees to make sounds similar to the ones they'd normally make by beating their chests, while at a fourth site it's rare, and at the fifth it's completely unknown. In none of these cases is there any obvious environmental reason for the difference; trees are in common supply wherever you get gorillas.

It is still possible to come up with explanations for this beyond cultural learning. The study noted that the more distant any two sites were from one another (even within the same species), the less likely they were to share traditions. Perhaps, one could argue, there is some genetic difference between the more distant populations. It would have to be one short of subspecies status, since, while there are multiple subspecies of gorilla, only one subspecies of each species was studied here... but it's not impossible.

On the other hand, one could perfectly well argue that greater distance also makes it harder to spread traditions down the generations as populations move - British culture more closely resembles that of Germany than that of Japan, for instance. So, at least to my mind, the cultural explanation does seem the more likely for at least some of the behaviours.

It's interesting to note that many of the traditions identified here are purely social; cultural conventions rather than specific techniques for doing something practical. This is not at all what we see in chimpanzees, where the traditions are usually either to do with preparing food or with some kind of tool use. Gorillas are much less likely to use tools than chimps in the wild, although it's obvious from studies of captive animals that they're intellectually capable of it. In this respect, they resemble bonobos, which tend to be far more interested in their social interactions than in the practicalities of tool use. The differences in traditions about who grooms whom is also interesting, and rather unexpected, since it's exactly the sort of thing that you'd think would be part of their basic social repertoire.

But it does seem to me that we can now answer the question in the title of this post with "almost certainly, yes." It's not as if some gorillas are developing baroque art while others are developing KanĊ, but there does seem to be a development of distinct habits in different groups for no reason other than mere happenstance, and that, after all, is the ultimate root of cultural difference.

[Photo by Richard Ruggiero/USFWS, in the public domain].

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