Some spider monkeys like a little something extra with "all this fruit"
Keith S. Taber
"oh heck, what am I going to do, I'm faced with all this fruit with no protein and I've got to be a spider monkey"
Primatologist Adrian Barnett getting inside the mind of a monkey
I was listening to an item on the BBC World Service 'Science in Action' programme/podcast (an episode called 'Climate techno-fix would worsen global malaria burden').
This included an item with the title:
Primatologist Adrian Barnett has discovered that spider monkeys in one part of the Brazilian Amazon seek out fruit, full of live maggots to eat. Why?
The argument was that the main diet of monkeys is usually fruit which is mostly very low in protein and fat. However, often monkeys include figs in their diet which are an exception, being relatively rich in protein and fats.
The spider monkeys in one part of the Amazon, however, seem to 'seek out' fruit that was infested with maggots – these monkeys appear to actively choose the infected fruits. These are the fruits a human would probably try to avoid: certainly if there were non-infested alternatives. Only a proportion of fruit on the trees are so infested, yet the monkeys consume a higher proportion of infested fruit and so seem to have a bias towards selecting fruit with maggots. At least that was what primatologist Dr Adrian Barnett's analysis found when he analysed the remains of half-eaten fruit that reached the forest floor.
The explanation suggested is that this particular area of forest has very few fig trees, therefore it seems these monkeys do not have ready access to figs, and it seems they instead get a balanced diet by preferentially picking fruit containing insect larvae.
Who taught the monkeys about their diet?
A scientific explanation of this might suggest natural selection was operating.
Even if monkeys had initially tended to avoid the infested fruit, if this then led to a deficient diet (making monkeys more prone to disease, or accidents, and less fertile) then any monkeys who supplemented the fruit content of their diet by not being so picky and eating some infested fruit (whether because of a variation in their taste preferences, or simply a variation in how careful they were to avoid spoilt fruit) would have a fitness advantage and so, on average, leave more offspring.
To the extent their eating habits reflected genetic make-up (even if this was less significant for variations in individual behaviour than contingent environmental factors) this would over time shift the typical behaviours in the population. Being willing to eat, or perhaps even enjoying, maggotty fruit was likely to be a factor in being fertile and fecund, so eventually eating infested fruit becomes the norm – at least as long as the population remains in a habitat that does not have other ready sources of essential dietary components. Proving this is what happened would be very difficult after the fact. But an account along these lines is consistent with our understanding of how behaviour tends to change.
An important aspect of natural selection is that it is an automatic process. It does not require any deliberation or even conscious awareness on behalf of the members of the population being subject to selection. Changes do not occur in response to any preference or purpose – but just reflect the extent to which different variants of a population match their environment.
This is just as well, as even though monkeys are primates, and so relatively intelligent animals, it seems reasonable to assume they do not have a formal concept of diet (rather, they just eat), and they are not aware of the essential need for fat and protein in the diet; nor of the dietary composition of fruit. Natural selection works because where there is variation, and differences in relative fitness, the fittest will tend to leave more offspring (as by fittest we simply mean those most able to leave offspring!)
Now he's thinking…
I was therefore a little surprised when the scientist being interviewed, Adrian Barnett, explained the behaviour:
"So, suddenly the monkey's full of, you know, squeaking the monkey equivalent of 'oh heck, what am I going to do, erm, I'm faced with all this fruit with no protein and I've got to be a spider monkey'."
Adrian Barnett speaking on Science in Action
At first hearing this sounds like anthropomorphism, where non-humans are assigned human feelings and cognitions.
Anthropomorphic language refers to non-human entities as if they have human experiences, perceptions, and motivations. Both non-living things and non-human organisms may be subjects of anthropomorphism. Anthropomorphism may be used deliberately as a kind of metaphorical language that will help the audience appreciate what is being described because of its similarly to some familiar human experience. In science teaching, and in public communication of science, anthropomorphic language may often be used in this way, giving technical accounts the flavour of a persuasive narrative that people will readily engage with. Anthropomorphism may therefore be useful in 'making the unfamiliar familiar', but sometimes the metaphorical nature of the language may not be recognised, and the listener/reader may think that the anthropomorphic description is meant to be taken at face value. This 'strong anthropomorphism' may be a source of alternative conceptions ('misconceptions') of science.
What goes through a monkey's mind?
Why 'at first hearing this seems like an example of anthropomorphism'? Well, Dr Barnett does not say the monkey actually has these thoughts but rather squeaks the monkey equivalent of these words. This leaves me wondering how we are to understand what the monkey equivalent actually is. I somehow suspect that whatever thoughts the monkey has they probably do not include any direct equivalents of either being a spider monkey or protein.
I am happy to accept the monkey has a concept somewhat akin to our fruit, as clearly the monkey is able to discriminate particular regularities in its environment that are associated with the behaviour of picking items from trees and eating them – regularities that we would class as fruit. It is interesting to speculate on what would be included in a monkey's concept map of fruit, were one able to induce a monkey to provide the data that might enable us to produce such a diagram. Perhaps there might be monkey equivalents of such human concepts as red and crunchy and mushy…but I would not be expecting any equivalents of our concepts of dietary components or nutritional value.
So, although I am not a primatologist, I wonder if the squeaking Dr Barnett heard when he was collecting for analysis the partially eaten fruit dropped by the spider monkeys was actually limited to the monkey equivalent of either "yummy, more fruit" or perhaps "oh, fruit again".