Vervets: Flavor & Social Transmission

This week is vervet week. I have declared it. Coming from me, this means a lot, since I've never been particularly interested in vervet monkeys. But, two articles have been released in science recently: both on vervets, both so intriguing that I have been compulsively rereading them.

The first of these comes from Andy Whiten of primate culture fame. He has done impressive work in the past, and this latest vervet paper is an extension of that, though perhaps not the intuitive extension. The authors presented their wild vervet subjects with two types of food, varying two attributes of each type. First, the food was either colored blue or pink. Second, the food either tasted good, or tasted terrible.

Taste aversion can be found in pretty much all mammals; a type of learning that most humans are familiar with. By taste aversion, I mean that when you taste something bad you learn very quickly not to eat it again. Often it only takes one exposure to learn this, which in the animal behavior world is very very fast. Not only will animals learn to avoid foods that taste digusting, but they will also learn to avoid foods that they think made them sick, even if they didn't eat anything that tasted bad.

There is a broad literature on taste aversion in rats (a literature I happen to know pretty well), and in rats you will find even stranger, related phenomena. Rats possess the ability to socially transmit taste preferences through their sense of smell. They will actually smell the breath of other rats, and later, they will show a preference for food that smells and tastes like the odors they smelled on the other rat.

It turns out that vervets can do basically the same thing. The authors of this paper have shown that while vervets quickly learn to avoid the color of food that they know tastes bad, they can learn socially through watching other vervets to ignore their earlier preferences. For example, if a male vervet learns that pink food tastes gross, and then the male disperses to another group where everyone learned a long time ago that blue food doesn't taste good, the newcomer male will watch and learn to eat blue food, in spite of his earlier memories.

Rats possess a unique neurochemical mechanism for learning this kind of stuff, and cannot learn taste preferences socially. Yet this is exactly what vervets do: watch other members of their own species and using that information, learn new preferences and extinguish old ones.

To see this in vervets is striking. If someone reported these results in chimpanzees, it would not be particularly surprising because chimps are extremely smart and adaptive. Vervets are not great apes, not lesser apes, they're just old world monkeys whose brains are smaller than many other old world monkeys, notably macaques and baboons. If we see this kind of behavior in vervets, it really does suggest that this cognitive ability is fundamental in all old world monkeys.

Moreover, the authors refer to this type of learning as "cultural learning". I am not sure if I fully agree with this; the line between cultural and social learning is not clear. However, I would certainly say that this type of learning is at least an evolutionary antecedent to cultural learning.

van de Waal, E., Borgeaud, C., & Whiten, A. (2013). Potent Social Learning and Conformity Shape a Wild Primate's Foraging Decisions Science, 340 (6131), 483-485 DOI: 10.1126/science.1232769

Lip smacking and the origins of language

In a previous installment, I discussed gelada vocalizations and some new research specifically dealing with copulation calls. Thore Bergman, one of the same researchers who put together that paper, just published a short correspondence discussing a wide array of gelada vocalizations and their relationship to the evolution of human language.

This topic is been a tricky subject to approach because no primates' vocal range compares to humans'. The closest connection has been "lipsmacking", which is exactly what it sounds like: monkeys smacking their lips at each other without vocalizing. It very common among multitude of primate species.

Lipsmacking isn't a behavior that intuitively seems like it would have a connection to human language, but it turns out that the rate at which these monkeys smack their lips together is remarkably similar to the rate at which human lips open and close when they produce speech.

Gelada's take lipsmacking a step further. It turns out that they can produce a vocalization while smacking their lips together; it is called a "wobble". A as with lipsmacks, the rhythm of these wobbles is very close to the rhythm of human speech (between 3 and 8 Hz).

As I am fond of repeating, wobbles and human language are an example of convergent evolution. Baboons don't wobble. Chimps don't wobble. All of these species lipsmack. Even though the wobble is closer to language than the lipsmack, we just aren't that closely related to geladas, so the simplest explanation is that wobbles and language evolved independently from the same foundation, lipsmacking.

Have a look for yourself. Bergman provided a video in the supplement to his new publication, here.

Monkey Funk (or lack thereof)

Sea lion is first non-human animal to keep a beat

Ronan is the first known non-human mammal successfully trained to bob her head in time with a metronome-like sound — and then to apply her new skill to tempos and music she had not previously heard, according to researchers at the Long Marine Laboratory at the University of California, Santa Cruz.

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This is the biggest news in auditory (or at least musical) animal behavior, right now. Make sure you get to the bottom of the linked page where you will be rewarded with video evidence. It will be worth your while.

Reminds me of a similar, recent article featuring rhesus macaques. I was quite surprised to find that I had not previously written a post about said article. I won't let it by me a second time.

In this article, the authors describe results which suggest that macaques can detect rhythmic perception, but not beat induction (according to the earlier study, sea lions are the only mammal other than humans that can do both). The theory that there is a distinction between these two faculties is know as the dissociation hypothesis.

None of these terms are intuitively obvious. Beat induction is the ability to detect regularity of beats in a rhythm. It is what gives us our ability to tap our foot along with the beat in a song. Rhythmic perception merely refers to the ability to tell that some specific amount of time has passed. This sort of timing work has been studied extensively in many animal species, and it is well known that pretty much all mammals can time intervals. In fact, I have myself done some work demonstrating rhesus macaques' flexibility in timing intervals (Diapadion et al, unpublished results or something).

There is a major drawback to this monkey study: there is no behavioral data. It is entirely EEG. In many ways, I prefer EEG to fMRI or electrophysiology for brain imaging. EEG takes a distributed look at the activity of billions of neurons, unlike eletrophysiology, where you isolate signals from single neurons and pretend that the entire brain region surrounding acts the same way. fMRI also takes a distributed look at brain activity; in fact it is often more accurate than EEG. Unfortunately you can't put monkey into a MRI scanner unless the monkey has been knocked unconscious. You have to stay still in the scanner to get good data, and monkeys, well, they're not so good at that, ever.

fMRI is also superior to EEG because fMRI allows you to see deep into the brain, whereas EEG only lets you look at surface areas because it is on the surface of the skull that you place the EEG electrodes. There might be something going on deep in the auditory cortices that the authors' EEG findings are missing. Which is why it would be nice to see some results from additional metrics. Practically speaking, I don't believe it is likely that the authors are mistaken; the primate literature supports their hypothesis.

In the sea lion video, the speaker suggests that beat keeping may be far more widespread in the animal kingdom than previously thought. No, probably not. This EEG study suggests that monkeys are totally incapable of beat induction, and it stands to reason (and evidence) that this holds for other primates. As it stands, convergent evolution is the most likely explanation.

Honing, H., Merchant, H., Háden, G., Prado, L., & Bartolo, R. (2012). Rhesus Monkeys (Macaca mulatta) Detect Rhythmic Groups in Music, but Not the Beat PLoS ONE, 7 (12) DOI: 10.1371/journal.pone.0051369

Old Drifters

Since reading and writing about prairie dog dispersal, my thoughts have returned to some odd events which took place among the baboons some time ago.

I wrote about these occurrences in a some old posts. To summarize: two old male baboons, Chester and Mortimer, both moved from the main troop to the second troop, higher up on the mountain. In Chester's case, he was following Eunice, his favorite female. Mortimer's motives were less clear. Eventually, both returned to the main troop. This was not the first time the older males have pulled stunts like this, and it won't be the last. Although, there won't be many more opportunities for these two in particular. They're getting pretty old.

At the time, I wondered if there were any examples of behavior like this in the literature. The prairie dog article sheds some fresh light on these baboons' behavior. I don't think these baboons are dispersing for the same reason as prairie dogs, but I think it is likely that mid to late-life dispersal may be more common, and perhaps systematic, than researchers have been inclined to believe.

For my baboons, the odd origin of these troops (they were all one big troop many years ago when the population was smaller) muddies the water. These behaviors might not even be valid dispersals. However, it is difficult to say if these males would leave the area if they had the option, for baboons in Tokai can't disperse beyond the forest without encountering serious resistance from human populations. Or, as I am fond of considering, they might just be outliers.