Tell Truths, Not Stories

On either side of a recent conference in London, where participants discussed the possibility that "human ancestors were exposed to a period of semiaquatic evolution", a number of voices have taken aim at the so-called Aquatic Ape Hypothesis. The AAH attempts to grapple with some interesting ideas, like why fish protein and fat is so important to our health, notably brain development, or why infants have an instinctual ability to swim, which disappears between 4 and 6 months. According to the mainstream theories of recent human evolution, these facts don't make a whole lot of sense.

It has been pointed out by many journalists (see the infamous Space Ape Hypothesis) that the AAH is still kind of ridiculous. Henry Gee points out the most crucial of flaws in the AAH, and more importantly, faulty underlying reasoning. For instance, sinuses, proposed to aid the theoretical Aquatic Ape in maintaining buoyancy underwater, are found in all mammals.

The AAH debate has been warmed over by a million people, both qualified and unqualified, over the course of decades. We don't need another tiny voice in that mix; I don't have anything to add about the AAH. But, the AAH represents much of what is wrong with evolutionary psychology, and points to a core issue that I've argued and discussed with many of my peers over the past several years: How do you make any progress in evolutionary psychology without creating a bunch of baseless just-so stories?

The short answer is, Slowly, and with a lot of hesitance.

When a psychologist found that that individuals who worry the most about social rejection are most likely to act out in response to rejection cues, what she found was truth. This is a fact of human psychology. There aren't any such facts about ancient psychology because we have no prehistoric psyches to work with, only archaeology, non-human primates, and modern humans.

What can we then say? Still quite a bit. Example: incest avoidance. Animals avoid mating with siblings and other close relatives because of the dangers of incest. There are many mechanisms spread across the kingdom that work to prevent incest from happening; in baboons, males disperse to a new troop to avoid reproducing with their relatives. In humans, we come to recognize those who we grow up in close company with as family members. This frequently applies to childhood friends of the opposite sex, and was a major problem for the sustainability for the Israeli kibbutz system. This is a psychological mechanism, born from an evolutionary need. It is respected enough to have been named. It is called the Westermarck effect.

Ultimately, the validity of evolutionary psychology lies with the validity of all science. If your findings aren't logically sound, other scientists will see through them, and you won't get published. Modern science has an additional tool: statistics, which allows us to falsify theories with varying degrees of confidence. Like any other field, statistics isn't perfected, but it is a powerful tool.

Unless your argument against evolutionary psychology is that all evolutionary psychologists are deranged, there is no particular reason to target evolutionary psychology. Evolutionary psychology is like psychology which is like all of science. There is fraud, there are charlatans, and sometimes just honest people get things wrong. We do what we can about that, but we don't disavow the entire field. 


If you would like to read more about the AAH itself, esteemed professors and bloggers John Hawks and PZ Meyers recommend that you go here. The site is more than just a discussion of the AAH, it is an informative primer for any interested in the logic of evolutionary psychology.

Ruminations on a conversation between primatologists

 A couple years back I had the privilege to hear Robert Sapolsky speak. It was a detailed talk, but given how much I know about his research already, there wasn't a huge amount of new information for me to learn. However, I did pick up on something he only briefly mentioned, and eagerly looked forward to asking him about it after the talk. I said to him:

"The baboons I've seen in the bush are very thin and spend almost all day every day foraging, so they have little time to engage in social interaction except mornings and evenings. You said that your olive baboons have the entire day to socialize; how is this possible?"

Dr. Sapolsky explained that the savanna his baboons live on is a paradise, ripe with easy to find food and moisture. Of course, other baboons could and do live under different conditions. But his baboons were lucky, and their fortune was certainly part of what made them such a great study group.

I haven't thought about this conversation much recently. That is, until I encountered a recent article in National Geographic. In this article, the author asked many of the same questions that came to mind when I heard Sapolsky speak: 'what on earth do these baboons feed on?…and where do they go to drink and sleep?'

Olive baboons are widely spread species in Africa, and while they are known to inhabit arid regions, the Chalbi Desert (the area discussed in this article) is dryer than most other such regions. I am most familiar with baboons sleeping in trees, but in wilder areas where there are more predators (notably leopards), high, steep cliffs are baboons' favored sleeping grounds.

I'm not sure that the authors of the Nat Geo article knew all of this (or much of any of it), but they may have found all the answers they needed, at least for this group of baboons. The troop in question spent a lot of time around doum palm trees, which provide water rich fruit, and shade. Apparently these baboons spend a great deal of the daytime in the doum palms' dense shade. I've seen baboons rest under cover during the heat of the day, but never to the extent found by the authors, in the Chalbi Desert.

These baboons don't live like Sapolsky's monkeys, that is for sure. Their environment does not seem to be able to sustain a large population, but it does seem to be able to support a small one consistently. All this speaks for the remarkable flexibility of baboons. They, like many other species of monkeys; chimpanzees and of course humans, can adapt themselves to survive (and possibly even thrive) in a myriad of different environments. They may not live the most healthy lives, but they will survive to reproduce, and keeps their genes alive.

Oh, and if you were wondering about the truth of Sapolsky story, well have a look at this.

Okay, you probably weren't doubting me, but I'm allowed to be boastful on occasion.

Vervets: the Forbidden Circle

I lied. The second article on vervets did not appear in Science, but in Current Biology. Other than that, I stand by my earlier statement: this is an unusual and thought provoking article, and it happens to be about vervet monkeys.

In this experiment, the authors created a locked container which contained appealing food. The subjects, a troop of vervet monkeys, could see inside and smell the food, but they could not get at it. Only a single low ranking member of the troop was trained in how to open the container.

Without needing to read the paper, I could tell you how things would start out. The dominant individuals in the group would mess around with the container, carrying out all kinds of violent acts in an attempt to force the thing open (which would all fail). Once the alpha got tired of this, it would go do something else and the second rank individual would make similar attempts to open the container. This is a common scene among the baboons, when they're trying to get into a locked storeroom or car.

In order for the monkeys to get at and eat the food inside the container, all dominant individuals would need to exhaust their own interest and wait. They were also required to stay a safe distance away from the container, somewhere between 10 and 15 meters. Only when the dominant individuals were a safe distance away would the monkey trained to open the container actually open the container.

It took most of these troops a few long trials to begin to understand that they would need to show restraint. But after they picked up this notion, the process went surprisingly smoothly and quickly, and the trained monkey would invariably be allowed to open the container. Unsurprisingly, the subject group that was experienced in raiding garbage bins and picnics took much longer to get over the fact that only a single low ranked individual could open the container. The authors go into great deal of game theory, but I will leave that by the wayside and get to the conclusions.

There are a number of fairly impressive accomplishments included in this paper. First, that the authors were able to train a wild vervet, to essentially be a confidant in their experiment. It is kind of incredible. Second, their main results show that these monkeys are capable of restraint on group and individual levels. Monkeys are notoriously bad at self-control, but this shows the power of reinforcement learning. I can't imagine any of the monkeys I've worked with, in captivity or the wild, being trained to show these levels of restraint. So kudos to the authors, and kudos to vervet monkeys.

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.

On Prairie Dogs

Not exactly my model species, but I talked about birds a short while ago, so why not prairie dogs? They're at least mammals with strong social organization. Anyway, I paper came to my attention, about dispersal in prairie dogs, and it was published in Science, so of course I had to read it.

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Prairie dogs disperse when all close kin have disappeared

Prairie dogs pull up stakes and look for a new place to live when all their close kin have disappeared from their home territory--a striking pattern of dispersal that has not been observed for any other species.

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Original article is here (behind Science's paywall). As previously discussed, baboons disperse when they are on cusp of full adulthood. They find a new troop, and usually stay with that troop until they die.

Prairie dogs differ from baboons in several striking ways. They live in large groups, called colonies, and the size of these groups can vary quite a bit, which is nothing unusual to a primatologist. But unlike baboons, prairie dop groups can range from five to thousands. Colonies can be further subdivided, into wards, and then coteries. Needless to say, prairie dogs almost certainly do not possess baboons' rich understand of who's who in the group. Nevertheless, these subdivisions are oddly reminiscent of the four-level hierarchy found in Hamadryas baboons.

Coteries are the closest thing there is a basic unit of prairie dogs. Coteries are sort of like harems: they consist of a male, several females, plus juveniles and infants. The juvenile males disperse soon after they are a year old. They leave their natal territory, settling about 1.5 miles away, on average. Females tend to stay put.

The author of this paper, Hoogland, references the esteemed Hamilton and May. Their theory was that dispersal occurs because reducing the amount of competition (for mates, food, etc) between related individuals is good for inclusive fitness. On the other hand, the potential for cooperation between related individuals might outweigh the costs of competition. Over the past few decades, Hamilton and May have been supported by findings in the field.

Hoogland has found contradictory evidence in his prairie dogs. When zero relatives are around, females are much more likely to disperse, 2.5 to 12.5 times more likely.

These prairie dogs have no opportunities for competition between relatives, but also no opportunities for familial cooperation. You might think that the dangers of dispersal would still be a major impediment, but apparently these populations live pretty close together, and the females usually just move one colony over, so the risks are low.

Hoogland's own words, to sum it all up:

"The absence of close kin in the natal territory is thus a proximate cause of natal dispersal by prairie dogs, but the ultimate cause is presumably the opportunity to find either a new territory that offers the benefits of cooperation with close kin that dispersed there previously (rare), or a new territory in which survivorship and reproductive success might be less dependent on cooperation with close kin (common)."

This may not be a study about primates, but the laws of dispersal and inclusive fitness govern all animals. When we discover a behavior violates our conceptions about how life must act in order to maximize fitness, there are two main possibilities:

1. The environment that this species lives in has given rise to a different approach to the challenge; unusual local factors are altering behaviors on the fringe.
2. The foundations of the behavior are not what we think they are. There are factors not being considered, which are crucial to understanding why these behaviors happen. Just because our model is correct most of the time, doesn't mean the model accurately represents why animals behave the way they do, in this case.

And anyone seriously studying this stuff ought to pause and consider new evidence in this light, if only briefly. In this case, the first option is probably at work. Prairie dogs are mammals, not so different from primates, but as Hoogland states, this is the first evidence of its kind, irrespective of species. Who knows, maybe a re-examination of dispersal behavior in primates will find similar evidence that's been overlooked. If you find it, chances are you'll get it published in Nature or Science.

Hoogland, J. (2013). Prairie Dogs Disperse When All Close Kin Have Disappeared Science, 339 (6124), 1205-1207 DOI: 10.1126/science.1231689

Dispersal Patterns

In this post, I want to discuss an important aspect of primate group behavior: dispersal. Most baboons spend their entire lives as part of a single group, with one main exception. As males approach adulthood, they will disperse, leaving their troop of birth to join a new troop, where they will (usually) spend the rest of their lives.

Female dispersal is rare, for dispersal is hazardous. Leaving the safety of the troop is a problem, but leaving the safety of known territory is also problematic. It's much easier to get away from a predator when you know the location of the closest tree. So why do primates disperse at all? For the most part, dispersal is the only way genes are exchanged between groups of primates. There must be some mechanism for individuals to change groups, or else inbreeding will become a problem.

Male baboons typically leave a troop around the age of 8 or 9. Leaving at that time benefits everyone: the males are strong enough to have a decent chance of surviving on their own (barring bad luck, which happens), the male will have better chances at mating and producing healthy offspring in another troop, and the female relatives of the dispersing male improve their own fitness by encouraging him to leave the troop and reproduce elsewhere.

Females will often refuse to mate with males born in their group, even if the female and male are not directly related. The male can force himself on the female, but that kind of behavior usually isn't worth the extra energy investment. If a male forms a mating pair with a female who doesn't want to be paired with him, she will be looking for any extra-pair copulations she can find, and the male isn't going to get any sympathy from the rest of the troop.

If a male isn't strong enough by age 9? He can usually stick around for a little while longer, but chances are he won't get much stronger, and at some point, the males and females in the troop are likely to let him know that he isn't wanted any longer. In all scenarios, the male will usually become ostracized if he does not leave.

Dispersal is difficult to study. Researchers have to follow young adult males, which is not particularly easy even when they stay within a troop. They need to stay close to the males, so they don't miss when they leave the troop, and then follow them through mostly empty bush, savannah, forest, until they join another troop. Little is known about the daily life of a dispersing male. As far as I am aware, no one has made a career of following dispersing males. Much of what we know has been observed by researchers following troops, who have tried to glean as much as possible from events where new males have joined the troop from outside.

Around the Cape, dispersal is a major issue because the baboons' natural predators have been removed from the ecosystem by humans. While in the process of dispersing, many males are caught by leopards or lions or hyenas. If a male isn't part of a troop, he will more easily fall prey, particularly if he is weak compared to other dispersing males. Without any large predators around, there is a higher male population, and usually not enough space among the existing troops to sustain all of them.

In the second troop, there has been a large influx of males more recently. Bopple seems to be hanging onto his status as alpha, but there have been as many as nine males in a troop of about 50. The troop is almost constantly in chaos. Males need to be able to keep apart from one another, and with that number of males in a single troop, it is simply impossible for them to keep distance between themselves. As a result, they chase each other, they chase the females, and they fight. It isn't a pretty sight. Watching male baboons face-off against each other is exciting, but it does get old, and that sort of volatility doesn't make data collection easy.

For additional reading, and more rigor (though I don't know how outdated their findings are, check out Alberts and Altmann, 1995.

Deadbeat Moms

Why some fathers get left holding the baby.

Scientists have cracked a 140 year old mystery as to why, for some animals, it’s the father rather than the mother that takes care of their young. Researchers from the Universities of Bath, Sheffield and Veszprém (Hungary) found that role reversal was caused by an imbalance in the numbers of males relative to females.

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Another paper published in Nature. This is exciting stuff, as the press articles say, this has been a mystery "140 years old", which is to say, as old as Darwin's work, since it has always been an irrefutable fact that the males of some species do sometimes help rear children. Many researchers have grappled with this problem over the past century and a half. Earlier work tended to appeal to ecological or life history explanations. 

Ecological theories suggest that the physical habitat which the animals inhabit drives males to be involved in the rearing of young. A theoretical example (solely for the sake of discussion): an environment turns dry due to drought, resources are scarce, and if a male and mate succeed in producing live young, the male would be drawn to invest in the infant because the chances of successfully producing more progeny is severely diminished. His energy is better spent helping out. 

Similarly, a life history explanation would suggest that as males age, their ability to compete with other males for mating rights with multiple females decreases. The alternative is to monopolize a female's time, and invest energy is making sure a small number of progeny reach adulthood. While these explanations may seem entirely plausible, the evidence simply does not support these theories.

Until now, thanks to the Liker et al's new theory. In the article's original title, the authors only claim to have answered the question in birds. It may be that no primate species are affected, that is, that role reversals in primates are not caused by an imbalance in sex ratio. Then again, there aren't many primate species in which the male ever takes over rearing for the female.

In many species, the males stick around, but do not get involved. In baboons, the males (and usually fathers) are ever present, but they don't engage in child rearing. They will interact with babies on occasion, but that is a far cry from rearing. Species in which the males play an active role in raising infants: owl monkeys and, of course, humans.

Humans are an interesting case, and not just because all my readers are human. When modern human males take over the rearing of children, is it caused by an imbalance in sex ratio? Probably not.
But then again, humans are not a good study subject for this sort of question; the environments we inhabit are not "ecological". However, our close relatives, chimpanzees and bonobos, do not engage in role reversals (nor do other apes), so the particular type of sexual role reversal we've evolved may be unique.

Liker A, Freckleton RP, & Székely T (2013). The evolution of sex roles in birds is related to adult sex ratio. Nature communications, 4 PMID: 23481395