And not merely because it is TGIF* day.

The theme “everything you know is sort of wrong” is familiar to readers on this blog. It is an underlying theme for much of what happens here. Every now and then that theme is manifest overtly, as in the Falsehoods posts, which are, as we speak, being revised, expanded, and reissued.

Well, starting this evening and running for an indeterminate amount of time (but probably a few weeks or so) “Everything you know is sort of wrong” is not just a phrase to keep in your head all the time as you are walking around doing stuff. It’s the name of a new radio show segment at Skeptically Speaking, with Desiree Schell.

EYKISOW is a short pre-recorded discussion between Desiree and me about the nature of falsehood in general and a specific falsehood (or two) in particular. Since it is not live, you can’t make snarky comments during the broadcast or call in, but you can certainly leave comments here or on other relevant blog posts and those comments could, in turn, influence future discussions.

So please join us today, Friday May 28th, 6PM mountain, 7 Central, on Skeptically Speaking:

…science blogger Greg Laden joins us for “Everything You Know Is Sort of Wrong,” a new regular feature exposing the truth behind some commonly held beliefs. Our first segment: Primitive Cultures.

The current batch of Falsehoods posts (Falsehoods II: Return of the son of the falsehoods that would not die) can be found here. The older falsehoods posts, pre-revision, expansion, and updating, can be found here.

But wait, there’s more! One of my favorite current books is Bonobo Handshake: A Memoir of Love and Adventure in the Congo by Vanessa Woods. Well, Vanessa is going to be the Main Guest on Skeptically Speaking tonight. So tune in mainly for that. Also, go to the Skeptically Speaking web site and turn on the chat thingie and make snarky comments during the show! It’s fun!

Details on Vanessa’s interview:

Journalist and author Vanessa Woods joins us to discuss her new book “Bonobo Handshake.” The memoir takes us inside Lola Ya Bonobo Sanctuary, a refuge for orphaned baby bonobos in the Congo. What can studying these highly social primates tell us about ourselves?

ADDED: The First Podcast is HERE.

footnotes

*Thank Gregory** its Friday.

**As in Pope Gregory XII, who gave us our current calendar.

One of the most important transitions in human evolution may have been the incorporation of regular food sharing into the day to day ecology of our species or our ancestors. Although this has been recognized as potentially significant for some time, it was probably the Africanist archaeologist Glynn Isaac who impressed on the academic community the importance of the origins of food sharing as a key evolutionary moment. At that time, food sharing among apes was thought to be very rare, outside of mother-infant dyads. Further research has shown that it is in fact rare … the vast majority of calories consumed by human foragers in certain societies and at certain times of the year comes from a sharing system, while the fast majority of calories consumed by chimpanzees is hand to mouth without sharing.

Nonetheless, sharing among adults in both common chimpanzees and bonobos does happen, and the patterns of sharing are slowly emerging as research progresses. It seems that most of the food shared among common chimpanzees outside of the mother-infant dyad is meat, and this happens to very variable degrees in different study groups. In some cases meat sharing is facilitated by socially aggressive begging. Individuals with a large part of a monkey carcass will eventually give others a tiny bit of access if they are annoying enough. In other cases, sharing of meat is argued to be nearly systematic, vaguely r resembling what human hunters do with the meat they garner. Meanwhile, the sharing of plant foods among adults is very rare in chimps, but much more common in bonobos (see White 1996 for a comparison).

A paper recently published in PLoS by Hockings et al, regarding the chimpanzees of Bossou (Republic of Guinea, West Africa), documents and discusses sharing of plant foods among adult chimpanzees in a particular context. Here, adult chimps …

…very rarely transferred wild plant foods. In contrast, they shared cultivated plant foods much more frequently (58 out of 59 food sharing events). Sharing primarily consists of adult males allowing reproductively cycling females to take food that they possess.

Why do they share cultivated food at a seemingly high frequency?

There are several factors that need to be considered in regards to sharing food. First is the overall potential for reciprocal altruism to arise in the context of foraging. Reciprocal altruism, which in theory need not rely on kin relatedness (but may occur in connection with it in real life) requires a number of conditions to arise, and all of these conditions apply to chimpanzees. For example, these organisms live a long time, frequently encounter the same other individuals on a regular basis, have a social system that would certainly allow for individuals to keep track of each other’s “altruistic” behaviors, and which would provide a facility for punishing cheaters. There are things to share (food) and it is presumably not difficult to imagine a mode of keeping track of values of exchanges as well. If vampire bats can share blood meals, then certainly one would expect chimpanzees to have the cognitive and social prerequisites for food sharing.

So in a way, one might rather ask: Why do chimpanzees not share food all the time? One major difference between chimpanzees and vampire bats (who regularly share blood meals after foraging bouts, among non-relatives) is the nature of the foraging itself. With the bats, there is a great variation from day to day (well, night to night, actually) in the amount of blood obtained, and there is a high probability of literally starving to death if one fails to obtain a sufficient meal for several nights in a row. Additionally, there is probably not a lot of individual variation in the bats themselves that accounts for the unpredictability … foraging success is simply a very random variable for them. In contrast, most adult chimpanzees manage to find sufficient food for themselves each day. When a given adult chimp is unable to find enough food, it is probably because there is a spatially broad seasonal shortage of food. In other words, all the chimps may fare purely or well in a given day, so the benefits of sharing food are typically low.

Another consideration related to sharing is “package size.” One of the null arguments (meaning, in this case, the argument that there is not really anything interesting going on) with the sharing of meat among chimpanzees is the package size argument. Most fruits are small, so you can’t share them, but meat comes in very large packages (compared to fruit). Therefore, no only can you share meat, but you might as well because there is no way you can eat it all yourself. The present paper does document a package size effect that may be part of the story: The main shared agricultural foods are large fruits.

There are some very large fruits native in the rain forest, but there is no clear systematically collected data indicating that these large fruits are shared. I studied the distribution and use of some of these fruits, and whenever I found evidence of chimpanzees eating them, the forest floor was always trampled down, with many sticks broken, lots of prints around, and fragments of the giant (water-mellon size) fruits scattered everywhere. Clearly, the chimps had had a party. Was it sharing? My gut feeling is no, but I have no idea how one would tell.

Another factor that the researchers seem to subtly indicate but do not explicitly state or explore (I suspect they had done so in earlier drafts but this is the kind of thing that would not make it past reviewers very easily) is that these fruits were not being gathered, but rather, hunted. A raid on an agricultural property is distinctly different from hand to mouth harvest of wild fruit. There are farmers who may be in inclined to shoot you or set dogs on you if you start messing with their fruit. The social value of items garnered in this context may be very different from regular wild fruit.

The researchers found that the majority of sharing among adults was adult males providing fruit to potentially reproductive females.

Sharing primarily consists of adult males allowing reproductively cycling females to take food that they possess. We propose that hypotheses focussing on ‘food-for-sex and -grooming’ and ‘showing-off’ strategies plausibly account for observed sharing behaviours. A changing human-dominated landscape presents chimpanzees with fresh challenges, and our observations suggest that crop-raiding provides adult male chimpanzees at Bossou with highly desirable food commodities that may be traded for other currencies.

Especially certain females.

Papaya raids occurred independently of the presence of females of reproductive age …. However, adult males shared crops – mostly papaya … overwhelmingly with these females (23 out of 25 sharing events with females…), particularly with one cycling female (14 out of 23 events;…) who took part in 83% of all consortships with males.

This female was apparently giving it out for papaya. It is possible that this entire phenomenon arises from personality (or would that be panality) traits of specific inviduals acting in unique and innovative ways. Such quirkiness and innovation seems to be a feature of well studied chimpanzee groups.

The second-ranking adult male, who shared most with this cycling female (43% of all her sharing episodes), was also her most frequent consort (50% of consortships) and grooming recipient (50% of her total grooming time). In comparison, the alpha male shared less frequently with this female (14% of all her sharing episodes), and despite his dominance, was less likely than the second-ranking male to consort (36% of consortships) and receive grooming (43% of her total grooming time) from her.

It will be very interesting to eventually work out the actual fitness consequences of this novel an rare behavior of sharing of raided agricultural crops.

Hockings KJ, Humle T, Anderson JR, Biro D, Sousa C, et al. (2007) Chimpanzees Share Forbidden Fruit. PLoS ONE 2(9): e886 doi:10.1371/journal.pone.0000886

Click here to see the original paper!

White, Francis J. (1996) Comparative socio-ecology of Pan Paniscus. In “Great Ape Societies” Edited by William McGrew, Linda Marchant, and Toshisada Nishida. Cambridge. Pp 29-41.

Research Blogging Citation:

Hockings, K.J., Humle, T., Anderson, J.R., Biro, D., Sousa, C., Ohashi, G., Matsuzawa, T., Brosnan, S. (2007). Chimpanzees Share Forbidden Fruit. PLoS ONE, 2(9), e886. DOI: 10.1371/journal.pone.0000886

See also this: Forbid Us Something, and That Thing We Desire

She was sitting there in class two weeks ago and exploded. She does not know that I know this, but I noticed it happen. Since she was sitting, as usual, in the front row, and it was all in her face, the other students did not see it but I definitely did.

By “exploding” in this case I mean that her brain suddenly filled with unanswered questions, which she then started sending me in frantic emails. Many of these questions are about things we will eventually get to in class, but some are on issues that we won’t touch on at all. I decided, and I received her kind permission to do this, to answer her questions by blogging them. This way I get to kill two birds with one stone, which is usually a good thing (unless of course you are the second bird).

In some cases I’ve re-written the question a little, but in all cases, they are good questions. I cannot guarantee that all of my answers will be good. But I do appreciate Marta’s inspiration, and find it inspiring myself. My only concern is that Marta gets interested enough in this material to become a biological anthropologist and thus wastes an otherwise potentially productive life. I’m hoping she becomes a doctor or a world leader instead, but we’ll see…

OK, on to the first question (I’ll deal with others in later posts):

Why did bonobos (Pan paniscus) evolve from common chimps (Pan troglodytes)?

The flippant answer is that we never really know or care why one species gives rise to another, we just see that it happens and document it. But underlying this question is the presumption that bonobos have interesting features that we do not expect to see in apes, and this is an opportunity to think interesting thoughts about evolution.

Bonobos are different from chimps in a few ways that we can presume are derived … meaning that they are novelties found in bonobos that arose as part of their differentiation from the common chimps, or subsequently. Since none of these features have a fossil record at this time it will be hard to say which known differences, if any, account for the speciation event itself.

The differences (that we’ll talk about now … this is not an exhaustive list):

• Bonobos have a female matriline in which dominance ranking of the females determines the dominance ranking of the female’s male offspring.
• The “chief bonobo” in a group is typically the highest ranking female. With chimps, most males are dominant over most females.
• Bonobos seem to have a lot of sex, and at least as interesting, they seem to have all kinds of sex, whereby all combinations of age, gender, and which body part is involved seem to occur except one: Males do not have sex with their mothers.
• Overall, there seems to be a higher level of agonistic (nasty) behavior among common chimps, especially involving males, while bonobos prefer sexual encounters over agonistic ones. One way of thinking of this is expressed on the Columbus Zoo web site: Chimps resolve sex issues with power; bonobos resolve power issues with sex.
• Bonobos probably live in larger groups. It is thought that having a large number of females in a group allows the females to dominate.

So, how, why, when, where, etc?

A key fact is that common chimpanzees have lived forever in a more or less continuous distribution (but there are important details of that I’m leaving out) across the breadth of the African Rain Forest north of the Congo/Zaire river, while bonobos live only south of the river. The genetic diversity and geographical range of the common chimps, and the fact that gorillas also live only north of the river, leads us to assume (this could be wrong but probably not) that at some point in time (about a million and a half years ago, maybe) a group of common chimpanzees somehow ended up on the other side of this river … a formidable geographic boundary … and subsequently gave rise to bonobos.

Richard Wrangham’s original hypothesis on this was that in the absence of competition for terrestrial herbaceous vegetation (THV), a major fall back food for chimps and THE major food for gorillas, bonobos were able to live in larger groups, leading to the large-number-of-females effect (see above) and thus ultimately to a totally different social system.

Subsequent studies by Wrangham and others have failed to show the expected difference in access to THV, thus probably falsifying this hypothesis. I’ve often thought that a very thorough study of all of the elements of the forest, not just THV, would show a number of candidate differences between the two regions (including other THV eaters, human hunter-gatherers, etc.), and I don’t think this kind of explanation should be ruled out yet.

However, there is another distinct possibility that should be considered, not necessarily as an explanation per se, but as a context for any explanation: I call this the “Fish or Cut Bait” phenomenon.

Imagine that there are two ways to do something, each of about the same effectiveness and of about the same cost. Or at least, the cost-benefit ratio of each approach is so close that you can’t say that they are different. In an evolutionary sense, either strategy could be an “evolutionary stable strategy” … one is not clearly going to invade and take over the other, in game theory terms … but only one will work at at time. They can’t both happen together in a given system. So it has to be one or the other. Fish or cut bait.

In this case, we have agonistic interactions to mediate social issues vs. erotic encounters to mediate social issues. For the former, how this works is obvious. Individuals perform nasty acts against each other, coalitions are formed, politics happen. This should be easy for any human to understand because this is the core of our own social system. Unfortunately. The latter may be harder to understand, but this also is part of our own social system as well (to a lesser extent) so we can relate to it.

In the case of agonistic (nasty) interactions, there is a psychological/emotional state that individuals strive for. Individuals are selected to do what it takes to not be in pain, not threatened, not stressed. You may do this by forming a tight coalition and the members of the coalition get left alone, occasionally groomed, not challenged very often. Or you might do this by avoiding the dominant individuals or coalitions. That’s all pretty obvious. Please don’t bite me, I wasn’t really looking at your girlfriend. Sure, you can have my banana.

But there may also be a state of being that one strives for that is accomplished by erotic interactions. It’s a temporary state of comfort or satisfaction that occurs through erotic interaction (including but not limited to “sex” … let’s not go into that definition too much. Here I mean sex to have babies, a behavior that is selected for regardless of the social dynamic, as opposed to all that other stuff bonobos do, which does not produce babies and is thus not selected for directly in relation to reproductive success).

Perhaps agonistic social politics and erotic bonding can each work about the same in the group dynamic of a medium sized frugivorous social ape. It is highly unlikely that either could work without interfering with each other. You can have a culture of general nastiness or a culture of erotic satisfaction. (I’m sure there are some who will say you can have both, but I’m pretty sure that is illegal in Minnesota.)

So now you have these common chimpanzees wandering around in a forest in which they or any other ape never before existed, because they somehow got across the Zaire river. I’m actually imagining that these come from a subgroup of chimps that lived in somewhat less forested environments, because they probably were the southeastern extension of the chimpanzee range, down south of present day Gombe, where they could stay in a forest and make it to the region south of the river, in times of maximal forest expansion during an interglacial.

As they move into the central forest south of the Zaire River, they find themselves in an environment that may have been richer than where they previously lived because of this shift from savanna-forest mixed habitat to true forest. (I quickly add that since chimps and fruiting trees probably have some important seed dispersal relationships, one might have to expect a difference in the distribution of key food sources, but let’s ignore that for now).

The point is that these are apes moving into a forest with virtually no conspecific or even congeneric neighbors against which to compete. In modern chimps, males spend considerable time and effort patrolling borders, and occasionally killing individual chimps from neighboring groups. According to Wrangham’s model of this behavior, the long term goal is to diminish the numbers of chimps in your neighboring group, so that if and when you need to expand your territory because of food stress, you can go over to the neighbor’s place, run them off and/or do them in, and at least temporarily enjoy a much expanded territory.

It is almost certainly true that day to day male agonistic interaction and the related coalition building in common chimps is essential for this strategy to work.

But these wandering chimps south of the big river, which would ultimately give rise to the bonobos, are expanding across an ape-free landscape, so this pattern is rarely selected for. Over several generations, in the absence of selection for the more traditional chimp-like social behavior, both the agonistic model and the erotic model of society are roughly equal in likelihood. We don’t need to postulate a specific reason why the erotic model emerged instead of the agonistic model. There would have been, according to this hypothesis, a roughly 50-50 chance of one or the other.

It is possible, though, that in this chimp-free landscape (at the outer edge of their range of expansion, at least) females could get into larger groups, and thus be more in charge. Since females will always lose in the agonistic model, but win in the erotic model, the erotic model was more likely to happen.

Every now and then I wonder about this question, not one that Marta asked: What would happen if a group of chimps and a group of bonobos, in the wild, found themselves as neighbors?

That would be the way it would happen if two chimps walked into a bar. Or imagine two chimps, and each finds a nice juicy bit of fruit out in the forest. And instead of eating the fruit, because they are not hungry, they carry it around for a while (this would never happen, but pretend) and then accidentally run into each other. What would happen? Same thing. Event though neither chimp actually needed the fruit and each chimp had its own fruit, the dominant chimp (between the two) would end up with both pieces of fruit.

This is why chimps could not possibly cooperate in any effort to scour the forest for various edible items, bring them all back to a central place, share and then cooperatively process the food items, and ultimately produce a meal that is eaten by all of the chimps on an as needed basis. Humans do that but chimps can’t. Explain this and you explain one of the major features of human evolution…

Some of us think that about two million years ago, an ape-like hominid ancestral population for humans gave rise to individuals with the novel capacity to do the following:

1) Make and control fire;

2) Cook food on this fire; and

3) Cooperate enough that individuals could in fact bring food morsels to a central place for processing and sharing.

The consequences of this nexus of novelties would be significant. There would be much more energy in the environment available for consumption because cooking converts a lot of inedible biomass into edible biomass. This could supply the necessary nutrients for bodies to grow larger and be maintained at larger sizes, which might be useful in the predator-rich environment of Africa. Note that where we can determine cause of death for australopiths, or at least guess reasonably what it might have been, predators are typically involved. This seems to stop happening with the larger bodied Homo erectus following this transition.

Another consequence is the extra nutrition to support the growth and maintenance of a large, costly brain.

These early human ancestors would have to have a way of cooperating rather than (almost) always competing over things like food. This could result in behaviors supportive of more complex and sophisticated technologies being regularly used, as we in fact see in the archeological record. The novel food sources plus the additional technology together would support this species’ movement into additional habitats previously not occupied by hominids. We also see this happening just at this time in the archaeological record.

For various reasons I won’t go into here, this would also have surely changed the overall social organization among these hominids, and we suggest that this may have been the origins of something not entirely different from modern (more or less monogamous) marriage.

(Here is a copy of a paper that discusses this idea in some detail.)