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Book notice: Stephen J. Gould’s The Panda’s Thumb

A used copy of Stephen J. Gould’s book The Panda’s Thumb (1980) has been sitting on my shelf for a while, and I’m kicking myself for not reading it sooner. What a delightful little book of science essays! Each essay is an edited version of one of his monthly columns at Natural History magazine. Subsequently, the essays are intelligible to the general intelligent reader, but Gould does not thereby sacrifice an appreciation for hard facts and subtle reasoning. Gould makes science come alive with his anecdotes, wry humor, and gentle argumentation about topics ranging from the panda’s thumb to hopeful monsters and everything in between. Nothing is too big or small for Gould to think worthy of writing about. All in all, I highly recommend this book for any student of biology or lover of science.

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Why Us and Not Them? A Review of Sarah Hrdy’s Mothers and Others

“Thou hast no sense. You French people love your own children; but we love all the children of our tribe.” ~Naskapi tribesman

Sarah Hrdy has done the field of evolutionary psychology an inestimable service by writing Mothers and Others: The Evolutionary Origins of Mutual Understanding (2009). First and foremost, Hrdy has contributed to the advancement of a burgeoning field by bringing together a large and diverse assortment of cutting-edge empirical work in one volume. Second, Hrdy’s deep familiarity with recent work in primatology and cross-cultural anthropology provides a helpful constraint on evolutionary speculations about the human “Environment of Evolutionary Adaptedness” (EEA). Insofar as Hrdy’s book can be seen as a plea for sociobiology to go beyond weakly substantiated speculation about our ancestral way of life, it deserves attention by anyone interested in the origins of human cognition.

The first chapter kicks off with a provocative thought experiment. Hrdy points out that we take it for granted just how well humans get along when stuffed on an airplane with three hundred cranky strangers.  But imagine the same airplane crammed shoulder-to-shoulder with chimpanzees. The inevitable bloody mayhem stands in stark contrast to the overt politeness usually governing human strangers. Hrdy now asks the central question of the book: Why us and not them?  That is, why do humans get along so well with each other but chimps don’t?  Hrdy says “The goal of this book will be to explain the early origins of the mutual understanding, giving impulses, mind reading, and other hypersocial tendencies that make [riding airplanes] possible” (p. 4).

Hrdy catalogues several traditional answers where the difference between humans and chimps has to do with our big brainy intelligence. After arguing the fossil record paints a different story,  Hrdy chastises such overly “intellectualist” stories for putting the cart before the horse and instead favors a hypothesis recently argued by Michael Tomasello (Herrmann et al., 2007; 1999): “The crucial difference between human cognition and that of other species is the ability to participate with others in collaborative activities with shared goals and intentions” (p. 9). Why are humans so “ultra-social” compared to chimps? It obviously won’t do to point to the existence of special human capacities like our ready disposition for empathy because that only pushes the question back further: why do humans have such capacities but chimps don’t? Given that natural selection is blind to possible future benefits, there must have been some “initial payoff” for developing such social-cognitive competencies. Clearly we will need to give an “ultimate” evolutionary explanation for the origin of our uniquely human social-cognitive competencies that outlines a plausible fitness payoff.

In the second chapter, Hrdy reviews contemporary evolutionary accounts of our social-cognitive capacities and finds them lacking. A popular theory is to claim that increased intersubjectivity would have been adaptive for a  group of social primates, particularly with respect to “intergroup conflict” (Choi & Bowles, 2007). However, Hrdy asks “How much sense would it have made for our Pleistocene ancestors eking out a living in the woodland and savannas of tropical Africa to fight with neighboring groups rather than just moving?” (p.19)[1] Moreover, Hrdy is skeptical of these hypotheses for a more general reason. She asks,

If intersubjectivity was so useful for maintaining cohesive social groups, defending one’s in-group from violent neighbors, or wiping out competitors, why didn’t other social primates (those ‘demonic neighbor-stalking chimpanzees in particular) evolve such gifts as well? (p. 37)

Hrdy applies a similar logic to other evolutionary accounts such as the Machiavellian Intelligence hypothesis or the hypothesis that humans are special because we have mirror neurons. For Hrdy, most hypotheses on the table either fail to answer the question, “Why us and not them?” or they rely on empirically false claims about the abilities of chimpanzees (e.g. the false claim that chimp infants cannot imitate or follow eye-gaze, see p. 58). Hrdy’s ultimate diagnosis of all these false starts is that they mistakenly used the chimpanzee model as a basis for theorizing about our human ancestors. Hrdy’s prescription is to turn to recent developments in primatology and cross-cultural anthropology to study how human childcare in extant hunter-gatherer societies works, and from there find an appropriate primate model to make inferences about the EEA.

The third chapter in a nutshell is Hrdy’s defense of the old expression “It takes a village to raise a child”. Indeed, Hrdy’s overall answer to the central motif of the book is that the  selection pressure for human competence in social cognition arose due to novel rearing conditions approximately 1.8 million years ago where youngsters depended on more people than just their parents for care. Hrydy proposes that these “alloparents” like sisters, aunts, grandmothers, and even extended exchange networks involving non-paternal males were the crucial link in the evolutionary story. If a child’s survival in the EEA would have been affected by the availability of alloparental care, then there could have been selection pressure for infants to develop the mental resources to decode the mental states of others in order to illicit extra-parental help. As Hrdy puts it, “the need for alloparental succor transformed the selection pressures that shaped our species, and in doing so altered the way infants developed and then the way humans evolved” (p. 67). Although she acknowledges a possible role for intergroup competition in shaping our prosocial attitudes (p. 20), Hrdy believes many researchers have overlooked the crucial importance of child-rearing and have not sufficiently thought about the difficulty of ensuring the survival of helpless, slow-maturing children in the wild.

To support her hypothesis, Hrdy turns to primatology data (some of which she collected herself) to examine patterns of mother-child care in Great Apes. The most salient finding is that Great Ape mothers under no circumstances ever hand over the infants to another caretaker (even sisters eager to practice their parenting skills). This stands in sharp contrast to modern hunter-gatherer societies where “mothers trust others and allow them to take their infants shortly after birth” (p. 78), a form of child-rearing known as “cooperative breeding”. According to Hrdy, humans are not the only cooperative breeders, a distinction also shared by a family of New World monkeys called the callitrichids, of whom the marmosets are a representative example.[2]  Although humans are cognitively similar to chimps in many ways, it is these “dumber” yet socially sophisticated New World monkeys that may provide the best primate model for reconstructing the EEA in virtue of their shared emotional proclivity for prosociality and cooperative breeding (Not to mention the sociality seen in bonobos, who are genetically equa-distant from humans as chimps).

In the fourth chapter, Hrdy takes up the popular 20th century framework of “attachment theory” and updates it in light of recent developments in the study of alloparenting in human societies. John Bowlby, the founder of attachment theory, famously modeled the mother-child attachment relationship on the iconic notion that the mother and child were inseparable, just like chimp mother-infant relationships. Reviewing both old and new data, Hrdy concludes that modern research on attachment formation overwhelmingly suggests that the development of healthy social attachments depends crucially on forming bonds with nonparental caretakers. Indeed, “infants nurtured by multiple caretakers grow up not only feeling secure but with better-developed and more enhanced capacities to view the world from multiple perspectives” (p. 132). And in essence, since children with reliable alloparental care would have had access to more calories and care-taking resources, they would have survived better than those who didn’t, thus generating an adaptive selection pressure for the development in infants of the mind-reading capacities necessary to solicit help from others.

The fifth chapter takes on standard evolutionary theories of parental investment and considers the potential role of fathers in successful childrearing. A standard story might be that because females rely on the assistance and resources of fathers to raise their children, the practice of pair-bonded monogamy arose due to a tacit “sex contract” between males and females. In essence, the contract states that in return for parental investment, the females will “exclusively” offer the male sexual access. But Hrdy wonders what happens when the “loving father” is not around to help? Could alloparents step in? In light of paleoanthropological data concerning the relative infrequency of male hunters scoring meat in the Pleistocene, as well as numerous anthropological data describing the strong egalitarianism of hunter-gatherer tribes (sharing the spoils of the hunt with nonkin during large communal feasts), Hrdy says “It’s clear that the most successful hunter would often get no more for his family than the most hapless did” (p. 149).  Here Hrdy approvingly cites Kristen Hawkes’  “show-off hypothesis” (1991) where the benefit of successful male hunting was cashed out more in terms of prestige and reputation rather than pure caloric load distributed to kin. Accordingly, it is the hard work of female gatherers that probably made the biggest daily caloric impact on the survival of children. And if such females could form matrilinear coalitions for cooperative breeding, an inflexible sex contract to secure caretaking resources would have been unnecessary,  leaving room for more flexible parenting (and mating) strategies, including ones where the males don’t offer care exclusively to their kin (which is not to say fathers would place equal weight on nonkin, see p. 157)

As Hrdy puts it, “At the heart of the [sex contract] model lay a pact between a hunter who provided for his mate and a mate who repaid him with sexual fidelity so the provider could be certain that children he invested in carried at least half of his genes” (p. 147). Hrdy doesn’t deny the existence of sexual jealously and male concerns about paternity, but Hrdy’s moral is that “A fixation with genetic paternity obscures the full range of emotions and motives that influence nurturing tendencies in men, and may also obscure their impacts on child survival” (p. 159). Such strategic flexibility might explain the existence of otherwise puzzling cultural diversity concerning male sexual proprietariness, including so-called “partible-paternity” societies like the Eskimos, Montagnais-Naskapi, Central American people like the Siriono, and many tribes in Amazonian South America (p. 153).

Hrdy spends the rest of the book bringing more empirical data to the table and elaborating on the theory of alloparenting, including further analyzing the conditions that favor alloparenting in other species (chapter six), the features of babies that makes them so alluring (“sensory traps”) to adult caretakers (chapter seven), the importance of grandmothers in hunter-gatherer societies (“the most reliably beneficial of all alloparents” (p. 260)) and how this might have facilitated matrilocal (or “matri-patrilocal”) rather than strictly patrilocal residence patterns in the EEA (chapter eight), and finally,  a consideration of various life history traits such as long childhood and as well as some broad and speculative thoughts about how the rise of agrarian civilization affected female sexual autonomy (chapter nine).

To appreciate the significance of Hrdy’s scholarship, it helps to review a standard methodological procedure for doing evolutionary psychology. First, you identity an adaptive problem facing our ancestors in the EEA e.g. the problem of finding a good mate. Second, you develop a computational model that is capable of solving this problem e.g. gather evidence about proxies of fitness such as facial symmetry. Third, you hypothesize plausible neurological mechanisms that could realize the computational solution. Last, you run experimental tests looking for confirmation that the hypothesized mechanisms actually exist. Crucially, this methodology will only produce plausible results if you can realistically set up the initial adaptive problem. That is, if your assumptions about the problems encountered in the EEA are mistaken, then the rest of your explanation will inherit the mistake and you will end up proposing solutions to a problem that never existed. Accordingly, the success of evolutionary psychology as a discipline critically depends on using all of the scant evidence available to make realistic assumptions about the EEA.

Some standard assumptions about the EEA are unassailably right e.g. female pregnancy. But other standard assumptions about possible parenting investment strategies are more questionable. For example, I already mentioned the standard “sex contract” account whereby females “agree” to stop sleeping around with other men in order to secure their fatherly resources. This tense arrangement supposedly benefits both parties. The men receive assurance that they won’t waste resources on some other man’s baby, and the women receive assurance that they will have enough resources from a committed male to raise their baby. This story is supposed to take us all the way from the Pleistocene to contemporary cultural patterns of serial monogamy (albeit with occasional but limited cheating). However, several recent books  (Barash & Lipton, 2001; Ryan & Jethá, 2010)[3] have challenged the standard sex contract story on several dimensions (particularly the assumption that females actually are sexually monogamous). The most relevant dimension for our purposes is skepticism about the following assumption:  the strategy of a father providing care to anyone outside his direct kin network is not evolutionarily stable due to the pressure of competing “selfish” fathers who only provide care to their kin. In a critical review of the latter book, Ellsworth (2011) attempts to undermine the alternative narrative by approvingly citing Thornhill and Gangestad (2008) in claiming the “primary selective pressures favoring such female estrus adaptations were pair-bonding and dependence on male provisioning” (p. 332, emphasis added). However, if Hrdy’s emphasis on the importance of alloparental care for decreasing childhood mortality rates has any validity, then the standard sex contract story needs to be updated to allow for the possibility of more flexible and opportunistic female mating strategies. If alloparental care was available from non-fathers, then mothers would not have depended entirely on male provisioning and could have more room for strategic maneuvering through matrilineal coalitions and extra-pair mating  (Greiling & Buss, 2000).

While many details are needed to flesh out her narrative, Hrdy manages to synthesize a remarkably diverse catalogue of evidence from a variety of academic fields to paint a picture of the human species that tentatively answers the question: Why us and not them? The field of evolutionary psychology has long been accused of telling groundless “Just so stories” that miss the complexity of human life, but Hrdy’s book is a persuasive testament to the sweeping power of informed evolutionary explanation. Hrdy weaves decades of interdisciplinary research into a compelling and charmingly human story, one that challenges the necessity of overly Machiavellian or “demonic” metaphors[4] when describing the whole of our prosocial life, particularly when it comes to understanding the emotions that regulate the critical mother-child relationship. If nothing else, Mothers and Others paints a tantalizing portrait of what 21st evolutionary psychology might look like, and for that, Hrdy should be commended.


Barash, D., & Lipton, J. (2001). The Myth of Monogamy: Fidelity and Infidelity in Animals and People. New York: W.H. Freeman and Company.

Choi, J. K., & Bowles, S. (2007). The coevolution of parochial altruism and war. science, 318(5850), 636-640.

Ellsworth, R. (2011). The Human That Never Evolved. Evolutionary Psychology, 9(3), 325-355.

Greiling, H., & Buss, D. M. (2000). Women’s sexual strategies: The hidden dimension of extra-pair mating. Personality and Individual Differences, 28(5), 929-963.

Hawkes, K. (1991). Showing off: tests of an hypothesis about men’s foraging goals. Ethology and Sociobiology, 12(1), 29-54.

Herrmann, E., Call, J., Hernandez-Lloreda, M. V., Hare, B., & Tomasello, M. (2007). Humans Have Evolved Specialized Skills of Social Cognition: The Cultural Intelligence Hypothesis. Science, 317(5843), 1360-1366.

Hrdy, S. (2009). Mothers and Others: The Evolutionary Origins of Mutual Understanding. Cambridge, MA: Harvard University Press.

Ryan, C., & Jethá, C. (2010). Sex at dawn: The prehistoric origins of modern sexuality. New York: Harper.

Thornhill, R., & Gangestad, S. W. (2008). The evolutionary biology of human female sexuality. New York: Oxford University Press.

Tomasello, M. (1999). The Cultural Origins of Human Cognition. Cambridge, MA: Harvard University Press.

Wrangham, R., & Peterson, D. (1996). Demonic Males: Apes and the Origins of Human Violence. Boston: Houghton Mifflin.


[1] Hrdy claims that despite abundant evidence for intergroup conflict within the past 10-15,000 years, “there is no evidence of warfare in the Pleistocene” (p. 19). Rather, homicidal violence among hunter-gatherers “tend to involve individuals who know each other rather than warfare between adjacent groups” (ibid.).

[2] Hrdy also points out tha “cooperative breeding occurs in a taxonomically diverse array of anthropod, avian, and mammalian species, including some 9 percent of roughly 10,000 species of birds and at least 3 percent of all mammals” (p. 177).

[3] The latter book has a more aggressive and less scholarly tone than the former, but both are challenging similar elements of the standard monogamous sex-contract narrative.

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Review of Stuff: Compulsive Hoarding and the Meaning of Things by Randy Frost

Hoarding is a fascinating psychological malady where the compulsion to hoard things becomes so strong that it eventually starts interfering with the well-being of your life. Randy Frost’s recent book Stuff: Compulsive Hoarding and the Meaning of Things is a riveting look into the lives of hoarders and what drives them to manifest such seemingly irrational behavior. The book is chock full of curious anecdotes and interviews of hoarders that helps you get a sense of what it is like to be so absorbed in the life of things. Hoarding is interesting because we all remember traces of it in our own childhood collecting fads. When I was young I collected everything from soda tabs to pokemon cards. But it never became obsessive. That’s the difference with hoarders: they take a normal childhood tendency to collect things and go completely overboard to the point where they can no longer live safely in their own homes.

Frost goes into some detail outlining possible causes of hoarding and he finds that many hoarders suffered from some kind of emotional trauma early in life such as distant parents. He speculates that this lack of affection in people might have drove people to find comfort in the world of things. Hoarding also has a lot of commonalities with OCD. But the disease is complex and multifaceted and shouldn’t be reduced to just a few factors. There also might be interesting evolutionary reasons behind the hoarding instinct, but how deep into our history it goes is unknown since there are really no close analogues in animals such most animals hoard food not objects.

Hoarders are an interesting bunch. They are often highly intelligent with a good memory for details and a knack for telling stories about the histories of their objects. But their minds are so disorganized that they are unable to use their intelligence for much good. Their involvement in their things prevents them from leaving a normal life, and maintaining relationships becomes difficult when your homespace is completely unlivable. Hoarding places great burdens on children and spouses who have to live with it.

What I found really interesting about Frost’s account of hoarding is that it is very compatible with current research on the extended mind hypothesis. Hoarders often use their collection of stuff as an external memory source. They can remember the details of when they brought each object into their home. To throw away these objects would be tantamount to throwing away their own memories. Moreover, it is not just their memory that is externalized but their very personal identity. William James thought we all had a “material self” that bleeds into our personal possessions, but with hoarders this sense of self extends into ALL their objects, and not just special ones. They feel like their objects are part of their basic self-hood, to the point that it becomes emotionally traumatic to throw away a piece of useless trash. Hoarders often have deep personal histories with each of their objects, and what might look like junk to an outsider could be to the hoarder a treasure worth cherishing. Hoarders are also interesting because they seem to enjoy aesthetic qualities in everyday objects that normal people might only experience on psychedelic drugs. The stained pattern on an old milk carton might be beautiful to a hoarder and they just can’t imagine throwing it away.

What’s also interesting is the commonalities of objects collected by hoarders. One of the most common items is newspapers and magazines. Apparently many hoarders think of themselves as information junkies, to the point of saving every scrap of information they have ever come across. What’s interesting from an extended mind perspective is that these hoarders often don’t even read the newspapers or magazines. It’s just enough to possess that information, “just in case” they might need it in the future. They feel like just owning the information makes it “theirs” despite not reading it. In effect, these hoarders have externalized their knowledge into their collections of newspapers and they have accepted the externality of that information as a replacement for actually reading it. This kind of “just in case” mentality is extremely common in hoarding. Many hoarders see potential uses in objects than most people would simply discard. This “just in case” mentality leads many hoarders to buy multiples of items even if they don’t need it, like having 36 bottles of the same shampoo. They feel great anxiety if they are not prepared for the worst case scenario. But while some hoarders can’t throw away things because of a perceived potential, others can’t throw away things because they feel anxious by the thought of wasting something.

Hoarding is a complex and interesting affliction that effects millions of people around the world. Randy Frost’s book Stuff is an excellent introduction to the phenomenon that’s easy to read and filled with interesting stories and anecdotes. Frost also reports on the latest research designed to help hoarders with their problems. Unfortunately, hoarding is known as being extremely difficult to cure. Cities waste millions of dollars cleaning out the apartments of hoarders only to have them filled back up in a matter of months. By investigating into effective treatment programs, researchers will hopefully be able to help hoarders beyond the quick fix of heavy duty cleaning. All in all, I highly recommend Stuff.

Overall rating: 4.8/5 stars.


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Review of Daniel Everett's new book Language: The Cultural Tool

If you have been paying attention to the world of linguistics lately, then you will know that there is a paradigm shift in the works. The old paradigm is Chomsky and Universal Grammar, the idea that knowledge of grammar is more or less innate and not learned. The new paradigm is not quite a coherent movement, but it sometimes goes by names like constructivism, nurturism, machine learning, empiricism, and a host of other names. Basically, if you think that language is for the most part learned during childhood, then you are a constructivist. Dan Everett’s new book Language: The Cultural Tool is an excellent book defending the new paradigm and attacking the old. The Cultural Tool is above all a response to Chomskyans.

The Cultural Tool has a simple thesis: language is not innate, but rather, a cultural tool. He starts the book off with an anecdote about using a bow and arrow in the jungle. Obviously, the bow and arrow is a tool that was invented for the purpose of solving a problem. Although there are general cognitive dispositions that would have enabled humans to invent such a tool, it is very likely false that humans have innate bow and arrow construction knowledge. In the same way, Everett argues that humans do have some uniquely human cognitive dispositions than enable us to rapidly and efficiently learn language, but there is no such innate Universal Grammar that is the same in all humans.

The bow and arrow was invented to solve the problem of killing fast moving sources of protein. But what problem was language invented to solve? (“Invent” must also not be understood as necessarily reflectively conscious) Everett quite rightly argues that it was invented to help solve the problem of communication in a large group of primates. With language, communication takes on a new level of complexity in virtue of its abstraction and information carrying capacity. As Everett says, “Nouns and verbs are the basis of human civilization”. Moreover, Everett tells a nice, fairly plausible evolutionary story about how the needs of communication during a time of medium intensity environmental change during the final phases of the Pleistocene led to selection pressures for language. In a word, humans were in the right place at the right time with the right set of cognitive dispositions. Everett also gives a great defense of the idea that the “universality” of language learning can be accounted for without positing innate grammar by simply acknowledge the fact that all languages serve to solve similar communication problems, and thus have similar (but nonidentical) grammatical structures.

But Everett is also keen to point out linguistic diversity. And Everett is surely a renowned expert on this subject with his decades of experience working with Amazonian peoples. His work with the Pirahã is very well-known and he spends a good amount of time using the Pirahã as examples to support his thesis that language is a cultural tool. But I think a lot of people think Everett’s arguments depend on his interpretations of the Pirahã data. This is not true. The Pirahã are but one strand in his overall argument against Chomsky and Universal Grammar. If the Pirahã didn’t exist, Everett would still be capable of arguing against nativism. But his data on the Pirahã are very interesting and do, in my opinion, strongly support his basic thesis about constructivism.

My main complaint of the book is when Everett deals with the idea of there being thought without language. Everett thinks that nonlinguistic animals can clearly think. He uses the intelligence of his dog as an example. But obviously this depends on what we mean by “think”. If we defined it more narrowly as something like an introspective inner speech, think there is good reason to think “thinking” depends on language. This is actually more like “thinking about thinking”. But there is good philosophical reason to use the term “thought” to refer to such metacognition rather than the type of cognition shared by dogs and other animals. But so long as we are clear Everett is not talking about metacognition, it is really just a terminological quibble, for I surely agree with Everett that there is a good deal of cognition going on independently of learning a language. So Everett is not defending a strong form of the Sapir-Whorf hypothesis.

In summary, The Cultural Tool is an excellent book summarizing in an accessible manner what a response to Chomskyan theory could look like. It’s not a monumental work, so some of the details are left sketchy, but in general I get the sense that Everett is reporting on the development on a progressive research program. And if you are like me, then you will come away from the book with a better understanding of why Chomskyism and Universal Grammar is a degenerating research program. If you are a Chomskyan though, then you will probably be really irritated by Everett. That’s to be expected. But if you are at all skeptical of Universal Grammar though, then you will probably love The Cultural Tool. I think Everett has done the field a huge service by introducing a set of easy to understand metaphors to help us understand language. Thinking about language as culturally constructed cognitive tools as caused me to start thinking of all sorts of other things as tools, like philosophy and reason. So I think it’s an incredibly useful metaphor. Oh, but I do think Everett took the tool-idea a little far at the end of the book when he defended a strong philosophical pragmatism that consciously forgoes the quest for truth. Although in my younger years I would have loved this, Everett’s jump from linguistic pragmatism to philosophical pragmatism strikes me as a little naive. Of course we strive for truth! Or do you not think it is true that language is cultural tool? I would argue that the invention of the concept of truth was itself a great cognitive tool. But nevertheless, Everett’s book is well worth reading and I highly recommend it.

Overall rating: 4.8/5 stars


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