STEPHEN EMLEN: Let me welcome you all. My name is Stephen Emlen. And I'm a professor in neurobiology and behavior here. And I have the pleasure and honor of introducing you today to Dr. Sarah Hrdy from the University of California-Davis, who's here on her first visit as an Andrew D. White Professor at Large at Cornell.
For those who don't know about the A.D. White Professor-at-Large program, let me say a couple of things to put it in perspective. When the founding fathers of Cornell decided to let any student study any subject, and then they made the secondary decision of where to place this university, they were aware that Ithaca was kind of centrally isolated in upstate New York. And so at the beginning, they were concerned about having some way to make sure that top scholars, representing all the different disciplines, could come to Cornell not just to give a lecture, but to be available to students and all the scholars at Cornell, and also to the people downtown and the broader community.
And this would be possible by having the scholars come and stay for a week to 10 days, and not only that, but to come back on a repeat visit some years later to build on whatever happened the first time and therefore become more and part of the fabric, rather than just giving a lecture and running away. The conditions for the A.D. White Professorship, which really was formalized in 1965, were that groups of faculty could make nominations of prospective candidates who had the qualifications to be an A.D.White Professor at Large, which meant scholars at the top of their field, excellent communicators in any discipline, but best of all, that they're interdisciplinary. And Sarah Hrdy fits that to a T.
Sarah Hrdy basically was trained as an anthropologist. She started her career as a field primatologist, studying monkeys in the wild in India. She became very intimately trained in evolutionary biology, natural selection processes, and rose along with the whole sort of increase in interest in behavioral ecology and sociobiology.
She's been in the trenches in all of these areas. And as she got more involved, by taking a broad comparative perspective of primates, with a heavy emphasis on putting humans into the same frameworks, she has also become extremely knowledgeable about issues of child psychology, human development, and a great deal of the physiological processes that take place, especially in mothers as they become pregnant to give birth, bond with other individuals, manipulating, strategize to deal, as best they can, with the environment and other individuals, including males, who may or may not be paternal partners and so on. So her contributions are really wide and varied. I wanted to say that.
I see her primarily because of her communication of ideas and stimulating broad audiences among the scholars around the world through a trilogy of three books I'd briefly like to recommend. I'll mention them briefly in terms of the contributions that remain.
The first one is called The Woman That Never Evolved, which is a sort of tongue-in-cheek title, I believe. I don't know what she had in mind.
SARAH HRDY: I was going for the creationist audience.
STEPHEN EMLEN: [INAUDIBLE] creationist audience. This is was at a time when many behavioral ecologists were modeling and studying behaviors and interpreting them from a male perspective, chauvinist, if you want, in terms of how males can strategize in order to gain access to females, control access to females, even potentially monopolize females and the reproduction that females provide. And she wrote this book, which sort of undermines that in a very delightful, but very rigorous way and saying the females are not passive individuals in all this selection going on on males. But selection is operating strongly on female primates and female humans as well in terms of they, too, can make choices and manipulate situations in order to get the outcomes that are best from the female perspective.
Her second book that I like to put in the trilogy is called Mother Nature. And that says it all because the nature is she's bringing an evolutionary perspective or a lens to bear on motherhood, again using a comparative perspective across all primates, and heavily into the humans as well. She looks at the whole process, again, of female bonding, of females becoming pregnant, giving birth, lining up the right sort of coalitions or whatever the males might or might not help [? to ?] [? the ?] [? best ?] [? degree ?] possible, and goes quite a bit into physiological, as well as behavioral adaptations that female humans and other primates utilize.
I actually used the Mother Nature book for five years a row. And of course, I taught here about evolutionary perspectives on human social behavior. And it was a very good thing for students getting involved, getting excited, and then going off to the next whole series of things that that book sort of pointed the way to go to.
Most recently, 2009, I guess, she published another, which I consider the third of the trilogy, called Mothers and Others. And I won't say much about that, except that she has low expectations of only taking humans as cooperative readers as the underpinning of almost everything we think of in terms of empathy, understanding others, and the development and the theory of the mind as it applies to humans. So her task was moderate, but that's what she brought into this and we'll talk about today.
Before I really introduce her officially to give her talk, I want to say a couple of other things. An [? Andrew ?] [? White ?] Professor is here for a chunk of time. And Sarah is here really through this upcoming weekend. For those of you who haven't heard, who would like to get together with Sarah in some way to discuss things, we encourage you to contact the A.D. White Professor-at-Large program through its website or email and let us know, because there still are some slots [INAUDIBLE] where it's possible to arrange gatherings and get-togethers and want you to know that opportunity is there.
I also want to tell you that tomorrow she gives another talk downtown at noon, because the A.D. White Professorship is also to try and let this kind of scholarly work be available to people in the local community. She's giving an more-- [INAUDIBLE] describe this-- a talk that's aimed more at the people who are dealing with motherhood and family counseling and family dynamic therapy. Basically, it's co-hosted by Family and Children Services of Ithaca. And the title down there is Why is Male Paternal Care so Variable, why dads are so variable in what they do in the human species, a topic of interest, and also important to people on the ground, who are really working with families and mothers in need. And that's also open to the public.
And so it's at 12:00 noon at the Tompkins County Library in the [INAUDIBLE] Room, open to all tomorrow at noon, if you have the time and are so interested in that topic as well. And finally, I have to say that right after this, there's an open reception to which everyone's invited over at the [INAUDIBLE] Atrium, which is the next building over, just a stone's throw, the red brick building. Come on over, and Sarah will be there. So you can chat with her as well.
STEPHEN EMLEN: [INAUDIBLE], what did I say?
STEPHEN EMLEN: Course [INAUDIBLE]-- well, it's two departments. [? Anyway, ?] it's the red brick building, a stone's throw away. You're most welcome. So with that, I'm going to introduce Sarah, who's going to talk on this topic. She calls it The Origin of Emotionally Modern Humans, What it Means to Develop and Evolve as a Cooperatively Breeding Ape. I hope you'll join me in giving a Cornell welcome to Sarah Hrdy [INAUDIBLE].
SARAH HRDY: Well, let me just say it's a real pleasure to be at Cornell, a place with a school of Human Ecology. What a wonderful idea, the Brofenbrenner Life Course Center, and then the first neurobiology and behavioral department in the country, where so many of the faculty and students are doing this cutting-edge research on just what I'm most interested in, cooperative breeding, right now. So it's a great pleasure, and I really am grateful to Steve, to Meredith Small, Barbara [? Gusso ?] for making this possible, and also to Penny Nichols-Dietrich for helping me with niche construction after I got here.
And in return, what I'd like to do today is to try and integrate some of the strengths of this great university, talking about how what we're learning about child development, and also what we're learning about family life across animal spaces, can help us understand something that's really fairly unusual about the human species, which is our peculiar interest in helping others, in sharing others, even sharing food with others, which doesn't come naturally to most primates. And not only that, but we care what others think and feel. We care what they think about us. And we care what they intend towards us.
So like all apes, humans are very dominant striving, can be very competitive. And so you have to ask yourself, how on earth on, Darwin's earth, did traits that would make us so other-regarding evolve in an ape species? And why are such traits expressed so early in life, in infancy?
Well, the evolutionary study of infants can be said to have begun with the birth of Darwin's first son, William. And in Darwin's biographical sketch of William's development, he analyzed William's childhood fears by referring to the big animals who would have been roving around his ancestral environment. And sometime after that, John Bowlby, the great evolutionary psychiatrist, would refer to this as humankind's environment of evolutionary adaptedness.
And Bowlby proposed that in the Pleistocene environments, where humans evolved, in order to be safe, infants would need to be in continuous physical contact with their mothers, who became their secure base, and this was absolutely essential for babies to learn to regulate their internal states. Well, what grew into Bowlbian attachment theory is now really the foundation for much of the developmental research that goes on in psychology departments. And it led to a very welcome departure, at that time, from older dogmas about babies born blank slates.
And he revolutionized our understanding of infant needs. And I think, arguably, attachment theory is probably evolutionary thinking's biggest single contribution to human well-being. That said, there are some respects in which Bowlby's version needs to be expanded and revised today.
Like Darwin, Bowlby was convinced, correctly, that humans descended from extinct African apes, resembling today's gorillas and chimpanzees, a brilliant insight on Darwin's part. And so Bowlby looked to the primates, and he assumed a universal primate mode of infant care, where they'd be extremely possessive mothers who would be their infant's sole source of warmth, nutrition, locomotion, protection.
And this chimpanzee mother really exemplifies what he had in mind. She will not let this infant out of touch, skin-to-skin touch, for a single moment of the day or night for the first six months of life. And thereafter, she's going to go on staying close and suckling that baby for up to five years-- if it's an orangutan, up to eight years, extraordinarily long and close duration. But once that baby's weaned, it's going to provision itself.
Bowlby took as his templates for the environment of evolutionary adaptedness mother behavior in the Pleistocene. He took two species of great apes and two species of cercopithecine monkeys, so chimpanzees, gorillas, savanna baboons, and rhesus macaques. Well, as it happened, these are indeed all species where the mother remains in continuous contact with her baby. And he said, at the time, it was because all four of these species are adapted to a terrestrial existence.
But I think, also, he was influenced by stereotypes, very common in his day, dating back to Darwin, still common in our day, about the ancestral family structure and the idea that you have father, the hunter, who provisions; woman, the nurturer. In exchange for being provisioned, she provides him certainty of paternity with the sex contracts, [? first ?] to make sure he's not provisioning some other male's offspring. So I think Bowlby probably also unintentionally was influenced by very specific ideas about what a good mother should be doing, how mothers should behave.
Well, in this lecture, I want to explain, first of all, why I and some other evolutionary anthropologists are really starting to revise this conventional model to include care and provisioning by alloparents, by group members other than the genetic parents, in addition to parents. And this is, of course, cooperative breeding, any species where alloparents help parents to both care for and provision offspring. And I'm going to argue that there have been very unusual psychological byproducts of this in our species.
I'm going to begin, though, just by reviewing quickly the reasons for this paradigm shift away from the old model to a cooperative breeding model. Then I'm going to briefly summarize some of the demographic, life historical, and biogeographical implications of this, before turning to the cognitive and the emotional implications of this, especially for immatures developing in such a [? sense ?] system. Steve mentioned an earlier book, Mother Nature. In that book, I argued humans couldn't evolved with the life history traits we have, if they hadn't been cooperative breeders, and this has tremendous implications for maternal commitment, maternal love, and ambivalence, why maternal commitment in our species is so contingent.
I'm not going to talk about mothers today. And I'm not going to be talking about the most important male allomother group member other than the mother. That's the father. I'm not going to be talking about that particular allomother.
I'm going to be focusing on the implications for infants. And I'll be hypothesizing, by the end, that the peculiarly other-regarding impulses that I set out wanting to explain, which are very characteristic of humans, but not so well-developed in other apes, first emerged as byproducts of what for an ape was a very unusual mode of child rearing. In contrast to our closest great ape relations, human mothers are remarkably tolerant of others around them postpartum. And this is true for all of the societies still living by hunting and gathering when I first studied by anthropologists.
This is a [? Khoesan ?] Kalahari, sometimes called Bushmen, woman who's just given birth. And she returns to camp, and she gives her new baby to her own mother, who's massaging the baby's scalp. Wherever we have information on this, among Hadza hunter gatherers in Tanzania, baby likely to be surrounded by relatives held by allomothers 31% of the time. Mbuti, Central African foragers, new mother hands baby to a few of her closest friends and family to hold close to their bodies and so on.
As in all mammals, don't get me wrong about this, mothers are critically important. They're lactating. And they are a critically important attachment figure. This Efe baby will sleep with his mother. This is a primate universal. And she will remain the baby's main attachment figure.
But among the Efe, which are the extreme end of having a lot of allomaternal care, that baby will spend 60% of daytime being held by group members other than the mother, allomothers. So that can include the father. And here's the kicker. Infants with the most allomothers at age one are the most likely to be alive at age three.
And for the majority of societies, traditional societies, for which we have the relevant data, that is data on both family composition and child survival, having allomaternal caretakers is correlated with child survival. Well, if this is important, as I'm implying that it was, a couple of questions. First, who are these allomothers? Well, mostly they're kin. Father, brother, cousins are the male allomothers.
Among the female allomothers, sisters, aunts, and grandmothers, but non-kin also can be involved. There's a lot of as-if kin that live in these groups and join and leave and join and leave. So it's not entirely kin.
Second question, if it's as important as I've been telling you, why didn't we know something about this before? How are we just coming to this now? Well, in the developed world, 98% of those born are going to survive to maturity. And most of our studies of child care and child development were conducted among such people.
In traditional societies, where you don't have walled houses or predator control, vaccinations, clean water, pasteurized milk, mortality rates 40% to 80%, under some circumstances higher, are what's common. And this is also true for many wild primate populations. [? It ?] was almost certainly true for our Pleistocene ancestors.
So babies in the genus Homo are about the most expensive of all mammalton. They're larger at birth. They're 6% of the mother's body mass at birth, compared to 3% in other apes. And this is probably something that goes way back.
Jeremy da Silva has hypothesized that you're already starting to get big babies with Australopithecenes and much bigger babies by Homo erectus. They're very costly to rear. They remain nutritionally dependent longer than any other primate. It takes 10 to 13 million calories beyond what the child can produce or provide or gather for himself to rear a human forager from birth to about age 18.
This is just so much more than a foraging mother could provide and still stay alive herself. Yet infants are weaned earlier than in other apes. And mom is going to give birth again after shorter intervals than other apes, before the older children that she already has are independent.
And for those of you trained in behavioral ecology and know something about trade-offs, you're probably saying, but how can this be? Worse, hunting is a very, very dicey way to get food in humans, very low success rates for hunters and scavengers. They can go off days and days in a row and come home empty handed.
So as apes included more meat in their diet, paleontologists and behavioral ecologists, like James O'Connell and Kristen Hawkes have stressed that, look, you had to have had more than one hunter. There's a lot more solitary hunting out there than you might think. More than one hunter out there bringing back. And when hunters are successful, they're having to pull and redistribute it with the minimal daily caloric intake.
Remember, kids have to eat several times a day to stay alive, minimal daily caloric intake insured by a division of labor, between hunters providing high-value, much-desired protein and fat, and an array of gatherers returning to a central place. These data are from Frank Marlowe's wonderful new monograph, [? "Hadza ?] Hunter [? Gatherers." ?] I have to tell you the graph would look exactly the same for the [? !Kung, ?] Richard Lee's classic early work.
60% of the calories in there are plant foods gathered by women. The meat is about-- meat and honey about 40% of the diet. And Frank stresses that, yes, men often will try to channel food to their own offspring, meat to their own offspring.
But there's such a strong ethic of not appearing stingy. They're very concerned with reputation. So meat is virtually always shared. This is very characteristic of hunter gatherers. And in other words, meat is being provided to the group by individuals who aren't necessarily the fathers of those receiving it or the mates.
And what's interesting about the female thing-- I don't seem to have a pointer. But just look over. It's the 40- to [? 50-, ?] 55-year-old women who are actually the hardest working. These are the women that Kristen Hawkes, back in 1989, called the hardworking Hadza grandmothers. They're not necessarily grandmothers.
This woman in the picture from Hawkes and O'Connell is a 62-year-old great aunt. And she's working really hard to move that boulder to get at underground storage [INAUDIBLE]. Thank you. How does it work. Let's see. Oh, and the-- thank you. It takes the male touch. Never mind.
Women with very young children actually are bringing in much less food, even though they have young children back at camp. So to compensate for shortfalls, you have to have alloparents in addition to parents. And that's the main reason for the paradigm shift.
In order for this to work, though, you have to have flexible residence patterns. These are very mobile people. Over their lifetimes, individuals move multiple times, gravitating away from adversity towards opportunities, where the opportunities are not only access to better food and water, but also access to individuals who are going to help care for and provision your children and also perhaps opportunities to give care to kin who most need it. So that for example, a grandmother who happens to be still alive, which isn't always guaranteed, when her daughters are giving birth, and she has several daughters, one of them has a husband who's just died. That's the one she's going to go live with and help.
A young man typically comes to live with a young woman's family, hunting on their behalf for several years until after one or more children have been born. So she's around matrilineal kin at the first birth, very risky time. Thereafter, they may stay. They may move back to his people, to a patrilocal residence. Or they move to some group altogether.
So Frank Marlowe likes to call this pattern multilocal, and I've adopted it. I think it's very good, that children grow up not even thinking in terms of a patrilocal residence. And this is important. Because if you have textbooks on this, you may very well have read that humans are innately patrilocal. That's really incorrect.
So why would anybody ever want to raise anybody's children other than their own? I don't think I need to go into this in this. I'm in cooperative breeding central here at Cornell. Those of you who've taken any of Paul Sherman or Steve Emlen's course know all about Hamilton's Rule, that helping evolves when the cost to the alloparent is lower than the benefit to the infant times the degree of relatedness.
I'm going to try again. Well. So what this means is that kinship can often play a big role. So for example, in [? Davies's ?] [? dunnocks, ?] you have males bringing in food roughly in proportion to how often they had chances to breed with that female when her eggs were fertilized. Meerkats, you have helpers only helping when they're in good condition. They don't really need it themselves so much. So they help when they can.
And over time, as this becomes a fitness benefit, helping like this, the criteria or the threshold for responding to cues of need from infants get lower and lower over generations. So that, for example, you can sometimes have these mistakes, as in the case of this bird, this-- what is that one? She is a--
STEPHEN EMLEN: Cardinal.
SARAH HRDY: It's a cardinal, exactly. This cardinal. Who's stuffing food into the gaping mouth of a goldfish, and that's misdirected parental care. Highly social species with helpless and altricial young are really susceptible to the enticing cues of these babies.
This is my neighbor's Jack Russell Terrier, who chased away a very surprised mother cat, proceeded to spontaneously lactate and suckle her kittens. And of course, she descends from a long line of cooperatively breeding wolves. So maybe we shouldn't be surprised, but these kittens are going to grow up a little bit confused.
And this is a Cebus monkey who happens to find an abandoned baby marmoset in the woods. She's lost her own baby, and she adopts it. And she rears it. Well, our species also is very, very susceptible to babies. It's a point that's not lost on Madison Avenue.
Those of you who may have seen Thomas Balmes' blockbuster film recently, Babies-- what I love to do-- I love the film. But what I really liked was going in and sitting in the audience and then turning around and watching the audience watching everybody else's babies. And they go, gaga. And no wonder.
Kringelbach at Oxford and others have shown that when you look into the face of a baby, the reward centers and your brain fire. And the press goes crazy and says, oh, the source of parental instincts. The problem is, in Kringelbach's study anyway, half the people in the sample were males, half were females, and half were parents and half were not parents. We are very attracted to babies as a species.
Just briefly, there are many different evolutionary routes to alloparental care. They vary. But the point is it's evolved many times among social insects in 9% of 10,000 species of birds and maybe-- this is not a good figure-- 3% of 5,400 species of mammals. But it's especially likely to evolve in social carnivores, like these Indian dholes or this wild dog. This is a male helper, who's eaten some food, and he's regurgitating baby formula into the mouth of this pup that was waiting back at the den.
And it's especially likely to evolve in social carnivores and, we're just finding out, also in primates. Allomaternal infant care-- that's just part of the cooperative breeding story-- characterizes over half of the species in the primate order. And I have to tell you that for any of you who've read Mothers and Others, I actually consciously erred on the conservative side in everything I said there because it was so-- I thought, no one is going to believe this.
I'm now convinced that shared care is even more common than I said there. And some subfamily, for example, the subfamily Colobine, these are the [? langur ?] monkeys that I used to study. Almost all of them have infant sharing, others, cercopithecine monkeys, only a few, [? the ?] Old World monkeys.
So what's interesting, though, is how you have gotten such-- it's so important for the mothers who are going to breed faster, with all this help caring for their babies, that there has been runaway social selection on babies to develop these very flamboyant and attractive cues. This is not for their mother. This is a cue to allomothers, come get me.
Allomaternal care and at least minimal provisioning is more rare, but at least minimal provisioning is present in maybe 20% to 25% of all the species in the order primates. Maternal provisioning, though, ranges across the map, from two females who are both mothers co-suckling in a nest, [? Galagos ?] [? Microcebus. ?] In captivity, it's primarily the grandmother who is the co-mother.
Cebus monkeys, females other than the mother will allow babies to take food. But then they also will allow someone else's baby to have a brief little pick me up and have some milk. But it's nothing major. Major provisioning in these guys, the Aotus night monkeys and Callicebus, the titi monkeys, but they're unusual among primates because they're strictly, strictly monogamous.
Primates tend to be very polyandrous and mate with more than one male. But these guys, the male does such a good job of mate guarding that really it doesn't happen. They spend their time with their tails twined together. It's very sweet. And this is the only species, these titi monkeys, the only species I've ever heard of where the baby is actually more attached to the father than to the mother. And the male carries the baby all the time, except when the mother's suckling it and at night, and also around the time of weaning does some heavy duty provisioning, as well as heavy duty lifting.
But extensive alloparental-- this is definitely parental care. Extensive alloparental care plus provisioning, you only find in a group of Old World monkeys, the Callitrichidae, 35 species of them, marmosets and tamarins, and in humans. My point, though, is that traits conducive to the evolution of shared care are very widespread and highly conserved in the order primates.
What it takes is the right conditions for these to be expressed and then selected for. OK, but what are these conditions? Well, first and foremost, the mother has to think it's safe to turn her very vulnerable newborn over and allow somebody access to it. And that's where the residence pattern comes in. I'll be talking much more about this on Friday than I have time to talk about today.
OK, what else? Well, they have to be highly social. There have to be benefits to being in a group. You tend to have-- this is based on comparative evidence across species, such as a lot of the work being done here at Cornell-- unusually large altricial babies dependent for a long time. And of course, if you have individuals bringing food back to a central place, this puts them in the right place to be exposed to those enticing cues.
Carel van Schaik and Maria [? Noordwijk ?] and others in the Zurich group have stressed the importance of this combined hunting extractive foraging. Marmosets and tamarins are basically hunter extractive forager/gatherers. I think meerkats would actually fit into this. Cebus monkeys would fit a bit and humans, for sure.
And then, very importantly, and this actually comes out of Steve's early-- his 1982 paper where he wasn't just talking about saturated habitats, but also unpredictable climates. And Dustin Rubinstein, from here, has recently done a lovely paper together with Walter Jetz on the correlation in birds between living in a place with very unpredictable rainfall and unpredictable resources and the evolution of cooperative breeding. Well, that just fits so nicely with work being done in the early Pleistocene, early hominids, work by people like Rick Potts, who are absolutely convinced that eco instability was the great push in a lot of human evolution.
This is one of several dozen similar pictures I could show you from Potts's work. But this is just an early hominid site at Lake Olorgesaile just showing you that between 1 million and 600 years ago, the lake level goes from deep to shallow to deep to shallow. And then today, I'm sure you've seen it on Nova and things, it's just a desert, very unpredictable resources.
So with young buffered from starvation, some groups are able to persist, even under very harsh conditions. And when things improve, they can colonize new habitats. We know this about Homo erectus, an incredibly colonizing species. And when conditions improve, then they can expand, which, for better or for worse, humans ended up eventually really doing.
Hominid youngsters could also take longer to grow up. And a very interesting body of work, some of it presented at meetings, some of it still not entirely published by Karin Isler and Carel van Schaik at Zurich, where a lot of wonderful work on co-operative breeding is being done, have shown for 540 species of mammals that if you separate out the mammals that are very altricial at birth, where most of the brain growth is during that provisioning period after birth, then you get a very nice correlation between brain size and co-operative breeding. But otherwise you don't.
Marmosets, for example, you don't. But then they actually have brains fairly mature already by birth. So that explains why they don't fit. Anyway, I'm really eager to see how this work is going to go down because it's very, very tantalizing.
So much for the demographic and the life historical [? implications. ?] There are also going to be cognitive and emotional implications for mothers, for allomothers, and especially for immatures, who have to grow up dependent on not only contingent investment from mothers-- because remember mothers in cooperative breeding species, their commitment is a little more contingent because it depends on how much social support they perceive they have. They have to not only monitor and worry about their mothers, they have to worry about all these others as well.
So here's where I'm going. The line of bipedal apes leading to anatomically and behaviorally modern Homo sapiens splits off from the other apes. This, the chimps and line leading to humans, split off from orangutans about 15 million years ago. The line leading to the genus Pan splits off maybe seven, eight million years ago.
And one of the guys I'm most focused on here is Homo erectus, this very wide-spread, very polytypic, very variable, sometimes tall, sometimes short, brains about 900 cubic centimeters, so not quite human-- 1,350 cubic centimeters-- but certainly much bigger brains than you have with Australopithecenes or chimps, just 400 CTs. They start to emerge about 1.8 million years ago.
And what I'm going to tell you now is about work comparing human children with orangutans and chimpanzees. And when Mike Tomasello's group, at the Max Planck Institute for Evolutionary Anthropology in Leipzig, took 105 two-year-old children, 106 chimpanzees of all ages, and 32 orangutans, and they ran them with a specially designed battery of sociocognitive tests, what they found is that in terms of spatial aptitudes, they fall really in about the same range; in terms of quantitative abilities, assessing many versus few, about the same range; in terms of causality-- what happens if you push something with a stick? It falls over-- about the same range. They're about equally good physicists there.
But the big differences were down in this social realm, social learning, watching a demonstrator solve a task and then having to solve it the same way, humans much better. In terms of communication, what am I pointing at, where's the treat hidden, humans better. In terms of what psychologists call theory of mind, being able to understand that somebody knows something that you don't know, that they have a mental state separate from yours, again, humans better.
But be sure, and you notice that it's not that other apes can't do these things. It's that humans are just so much better at it. Other apes do have a rudimentary theory of mind. They know what the dominant animal can see and not see. That's why they hide certain things.
In addition, humans, right from a very early age, are more eager to share, and they do it spontaneously and voluntarily. And they'll even do something like pick out something that they know someone else would especially enjoy. This is something you don't see in other apes. And as young as two, and some like Vasudevi Reddy would argue even much earlier, they care. They have a sense of pride and shame. They care what someone else is thinking about them very early on that.
Now, look, other apes do sometimes share food. This is a study, a John Mitani study. The dominant male has just killed a baby Colobus monkey. One of his very important strategic allies wants some. He's reaching up. He's actually going to give him a little bit.
This is a bonobo female. Female bonobos will allow another female's infant to remove food from their mouths. But importantly, they have to be begged first. And it often looks more like tolerated theft, scrounging. It's not a kind of considered gift giving that anthropologists have documented for every human society ever studied.
When you combine intention reading with other tendencies-- you care what someone else is thinking or feeling or what they want-- then you can coordinate behavior to achieve a common goal in a way that other apes apparently have never managed. These are Kayapo tribesmen. They're beating this timbo plant that's going to release a toxin. And then women and children are going to walk around in the shallow water, gathering up this tremendously rich protein source that just would not be available even with Stone Age technology.
Other apes often had various kinds of stone tools and things that they're using. So they have roughly Stone Age technology. They don't have this.
Well, back in 1977, when Andrew Meltzoff first discovered that newborns can imitate the facial expressions of their caretakers-- if you don't believe this, try it in an airport sometime. Just go find yourself a baby and make faces. And if you get them in the right mood, they do it. It's remarkable.
Anyway, it was assumed that this was a uniquely human neurocognitive response. And it was part of our machinery for developing empathy and theory of mind. The problem, of course, is that we now know that newborn chimps have it as well. They have mirror neurons, after all. And they can scan the faces of their caretakers, imitate, and so forth. The basic wiring is there.
But what's interesting-- this is the work of Tomonaga-- is that after some months, while little humans are getting better and better at this, so that by nine months, if I hand this gadget that I can't master to-- [? I'll ?] [? be ?] [? a ?] [? baby, ?] and I hand it out to someone else, and the baby's watching. The baby wants to know what does that person think about this, this sort of triadic interaction, where the object, baby, caretaker, what does the other person think? Little chimps almost never do that.
So what could be responsible for this strange emergence of other-regarding traits in the human species? I don't have time to go over all the explanations that have been offered. But far and away the most widely cited one is this one, the lethal inter-group conflict hypothesis, Sam Bowles, his famous quote, "do we engage in mutual aid because evolution is red in tooth and claw?" Conflict is altruism's midwife. Generosity and solidarity towards one's own may have emerged only in combination with hostility towards outsiders.
Well, I think Bowles and those guys are exactly right, that having an out-group competitor, having to worry about being wiped out by the neighboring group or wanting to take over their resources, has been very important in shaping the humans that are around the planet today, no argument with that. But I don't think we know that, in fact, these conditions go back 1.8 million years ago to the early emergence of Homo erectus and also 200,000 years ago to the emergence of early humans. So I don't have time to go through this in any detail.
But basically, even if humans and chimps did share a common heritage of inter-group warfare, because chimpanzees but not bonobos do have inter-group hostility and try to kill off other groups, even if they had increasingly sophisticated capacities to identify with and attribute intentions, if you could get that just by passing through a crucible of inter-community conflict, and if, as we have recently learned, other apes have the cognitive underpinnings that allows them to learn from and imitate and empathize with others, well, then we would still have to explain well, why, arguably, even more violence-prone ancestors of chimpanzees didn't spend the last seven million years evolving to be more other-regarding as well? So this is why I think it's very important to maintain an open mind and to take into account alternative proposals. And I worry that by focusing so exclusively on warfare, something that may or may not have been going on among our Pleistocene ancestors, we're overlooking conditions, such as the very un-ape way our ancestors were reared that are just as important and, of course, in my opinion, more important for explaining the initial-- the initial emergence of other-regarding tendencies.
none of us has a machine to go back and observe how early hominid children were responding to multiple caretakers. But we have some wonderful proxies. What we have or children [? today. ?] And what psychologists tell us, for example, is that a baby that is off his or her mother, being held by someone else or on a couch, spends more time looking at faces, monitoring eye gaze and expressions than when they're in physical contact with their mother.
Well, historians of the family and social psychologists have known, social workers, too, have known for a very long time that living in an extended family has very important repercussions for child development, maternal attachment, and other things. For example, the presence of a maternal grandmother in a household, especially a household with a high-risk mother, you have increased maternal sensitivity to infant needs. The mother, with this other woman there as a support, is more sensitive to her child, more responsive, more secure infant-to-mother attachment. It actually has an effect on how secure the infant feels and how attached he or she comes to his mother. [? Enhanced ?] cognitive abilities by age four.
The presence of older siblings in the household-- you get a more sophisticated theory of mind by age three, improved social skills at older ages. And these guys, Ruffman and Permer, when they first did this study, they quipped. They said, theory of mind, it's contagious. You catch it from your older siblings. And then they redid the studies and it turns out just any kind of older caretakers.
And then really importantly, Marinus van IJzendoorn and Abraham Sagi looking at Dutch and Israeli children-- enhanced capacities to integrate multiple perspectives in children with multiple caretakers. Well, this is very interesting. Recent work at Yale, Kiley [? Hamlin, ?] Paul Bloom and their associates, the impulse is to monitor others and assess their intentions. And these lay the groundwork for being able to do things that are important later on, like assigning reputations to others, who is helpful, who is not.
These start very early. These are children as young as three months old. This is long before language, months before language. They show them cartoons. There is this little red ball trying to get up a hill, and this is the nice yellow triangle. It's going to help him.
And over here, the little red ball is trying to get up the hill, but this nasty blue square is pushing it down. And then afterwards, they see which cartoon figure does the baby spend longer looking at. Which one does it reach out to? Which one does it prefer?
And it's the yellow triangle. So already, at that very early age, they're assessing these qualities. Well, let's look now across species. Let's look across at some other primates.
Independent experiments by Judith Burkart at Zurich, experiments at Harvard and Wisconsin, with cooperatively breeding marmosets and tamarins, these experiments were deliberately designed to test, in the same way that Joan Silk and her colleagues had tested with chimpanzees in that famous article in Nature about chimpanzees being indifferent to the well-being of others, because they don't do this. This little guy isn't going to get this mealworm.
But there it is, pulling, and he's going to get it, very other-regarding, they called it. So far as mutual tolerance and other-regarding impulses go, it appears that being a cooperative breeder is a lot more important than having a big brain. These guys have brains smaller than walnuts. And they are surprisingly altruistic in the wild as well.
So for example, Paul Garber reports for wild tamarins that you have 52 cooperative interactions for every aggressive interaction, which is very un-primate like. Just a quick summary of tamarins and marmosets, and I'm actually lumping together a number of species because there are important differences between some of them, but typically the mother only gives birth to twins or triplets. Dad carries them around all the time, except there's more than one dad because they have these chimeric young that can have more than one father in the same individual.
And furthermore, mothers are mating multiply. But even males who aren't related, males who may have entered from outside it are actually collecting food. They're hunting and gathering. And they are providing it to the babies. They have collaborative foraging, in the sense that they'll work together to open a hard-to-open fruit to get at the kernels inside.
So I've been emphasizing, in the last minute or two, all these helpful acts. Just remember that they also are very competitive. So typically, there's just one female breeding. And the alpha female, if she's pregnant, and some other female in the group gives birth, she will kill the infants because she doesn't want to have to share the baby sitters. And she'll do so even if she's the mother of the mother. That is this is the grandmother from hell.
And so it's not all hunky dory. But there's an amazing amount of cooperation among marmosets and tamarins. So here's where I'm going with this. I'm going to ask you to join me in a thought experiment.
I want you to take a highly intelligent bipedal primate with a cognitive and the manipulative potentials that we know that all the great apes have and we can assume our common ancestor had, has rudimentary empathy, rudimentary theory of mind. Frans de Waal makes this point all the time, which is don't get carried away. Chimpanzees can be empathetic. And it's true. They do sometimes help others.
Then you rear that ape in a novel developmental context, where maternal care is contingent. And the infant depends on care and provisioning from multiple others, has to monitor the mothers, respond to her, rev up, rev down, depending on her, but also find out who is it we're soliciting from? Who's going to be helpful? Who do you kind of not want to catch the attention of?
And then subject-- at the end of the developmental process, you're going to get a very novel ape phenotype. You're going to get a little ape that actually is a little bit more like some of the apes that are reared by humans, that have multiple allomothers around. And they're much better at responding to pointing. They're much better at giving you things when you ask and so forth.
You're going to get a different phenotype. It's not going to be human. But it's going to be a different phenotype. Then subject this novel ape phenotype to very novel selection pressures, because for the first time, the little infant apes who are best at mind reading and the best at understanding the intentions of others are going to be the best cared for and the best fed. Well, what do you get?
In high child mortality environments, you get directional selection favoring just the traits enhanced mutual tolerance, social learning, social communication, perspective taking, that comparisons between humans and other apes are requiring us to explain. So this is why I've argued that long before what's called behaviorally modern humans, that is with symbolic thought and brains capable of language, in the last 100,000, maybe, years, and before the evolution of anatomically modern humans, that's at least by 200,000 years ago, what I'm calling emotionally modern humans, other-regarding and actually questing for inter-subjective engagement with other individuals, were already beginning to emerge.
Steve said that I'm trying to explain everything. Actually I'm not. What I see this as is I'm trying to explain the underpinnings for what comes later. I'm thinking that our ancestors were already very, very different from chimpanzees, and that this is really the prequel to the major human developments later on.
So it's really symbolic thought, language, cumulative culture, social norms, social selection for well-intentioned partners [? that ?] [? could ?] lead to morality, that's far in the distance. These emotionally modern apes are just explaining this one thing, the emergence of other-regarding impulses and answering one question, why in us and not in them? Thank you.
[? STEPHEN EMLEN: ?] [INAUDIBLE] questions? Raise hand and speak loudly.
SARAH HRDY: Yeah?
AUDIENCE: Is there evidence is other-regarding [INAUDIBLE] other-regarding grandmothers?
SARAH HRDY: No. No. It's not something anyone who studies infant development and child development and life course-- no one has even thought of doing that. What we do know, though-- can we-- well, maybe not.
What we do know is that children who are securely attached and feel secure about their world and who have been nurtured by responsive caretakers grow up to be responsive caretakers. That's pretty well documented. So it's consistent with what you just said.
But even talking about other-regarding impulses in apes and in human evolution, it hasn't been talked about. So nobody's looked. And until somebody sticks their neck out, no one's going to look. Someone is going to do it, just if only to prove me wrong, which is fine. But it hasn't been done. Yes? Yes?
AUDIENCE: That was a marvelous talk and to an outsider, a revelation to all sorts of [INAUDIBLE]. It struck me, however, as being a bit Whiggish, that everything was getting better.
SARAH HRDY: British?
SARAH HRDY: Whiggish, optimistic?
AUDIENCE: Optimistic, [INAUDIBLE] yeah. You didn't talk about competition--
SARAH HRDY: No.
AUDIENCE: --within groups.
SARAH HRDY: No.
AUDIENCE: For example, my wife is only 5-foot tall. And she swears that [INAUDIBLE] elder brothers, [? who are ?] [? 5' 6." ?] It certainly wasn't [INAUDIBLE] [? a ?] constructive [? element ?] [INAUDIBLE].
SARAH HRDY: Absolutely.
AUDIENCE: There must be the back side [? of this ?] and reading [? people's ?] [? end ?] [? means ?] [INAUDIBLE] individual [INAUDIBLE]. Do the studies [? not ?] talk about this? Or is it just that they're not very well [INAUDIBLE]?
SARAH HRDY: I'm just so glad you asked that, because, of course, it's a very important question in there. I want to answer it at several levels. First of all, the older brothers probably did impact your wife's growth and probably her IQ as well. There's where the data are, that older siblings, firstborns, have all these advantages in our Western society.
In hunter gatherers, actually the data are the other way, having older siblings is actually better for you. So Frank Sulloway's wonderful book, Born to Rebel, about birth order and sibling competition, I love his book. It's wonderful in terms of explaining, for example, [? scientists ?] [? and ?] French [? revolutionary ?] because those are all Western cultures. It wouldn't
Work for hunter gatherers, where having older siblings is a net plus, usually, because they help to rear you and to provision you. But yes, you're absolutely right. Competition is a big story in every aspect of nature, right?
And one reason I can get away with this, in a way, with my colleagues, without having my evolutionary credentials stripped, is because so much of my early work was on competition and male-male competition and infanticide and stuff so that my colleagues at least know that I am aware of competition. That said, you mentioned, [? though, ?] has this just not been studied? As it turns out, hunter gatherer societies, the adjective that is usually applied to them is fiercely egalitarian, sharing, communal.
And it's appropriate in the sense that, to a degree that Westerners can barely understand, these people do share. But there is a background to it. And one of the sources of this is that those who are stingy, those who don't share, people vote with their feet. They just leave. And he wakes up one day, and everybody's gone.
Or if he's a bully, they may gang up on him. And they may get his relatives to actually do the deed so there won't be a lot of recriminations later on. There are sanctions against people who don't share, but they're very subtle. You're not going to see them.
So you say, have they been studied? No, they haven't been studied properly. And so for example, I was in the last stages of writing Mothers and Others, and I was worrying about exactly this thing. I mean, all the reports were about sharing and giving.
So I called up Paula Ivey Henry who did this classic, classic work on the Efe and infant sharing. And I said, isn't there any competition? And she said, well, you know, I wondered the same thing. And it turns out that the women who get to certain gathering places sooner, send up their children to get food more, and there is competition for this. But it's very subdued, for the reasons that I gave you.
And they're very dependent on others. If you don't have people to share with you, you're going to be in bad shape, not just people in your own group, but people in neighboring groups and these wonderful exchange systems that Polly Wiessner and others have done such a beautiful job of documenting. It's an enormous part of their lives. And now because of some work that Steve's doing, I'm thinking much more about-- I'm talking about the movement between the groups and those permeable boundaries.
They're probably not as permeable as the literature suggests. And I asked Polly Wiessner about this recently. And she sent me the most wonderful-- well, I better [? not show it-- ?] wonderful photograph of two Bushman men talking and assessing what's going on in your group. They're no longer living as hunter gatherers, by the way. They're in settlements.
But they'll talk among themselves first to say, is it a good idea to move here? It's very subtle and very tactful, and nobody's pushy. And they sort of wait. And if you're kin, there's a different set of criteria for coming in. So yes, but it's all below the surface.
Has anyone here seen the movie The Fast Runner? Yeah, and that's like Eskimo film. It's the first feature-length documentary in Inuit language. The film just makes you weep how hard these people are trying to avoid confrontation and conflict, in spite of being primates with sexual jealousy, competition for mates, envy.
These things don't go away just because you're living like this. But they have stratagems and I would argue also emotional adaptations to try to reduce some of these tensions. So yes, there's competition, but it's very subdued compared to what we in Britain and the US take for granted.
Yes, you're right. It hasn't been well studied. Ethnographers-- it hasn't been in the picture. I think it will be better studied. But unfortunately, the cows are out of the barn. It's a bit late. [INAUDIBLE], I mean, competition is a very important part of this. But it plays out differently in these hunters and gatherers than what you're thinking.
And you know I'm reminded of the accounts of when Christopher Columbus comes to the New World, and the Arawak Indians come out to meet him. What they are is they're desperate to establish trading relations, some kind of exchange relations with this guy. And they're bringing out all these gifts and not expecting, immediately anyway, as far as Christopher Columbus and his crew can make out, anything in return.
Christopher Columbus writes in his diary, these people are so simple. With just 100 men, we could make them into slaves. He's thinking, how can I turn these people into a commodity? And they're thinking, how can I turn these people into future trading partners and exchange partners and people to share with, just a totally different mindset. Does that--
AUDIENCE: I'll ask one more quick one. You say you can't go back with a machine 200,000 years to see what's really going on at the beginning of the Pleistocene.
SARAH HRDY: In terms of children's responses.
AUDIENCE: [? Yeah, ?] exactly, in terms of--
SARAH HRDY: It doesn't fossilize well at all.
AUDIENCE: What kinds of things can you see that will allow more supportive evidence or rejection of your ideas since we can't go back? Are there [INAUDIBLE]?
SARAH HRDY: Yeah. I'm hoping it's coming very soon. One of the things we need to know is in chimpanzees, for example, we know that in humans there are these orbital frontal cortices lighting up when people see babies and its reward centers. We know that prolactin goes up when males are in intimate contact with infants, and testosterone goes down.
Are these responses anything like so pronounced in chimpanzees, which I'm arguing evolve from species that didn't have cooperative breeding? So I would expect to see those neurological and endocrinological cues. It's going to be very difficult, for a lot of reasons. One, there are such excellent ethical reasons for not doing things like this to chimpanzees, not always appreciated.
But there are people like Tetsuro Matsuzawa, in Japan, who managed to get their data in the most humane way you can imagine. It takes them longer, and it costs them more, but it is humane. There's that problem. There's also the comparison problem.
So you're going to say, well, what would be more of a prolactin response in a chimp compared to-- I don't know. So I don't think it's going to be easy. But that's testable.
Other things that are testable is-- one of the arguments is, is that we evolved long childhoods because we needed to learn all these important things. But if it turns out, if the fossil evidence shows that childhoods are getting longer before we have 1,350 CCs of brain, well, this is interesting. It suggests that we were doing something else, like co-operative breeding, before the big brains evolved.
So there's ways you can get at it. But I don't think it'll be certain. And I don't think it'll be easy. And I expect we're going to have a lot of wrong turns.
AUDIENCE: It shows the necessity of this interdisciplinary way of looking in order to find ways of [INAUDIBLE] information [INAUDIBLE].
SARAH HRDY: Right. I think it's already beginning to change the work on allomaternal care and infants in comparative psychology and I hope in human developmental psychology. The people studying voles are no longer-- they're talking about alloparents all the time now and babies responding to [? alloparenting. ?] It has already come in there first, and it's partly through [? Sue ?] [? Carter, ?] and [? Sue ?] [? Carter, ?] who has egged me on in a lot of this work.
So yeah, it's already starting to happen. Of course, it's going to spill over into the human work. And I still get in trouble sometime with people who think that I'm criticizing Bowlby, and I don't think mothers are important, and this. And because so many of the paradigms in attachment theory, it's built on mother leaves the room, that no one really looks at so what happens if the baby is very much attached to the grandmother? Can she substitute and stuff? We really don't know.
And all these data that show children are better off if in a two-partner family than in a single-mother family, well, duh, because it's just so hard to rear children. But they haven't looked. Are they actually any worse off if it's an extended family with various relatives, not necessarily the mother and the father? We don't know. But I think that will change.
STEPHEN EMLEN: Well, I want to invite everybody to go over the [INAUDIBLE] for a reception, if you'd like and join me in thanking Sarah Hrdy.
We've received your request
You will be notified by email when the transcript and captions are available. The process may take up to 5 business days. Please contact firstname.lastname@example.org if you have any questions about this request.
Sarah Hrdy, professor emerita of anthropology at the University of California-Davis, a renowned anthropologist, primatologist and human behaviorist, spoke at Cornell on October 17, 2011 during her first visit to campus as an A.D. White professor.