You can never have too many mothers

Babies are what bring us together, according to sociobiologist Sarah Blaffer Hrdy, whose new book touts the importance of multiple caretakers.

Published May 11, 2009 10:45AM (EDT)

For as long as she's been a sociobiologist, Sarah Blaffer Hrdy has been playfully dismantling traditional notions of motherhood and gender relations. In 1981's "The Woman That Never Evolved," the newly minted Harvard Ph.D. blasted a hole in the dominant model of sexual selection, in which hypersexual males pull out all the stops to impress passive females. Despite the snickers of her male colleagues, Hrdy maintained that women are subject to sexual selection, too: Females apes, it turns out, frequently compete with each other for male attention, trick males into copulating with them, and engage in sexual activity for pure pleasure. Later, Hrdy's monumental "Mother Nature," published in 1999, thoroughly refuted the idea that there is any such thing as maternal instinct: Mothers in nature often abort fetuses, favor healthy babies while nudging runts away, and even commit infanticide so that they can try to breed again under better circumstances.

Now a professor emeritus at the University of California at Davis, Hrdy is back with another book, "Mothers and Others," and another big idea. She argues that human cooperation is rooted not in war making, as sociobiologists have believed, but in baby making and baby-sitting. Hrdy's conception of early human society is far different from the classic sociobiological view of a primeval nuclear family, with dad off hunting big game and mom tending the cave and the kids. Instead, Hrdy paints a picture of a cooperative breeding culture in which parenting duties were spread out across a network of friends and relatives. The effect on our development was profound.

Unlike ape mothers, who were fiercely protective of their little ones and rarely shared them with anyone, early human mothers needed help raising their uniquely high-maintenance babies. They found it in the form of what Hrdy calls "allomothers," substitute caretakers of either sex who took over for a mother while she went to work scrounging up nuts and berries to feed her family. An allomother -- anyone from a baby-mad 12-year-old girl to an altruistic great-aunt -- would feed and comfort the child, sometimes even offering a breast. These mother's helpers, Hrdy hypothesizes, undergirded human society. By forcing infants to solicit attention from a network of very different potential caretakers, those complex, community-wide nurseries spurred us to develop empathy, cooperation and what psychologists call "theory of mind," an understanding that other people have feelings and beliefs that may be different from our own.

Hrdy spoke to Salon from her walnut farm in Northern California about what we have in common with marmosets, the evolutionary argument for grandmothers, and why no mom should ever go it alone.

Why did you decide to focus on cooperative breeding in this book?

In the course of writing "Mother Nature," I realized there was no way that mothers in the Pleistocene could have reared their young without alloparental assistance. At that point, I had been working on the demographic implications of shared care, and how it meant that mothers could breed after shorter intervals and produce more young that were likely to survive. So I concluded that humans must have evolved as cooperative breeders. Although people had been thinking about various permutations of this hypothesis for a while -- it started out as "mothers must have had help from their mates," and then in the '90s people started to say that it was help from siblings or grandmothers -- "Mother Nature" was really the first book to come out and say it: We could not have evolved except as cooperative breeders.

And all of a sudden it became so obvious to me that this was how to think about Pleistocene family life. But then I started to think about another problem that was emerging, a real conundrum for sociobiology: How could humans be as other-regarding, altruistic and hypersocial as they are? It led me to say, “Whoa, could these hypersocial tendencies in humans be a byproduct of youngsters growing up having to depend on multiple caretakers, having to read their intentions, having to appeal to them?”

You offer an alternative hypothesis to one commonly cited reason for large-scale human cooperation -- that we do it to make war with each other.

Yes, in the last couple of years, a particular idea to explain hypersociality has really risen to the top: that we became so cooperative because our ancestors were fighting all the time, and you needed to have in-group bonding to help fight out-group enemies. I actually don't have a problem with the argument that an outside enemy makes people more loyal to their own group, that it increases ethnocentrism, that it makes people more interested in sacrificing for the group. Social psychologists have known that for a very long time, and Darwin talks about it in "The Descent of Man."

My problem is that I don't think this explains the origins of human hypersociality. If it did, we'd have to explain why chimpanzees, which also have lethal intergroup fighting, didn't spend the last 7 million years developing hypersocial potentials to help them wipe out their neighbors. I don't think this hypothesis helps you understand why the genus Homo became so different from the other apes. And the thing that is really different between humans and other apes is how we rear our offspring.

Another key point in your book is that many early human societies were not strictly patrilocal, as many scientists tend to assume. Instead, mothers often stayed close to their own kin, which allowed them to tap a large pool of willing allomothers.

Yes, I assume that the shift toward patrilocal residence patterns was fairly recent in human history -- but remember that when I say fairly recent, I mean in the last 15,000 years. I know people are going to say that I'm a Pollyanna, that I'm denying how warlike and patrilocal humans have been. But I'm just saying that this was relatively late in history. It's not that we weren't potentially violent in the Pleistocene. It's just that we had nothing that was worth fighting for. Even stealing women and fighting over them wasn't very helpful if the groups that did were not going to be able to rear surviving offspring. Those groups were going to be at a disadvantage compared with the groups that got along with their in-laws and let them help raise the kids.

So I think being able to move bi-locally, moving to be with mother's kin or father's kin depending on where the resources were (including alloparental caretaking resources) was initially a big advantage. But at the end of the Pleistocene, lots of things started to happen at around the same time. You had a shift from mobile bands of hunter-gatherers to more complex bands of hunter-gatherers: larger, more sedentary, more stratified. Populations were starting to build up. And with the Neolithic, about 12,000 years ago, you get herding, domesticated animals, horticulture, agriculture. This led to massive increases in population. People had territory and livestock and stored food that they needed to protect, and of course, once you have property to fight over, you get a more patrilocal system. But I'm assuming that was relatively late in human history.

Where did the term "alloparent" to refer to the mother's helpers come from?

I was one of the first people back in the '70s to write about the importance of conspecifics -- members of the same species other than the mothers -- rearing offspring, but at the time I was using the very technical primatological term "aunties and uncles." And I was writing a paper in a seminar for Edward O. Wilson, and he said, "You know, Sarah, this won't do." And so it was actually Wilson who coined the term "alloparent," because he felt we needed something a little more dignified than calling them "monkey aunts and uncles."

You see grandmothers as allomothers who are particularly crucial to children's survival.

Kristen Hawkes really developed this theory in a paper she wrote called "Hardworking Hadza Grandmothers." She found that these old hunter-gatherer women were working much more efficiently and single-mindedly at collecting berries and nuts than any other women. And there are photographs in my book of langur grandmothers and great aunts just taking tremendous risk to defend infants from aggressive males, which suggests that in some social systems, these older females have a strongly altruistic intent. The hypothesis is that selection pressure for human females to go on living for so long after menopause is because of the special help and provisions that these old women could provide to younger kin, their younger daughters and nieces who were still reproducing.

It turns out that humans and marmosets have a lot in common, breeding-wise.

Yes, they're the only primates to engage in full-fledged cooperative breeding. I use this phrase because I want to separate out the species in which alloparents were actually providing significant food to children, in which they would actually come and volunteer this food. And it's so impressive, because … well, if you want to get your hand bitten, try to take food away from an animal. Animals do not typically go around giving food to others, especially not somebody else's offspring. And marmosets, they're bringing the best food items -- protein-packed lizards and little frogs that are costly to catch, very important pieces of protein -- to unrelated babies.

What about what you call the "dark side" of cooperative breeding?

In other primates there has to be something really, really wrong for a mother to abandon her child. Even if her baby is dead, she'll carry it for days. But in humans, abandonment of children after birth is actually fairly common across all societies when mothers don't have access to birth control and when they don't have access to allomaternal care. They bail out right after birth, in the first 72 or so hours, and the only other primates that do this, again, are marmosets and tamarins, who are also cooperative breeders sensitive to social support.

Your experiences in the field of anthropology have obviously had a strong impact on you, not just personally but also in the kind of research you have chosen to do, starting with your struggles early on to get more attention paid to sexual selection in women. Do you see yourself as a feminist scientist?

My definition of a feminist is someone who believes in equal opportunity for both sexes -- or, in a scientific context, paying equal attention to both sexes. When I first started out in biology, the explanatory paradigms were so male-focused that in order to do better science, I had to become a feminist. Early evolutionary theory was totally male-centered, but you can't understand what males are doing without also understanding the selection pressures on females, just as you can't understand females without understanding males.

The first scientists to study motherhood were all men, and they had a big stake in what they saw as the all-encompassing charity of women, the belief that women would just give their lives to their children wholeheartedly. As a young scientist, I went to India to find out why males in one species of monkeys were committing infanticide. I started with the hypothesis -- this is what people thought at the time -- that this was a response to population density, that it was a pathological behavior caused by animals' response to overcrowding.

I discovered that this was wrong and that this was an adaptive strategy for males entering the breeding group from outside, that it was their way of increasing their own opportunity to breed. I could empathize with these female langurs: Here they were, and every 27 months or so, a male would enter the breeding group and try to kill her infant. So of course I started to think: What have the selection pressures on these females been, and what were their strategies for coping with infanticide? And that just opened up a whole new area of study for me. But I'm not rejecting Darwinian theory. I'm trying to expand it.

Your book is called "Mothers and Others," but you also discuss fatherhood quite a bit.

Absolutely -- fathers are the critical "others." Because I am identified with feminism to a certain extent, people who don't read my book assume that I'm dissing fathers. But fathers are tremendously important. The thing about fathers isn't that they don't have a lot to contribute but how conditional their paternal investment is. They might not be willing or able to invest because they don't earn a good salary or they didn't have a good day hunting. It's funny to compare humans to, say, titi monkeys, where fathers are so important that mothers can't actually rear children without them, and the father's top priority in the whole world is to be near his offspring. Given how much help human mothers need, it's kind of a paradox that human fathers aren't so automatically caring. And I think the reason they're not is because we evolved as cooperative breeders, so even if a father dies or defects or has bad luck hunting, mothers can rely on alloparents for help.

What are a few concrete recommendations you can offer out of the huge amount of anthropological research contained in your book? How can we harness the power of alloparents to improve outcomes for real-life children?

You know, Publishers Weekly did a summary of "Mothers and Others," and I was irritated because they said I was rejecting the idea of the mother's importance. But I'm not.

What I'm saying is that human mothers are unusual in how much support they need. I'm also trying to expand the concept of what children need to include other people as well as mothers. Mothers need a lot of social support, and having more than one caretaker is very, very useful. When parents are getting divorced and the father and the mother are fighting over custody, that's so selfish. There's no way a child can really have too many allomothers. Even if the mother is mad at the father, she should want him involved. Children develop best in secure social environments, and security includes turning to lots of different people and knowing they are there for you. And since daycare is here to stay, we need to think a lot harder about how to make it better by incorporating attachment theory, making it small-scale and having consistent and responsive caretakers. But these aren't brilliant points. These are just obvious.

By Julia Wallace

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