The Nature of Mothers | The Beast Within Us | Documentary
What is mother's love? A natural instinct or an unrealistic expectation? Does it even exist? These are questions Sarah Blaffer Hrdy has spent her life researching. Scientist and mother of three, she pioneered work exploring the biological basis of motherhood. Indian Hanuman langur monkeys gave Sarah some of her first answers. Her groundbreaking theories would go on to question our old ideals about what maternal instincts are. She shares with us her vision of motherhood and its crucial role in human evolution. Reminding us that we're more intimately linked to our past than most people imagine, and that these ancient legacies must be recognized if we're to understand motherhood today.
It's odd to look back and realize that I've spent almost my entire adult life not just trying to understand who I am but trying to understand how creatures like me ever even came to be. What does it mean to be born a mammal, breeding with the ovaries of an ape, possessing the mind of a human being? What does it mean to be all these things in the body of one ambitious, modern woman filled with conflicting aspirations, adoring my children, loving my husband, wanting to work, torn in all the directions that women have always been torn, struggling to maintain my balance in a very rapidly changing world? A world very different from the world my ancestors lived in. Our bodies and minds were forged some 200 million years ago when the first true mammals appeared on Earth, but they were fashioned for a way of life very different from the one we live today.
In her research, Sarah Blaffer Hrdy draws on her own experience as a mother, her observation of animal societies, and early human lifestyles. [Hadzane spoken audio]. The Hadza people of Tanzania still live today very much as we must have lived in the early Stone Age. They're nomadic hunter-gatherers surviving from day to day on food they find foraging and hunting.
For Sarah, the Hadza give us a glimpse of our existence before farming began some 15,000 years ago. Tabu, who's 20, has just had her first baby, a boy. Elizabeth is Tabu's mother.
[Hadzane spoken audio]. It's only been ten days since Tabu had her baby. Still, she's out with her sisters and cousins, collecting wild berries and geranebee.
These little berries form a staple of the Hadza diet, along with shumuko tubers and bushmeat. [Hadzane spoken audio]. The girls daily trek to and from camp, and their low-fat diet means that young Hadza like Shiku reach puberty at around the age of 17 and that they start bearing children from about 20 onwards. This is because before a woman can get pregnant, she needs to put on a certain amount of body fat.
If you think back to young women growing up in hunter-gatherer societies, a woman wouldn't even begin to menstruate till 16 or 17 at the earliest, followed by a period of post-adolescent sterility. It would be exceedingly unlikely that she could store enough body fat to be able to ovulate and conceive unless she was surrounded by allomothers, by group members who were helping to provision her. These same people, of course, would offer her social support and help her rear her child.
A hundred kilometers south of the Hadza camp lies the Tarangire National Park. It was in an environment like this that humans first evolved. Today, the African savanna is still home to another large and long-lived mammal that gives birth to live young and breastfeeds.
We share with elephants certain physiological legacies. For example, a hormone called leptin that signals young females when it's time to begin breeding. Like us, young female elephants need to stockpile resources not just in order to grow, but also in preparation for pregnancy. Without these stocks, a young elephant wouldn't be able to carry a 22-month pregnancy to term, or make enough milk for the three to four-year period a baby needs to suckle. The more food an elephant has available, the sooner she reaches puberty. If she's fat enough, an adolescent elephant in the Tarangire becomes fertile around the age of eight or nine.
When they have enough fat on board, the fat leads to the production of a hormone, a special molecule called leptin, which we know triggers puberty and the beginning of reproductive potential. It's very advantageous for mother mammals to be able to stockpile fat in advance as if on a layaway plan so that after the long gestation period, the mother will still have enough fat on board to produce milk to support her infant. Similar biological mechanisms are at work in teenage girls. The problem is we no longer live at the tempo this clock was set for.
In Europe, over the past century, the average age of puberty in girls has dropped from 17 to 13. This change has triggered an increase in young teenage pregnancies. Today, we have young women who have carbohydrate-rich diets, a lot of body fat, not a particularly heavy metabolic load.
They're couch potatoes, who are reaching puberty, beginning to cycle as early as 12 or 13 years of age. Able to give birth at far earlier ages than psychologically and emotionally women were intended to or were designed to. What's happened today is that women are living in a completely new way. Teenage girls are not always ready to become mothers at such a young age, but modern lifestyles mean that they can give birth earlier than ever before in the history of humanity. Like many of us, Sarah was overjoyed by the arrival of her first baby. She found herself wondering where our reactions to this event come from.
Might they, too, be a legacy from our distant past? We're in Karen Bale's laboratory. She's a colleague of Sarah's. A specialist on the maternal hormone oxytocin.
One of Karen's prairie voles has just given birth. She's finishing off her placenta. Well, near the end of pregnancies, oxytocin is produced in the brain.
It comes out into the rest of the body, causing both the contractions of the uterus during labor as well as milk letdown in the mammary glands. It is also projected into the rest of the brain where it causes the initiation of maternal behavior. Many of these same processes are the ones that are acting during the formation of a pair bond or love if you will. Romantic love is actually an oxytocin effect. Yes, it is, particularly in females.
That link makes so much sense to me because when I think of how I felt when my first baby emerged, I looked at her, inspected her all over, and saw she's perfect, she's beautiful, I was in love with her. When I look at some pictures, I look at the same pictures now, she was a handsome baby, but she wasn't beautiful, but I thought she was the most beautiful thing I'd ever seen. I was in love. It's not all about love. Mammalian mothers can be ferocious if they feel threatened.
Their reactions are sparked by maternal hormones. Around the time of birth, the female becomes very aggressive, both to male strangers or really any strangers, and occasionally even to her mate. This is also thought to be related to oxytocin.
Karen, this intense intolerance for her mate reminds me of that intriguing hypothesis proposed recently in Italy to explain postpartum aggression. They argue that postpartum aggression, instead of deriving from a mother's desire to harm or not want to care for her baby, really is an ancient leftover from this protective hostility towards others. It's her extreme desire to protect her baby that makes her feel aggressive and hostile, but in a modern human context, it's so culturally inappropriate for a woman, especially a new mother, to feel aggressive or hostile that she has no way to channel her emotions and she becomes depressed. Bottling up hostility to anyone she perceives as a threat to her baby, what biologists call lactational aggression, may explain why some new mothers fall prey to baby blues.
As she settled into her new role, Sarah began asking herself more questions. In many species, both parents take turns feeding the baby, so why did breastfeeding in mammals evolve as mom's job? Sarah did her fieldwork in the 1970s. Her husband, Dan, accompanied her with his film camera.
Together, they shot several films on the Hanuman langur monkeys of Rajasthan. At the time, I had no idea how drawn into the lives of these monkeys and particularly drawn into the lives of the females among these monkeys, drawn into the lives of the mothers that I would become. I had no inkling at the time that I was about to embark on a study of mothers and mothering, and eventually, grandmothers that would really take me the whole rest of my life. After six months of gestation, female langurs give birth to an infant. They'll suckle for about a year. In terms of calories, this is the most costly phase of breeding for mothers, even more so than pregnancy, but for the baby, the cupboard's never bare.
With the origin of lactation several hundred million years ago, mothers were then able to store on their bodies the resources that they needed to transform into this white gold. This perfect nutritional and immunological substance for their babies to prosper. What this also meant was a whole new kind of relationship emerging.
A sustained relationship between a mother and her infant over time. A baby that was completely now dependent on its mother to keep him warm, safe, and provisioned. Mother's milk is not only nutritional, fresh milk can kill bacteria, virus, and intestinal parasites, germs which the baby is at risk from. It's a priceless substance for a baby's survival.
By the fourth month, a mother secretes half a gram of natural antibodies into her milk daily. Sentiments aside, we could say that given the nine months invested in pregnancy, a mother's stake in her baby's survival is high. In strictly biological terms, the cost for fathers is less. A simple sperm donation.
Mothers evolved to produce milk to help secure their investment. The survival of their costly babies. The mammalian hormone, oxytocin, goes to work again during lactation.
Transmitted in milk, it acts like a mild sedative encouraging intimacy between mother and baby. From this sustained relationship, babies learn from their mothers how to relate to their environments and other animals within it. Who's who in the social hierarchy, where their own place is.
They also learn all kinds of information about making a living. Things like how to dig a well. Elephants do this to get access to good water. Filtered by the sand, it's cleaner and cooler than stagnant river water. Important knowledge for a young elephant's survival. This kind of social savvy found in higher mammals is the product of millions of years of evolution.
Lactation made it possible by forming a strong relationship between mother and baby. As mother of three, Sarah soon discovered how needy human infants are, much more so and for longer than any other primate. Women living as hunter-gatherers wouldn't have been able to raise children on their own. Who can mothers turn to for help? In many mammals, like sheep and goats, where females are mating with a number of different males, and where females are often spending their time apart from males after they give birth, you really don't see any paternal care to speak of.
Even in domestic sheep and goats like these, where the male remains in the same pasture with the females, you don't see paternal care. Males pretty much ignore the infants. The trouble with being a male mammal is that you can never know for sure if you really are the father. Often all a male has to go on is his past relationship with the mother. Breeding histories remain recorded in male organs in a most curious form. The relative size of male testes.
If, like a gorilla, a male lives in a harem and has evolved to be so big that he can prevent other males getting access to his females, he can afford to have small testes with a low-sperm count. Instead of fighting it out, a male chimpanzee outcompetes his rivals by getting more sperm inside the female. He produces large quantities of ejaculate and copulates frequently.
Where do humans fit in this picture? Basically, they fall between the chimp pattern with virtually no paternal care and a great deal of promiscuity. The very large testes, a species with a lot of sperm competition, they fall between the chimpanzee and the gorilla with its one male mating system, and a considerable amount of males really looking out for infants. A very different approach to infants depending on the male's past breeding history with the mother. The surer the male can be that the infant is his, the smaller his testes are, and the more chance there is that he might look after him, which makes sense after all. As evolutionarily speaking, mother nature wouldn't reward him for looking after another male's progeny at the expense of his own. Even though female savanna baboons are mating with more than one male around the time of ovulation, they tend to be monopolized by one or two males.
After their babies are born, mothers tend to stay close to one or two particular male friends who are also probable fathers of their offspring, who really look out for these infants, and who are more likely to intervene, for example, if the mother is threatened by another male. One of the reasons males stay near their mates after breeding is to protect mothers and their young from other males, particularly infanticidal ones. Such mate-guarding probably paved the way for monogamy and eventually nuclear families.
The question isn't whether males can protect or help care for infants, but how mothers can motivate them to do so. Females enlist their support by forging long-term special relationships with one or two willing males, who also have a chance of being the father of her baby. This concern isn't guaranteed because even if the baby is his, a father won't necessarily take care of him. Other issues are at stake.
The problem is, to reach the same goal, namely passing their genes on to the next generation, mothers and fathers have two very different strategies. Because a father can never be sure of his paternity, in evolutionary terms, it's better for him to sire as many infants as possible in the hope that at least one will be his. [Hadzane spoken audio].
Since they demand such an investment from women, it's in mothers' interests to have fewer children with at least one making it to reproductive age. While mothers go for quality, fathers often seek quantity. Hadza hunting is a classic illustration of this ancient dilemma. Back at Camp, Peter's prize doesn't go to his wife and son. It will be handed around. In Hadza society, the more a hunter catches, the more he shares.
The goal being not to feed his family, but to burnish his prestige in the eyes of others, especially other women. Our Hadza show-offs, typically masculine. Nobody knows. Paternal investment varies enormously in humans. Whether a father helps out or not, a human being still requires an incredible 10 to 30 million calories to grow up. A woman living from foraging can't provide this alone.
When male support is lacking, mothers, be they human or otherwise, have had to look for help elsewhere. Babysitters provide precious daycare for overstretched mothers. Called allomothers from the Greek allos, meaning other, they're often young females, generally older siblings or nieces living in the family group. This one wakes the baby after its midday sleep as the matriarch leads the way to new pastures.
Now that he's on the move, the babysitter sees to it that her small charge doesn't fall behind along the way. Female elephants, especially new moms, rely heavily on allomothers, so much so that a baby's chance of survival during the first two years of life depends directly on the number of babysitters available in the family troop. Langurs too frequently use babysitters. Langurs are extraordinarily committed mothers, though they need practice. Langur mothers need to learn to mother. One of the advantages to a young female of being able to borrow and carry about another female's infant is that she can gain practice mothering through this kind of babysitting.
It's a precious experience for young mothers to be as firstborn infants suffer high mortality rates among primates in the wild. Baby langurs can spend up to half their day with allomothers who are particularly attracted to the pink-eared, black-coated new babies. The baby would probably prefer to remain with its mother, but she's never far away.
She comes back regularly to suckle him. When a baby is being carried by another female, it means that the mother is free to forage, which means she's better fed, which means she's making richer milk, which means the baby is better fed, which means her baby can grow faster and be weaned again sooner, and the mother over her lifetime can afford to produce more offspring. It's a win-win situation. The babysitter learns about motherhood, the mother has some free time, and the baby is well-fed. The same might be said of our own species.
[Hindi spoken audio] In some mammal societies and many human cultures, there are individuals even more precious to mothers than babysitters: grandmothers. In langurs, an alpha male controls a group of females he guards from other males. The danger, should he be toppled, is that the new chief will kill all the small babies the ex-alpha is likely to have sired. Remarkably, it's not the infants' mothers who come to the baby's rescue, but the troops' old females. Langurs are considered sacred in Hindu tradition, and people come to feed them every day. In fights with males over food, old females are more interested in protecting troop members and their interests than in competing for food themselves.
Their daring is admirable, but as they're too old to breed now, they have less to lose in defending their family members than a mother who can still bear young. Sarah was astonished by the behavior of one old female, in particular, in the troop she studied. In this picture, the oldest female in the troop, old Sol, she was absolutely at the bottom of the pecking order.
She was old, her teeth were worn. She was arthritic, and yet on these occasions when the chips were down, it was old Sol who would come to the fore. The male had been stalking the mother with this young infant, and Sol each time would intervene, would come between them and would charge it away. To understand the kind of risk this old gal is taking: a male langur weighs nearly twice as much as an adult female does and has dagger-like canine teeth. She is taking a real risk here. Her bravery is just extraordinary.
[Hadzane spoken audio]. Old Hadza women have a similar devotion to children. Grandma Elizabeth prepares the digging sticks and knows where to find the best spots for shumuko tubers. She's also the most effective at digging them up. [Hadzane spoken audio]. She collects more than she can eat, and the surplus goes to her grandchildren.
[Hadzane sang audio]. Humans are the only primate and one of the very few mammals, along with pilot whales and maybe one or two others, where females don't just undergo menopause but they go on living for several decades after menopause. It was often the old females who were working hardest, bringing back the most food, carrying the heaviest loads.
For Hadza children, in the vulnerable life phase after weaning, having great aunts or grandmothers on hand helps them keep their weight on and means they're more likely to survive. It's possible that it wasn't just technological innovation like fire cooking or better hunting skills that helped the human species get ahead. By giving up extra food to their grandchildren, grannies may have enabled us to become a slowly maturing species with big brains and long childhoods. Combining family life and work has always been a challenge for mothers.
Forced to make tradeoffs between their infants and their own needs. Sarah believes that while maternal instinct does exist in all mammal species, it's not automatic, and in humans especially, it needs the right context to develop. In this respect, we stand apart from our primate cousins. Like all non-human primates, langurs make extraordinarily dedicated mothers. Mothers will care for any infant born to them. It doesn't matter what sex it is.
It doesn't matter about the physical condition. A baby born with serious defects, even a comatose baby, will be carried about for days by a mother who is very reluctant to do anything but care for it. On this particular occasion, I was trying to get a closer look at the corpse. We didn't know quite what the baby had died of.
As I approached the body to try to get a better look, I learned how protective not just the mother, but the whole group is of the dead baby in their midst. I had to simply retreat very ignominiously. It was days before I was able to get a look at the by-then, quite desiccated corpse. Sarah suspected the baby had been killed by a male, a frequent occurrence in apes and monkeys.
Human women are, in fact, the only primate mothers to purposely reject, abandon, and even kill their infants. In many societies, mothers discriminate on the basis of sex. If they already have, for example, several daughters, they may not keep a daughter preferring to have a son. It is in the societies with extreme son preferences that we find the highest incidences of maternal infanticide. This practice has died out in our community, but still goes on in other communities, especially among the Rajputs. People are unhappy when a girl is born, they lose status because in India we have to give a big dowry for a girl when she marries.
If the family can't afford the dowry then the girl must be given away in bonded labor to another family in the village. Families are disappointed when a girl is born because it can mean a loss of social status. The Rajputs kill baby girls by feeding them opium diluted in water. After a while the baby dies. The other method is to put a heavy bag of sand on their chests or noses to suffocate them. The third way is to starve them.
This is how newborn girls are often killed. There's one other method. It's leaving the baby to drown in a pot of milk, but you know all these things are kept very secret. I never agreed with this old custom, but people in my village still practice it and I have never managed to persuade them to stop.
My wife and I received a lot of threats and intimidation from different people, but my wife was very strong and I was obstinate. We decided that we were going to take care of our little daughter in the best way we knew how. Killing that little girl while we both remained alive made no sense to us. [Hindi spoken audio] Mary has four children. Shija, who's eight. Shiku, who's now a mother herself, is 22.
Nyanzave, the youngest, is three, and Youngun is 12. Hadza women have a child every three to five years. They rarely abandon their children as built-in forms of birth control make it unlikely for a woman to have a baby when she lacks the support she needs to raise it. Lactation suppresses ovulation.
Breastfeeding for these women who spend a lot of energy fetching food ensures they won't get pregnant. This simple natural system prevented mothers in the past from ending up with more children than they could care for. All this changes with the emergence, about 15,000 to 10,000 years ago, of agriculture, herding, new ways of getting food that allow people to settle down. Mothers were better fed, and the metabolic load of having to walk so far to get food and carry it back is reduced. These women are giving birth after even shorter intervals than ever before. Now, this works out if there's family around to help rear these children.
In other situations, it can be quite disastrous for children born at this pace. For thousands of years, after farming began, changes in women's lifestyles often proved lethal for children. In Western Europe from the 15th to the 19th century, thousands of babies were abandoned in foundling homes under conditions so dismal that often up to 90 percent of them died. In the year 1781, 20,000 of 21,000 infants born in Paris that year were sent by their mother or left by their mother to be nursed by another woman. The mortality rates in the foundling homes could vary anywhere from 60 to 90 percent.
Obviously, with children concentrated this way and also not necessarily receiving mother's milk, you had very high rates of disease. I think what is captured in these pictures is the ambivalence that these mothers must have felt. This was not an act of violence or murder. Many of these women were desperately sorry about having to give up their babies. I think the anguish is captured.
This sad episode in Western history has been largely forgotten. Even today, maternal infanticide doesn't only happen in India. It's still going on in our own backyard. In the United States, a newborn baby is killed every day by his or her own mother. When you take into account how much help a mother needs caring for her offspring so that she can go about making a living and also provisioning those offspring, the unusual level of ambivalence that we find in human mothers makes sense. It's tempting, I think, in a culture like ours where we idealize motherhood as this state of giving, as this creature who's equivalent to a form of charity, giving of herself to her children.
This is our cultural ideal for mothers. It's tempting to view mothers who feel ambivalent about maternal care as somehow suffering from some pathology, needing help. They do need help, but not necessarily from a psychiatrist. They need social support to rear their infants. Mothers can virtually never get enough support to rear these extraordinarily metabolically and emotionally costly offspring as we produce. Being abandoned is the worst disaster that could befall a baby.
To counter ambivalence, Sarah thinks that babies might have hit on a strategy to seduce their mothers. Baby monkeys and apes are born skinny. They carry practically no body fat on them when they arrive in the world. Human babies, on the other hand, are born four to eight times fatter.
People have speculated over the years as to why human infants are born so much plumper, and in many ways to our eyes, cuter than other apes are. I have wondered if what is going on here is that the baby is arriving in the world advertising to his mother what a plump and bonny full-term healthy baby he is. Mom, I'm a keeper. Think back to the last time you or a family member announced the birth of their baby. You sent out an announcement.
Born on such and such a date, a beautiful little baby girl or a beautiful little baby boy, eight pounds, two ounces. Why on earth do we include this birth weight? It's because it's part of how we perceive the baby. It's a very ancient concern of mothers that their babies should be full-term and healthy. A far greater concern, I argue, for human mothers than it is for other apes. Of course, some of them, like my third child, Nico, just go right on getting fatter.
He looked like a little Buddha at that age. He was born a Buddha and stayed a Buddha. I had lost this picture and now I found it again.
I'm so glad. Maternal instinct is a complex response, sometimes sure, and others uncertain. One thing we can say is that it's quite definitely rooted in reality. In humans especially, this instinct can only develop and flourish when conditions are favorable, just like children.