Notes for Hrdy chapters 7 and 8

From Here to Maternity – Chapter 7

         Much of what is known about the genetics and physiology of maternal behavior comes from studying laboratory rats and mice. Studies were performed to analyze motherly instincts as being “preprogrammed.” That is, whether females are born instinctively nurturing or not.  What was observed in the mice was that “instinctive” behavior does indeed describe maternal characteristics. However, those instincts are not observed immediately after giving birth but are developed gradually.

         The nurturing “instinct” has been directly linked to a specific area of a mammal’s brain called the preoptic area of the hypothalamus. That is the area of the brain that plays a critical role in sending instructions for behaviors related to nurturing. Four genes that work like master switches are known as “Fos Genes.” These genes are found in the hypothalamus and turn on other genes that code for particular proteins and hormones such as the maternal hormones oxytocin and progesterone. However, in an experiment it was observed that even when removing “maternal” genes, the maternal hormones were still present within a normal rang, despite the mother’s initial reaction not being of a nurturing nature. These mothers would eventually learn to become nurturing according to their social environment and sensitivity to conditions such as external stimuli. That is, when a female rat is repeatedly exposed to pups she naturally becomes nurturing without undergoing the hormone changes specific to pregnancy.

         Nonetheless, by removing one of the “fos genes,” the fosB gene, scientists observed that, the essential link that triggers a series of signals from the mother’s brain to other parts of the body goes missing. In other words, the mother’s brain is not triggered to elicit maternal care towards her pups despite them sending desperate signals that should elicit automatic nurture from the mother.

         Despite females being induced into caretaking through sensitization, no allomother ever defends infants with anywhere close to the ferocity of real mothers—this is known as “lactational aggression.” Such aggressive behavior sets in during the period of a mother’s very heavy investment in her young. Apparently, the act of suckling is what triggers this aggressive behavior.

         The placenta promotes the extra production of estrogen and progesterone in order to sustain the pregnancy and to elicit motherly feelings from the mother especially during the last trimester. The placenta also helps the mother identify her own pups and it elicits nurturing responses. However, after delivery and the expulsion of the placenta, the levels of progesterone and estrogen are caused to plummet. This is when prolactin and oxytocin build up in the brain. Oxytocin takes over and induces birth contractions along with eliciting affiliative feelings for the mother to receive her new pups. Prolactin is further produced with the stimulation of suckling pups. Therefore it is considered that a mother who has given birth, or nursed babies, literally develops a different “mindset.”

         Pregnant primates experience hormone changes similar to those in mice but respond in a much less stereotyped and automatic way. The main source of this greater flexibility in primates is the activity in the newer parts of their mammalian brains, known as the neocortex. In this case, practice and learning become way more important than instincts. It was observed that monkeys deprived of opportunities to socialize and interact with babies may make neglectful, sometimes abusive, first-time mothers, but they do improve with successive infants. This is not common amongst wild primates, only ones living in captivity. This is because all female primates find babies to be fascinating, so they often want to serve as an allomother to another female, thus improving their chances of becoming a more competent caretaker. What seems to be particularly attractive to female mothers is the baby’s vulnerability, newness, their small size, their awkward way of moving, and especially their distinctive natal coats with colors that baby monkeys are born with. Still, this custom of sharing one’s baby with other caretakers is a practice that primates can afford to experience because their chances are so slim that a mother will mistake some other female’s baby for her own and nurture some alien infant at the expense of her own; but it does not preclude the possibility that she will accept a foster baby in need. Despite the fascination with babies being universal in primates, what differs between species is the willingness of mothers to let anyone else hold her newborn. Chimpanzees are the least willing to share their babies in fear of a meat hungry chimp eating her baby, while the more infant-sharing monkeys are seeking more “freedom to forage” hands free of baby. It has been observed that in the infant sharing species, babies grow faster.

         For herd-dwelling animals, where there is a greater likelihood for a mother’s milk to get diverted to a stranger while her own infants starve, a process evolved so that mothers can distinguish which baby is theirs and which ones to reject: a baby’s scent is imprinted on its mother within minutes of birth. This imprinting occurs as the baby passes through the birth canal; oxytocin is induced and makes the mother’s brain sensitive to certain smells. As the mother licks the amniotic fluid surrounding her baby, she imprints on the scents in its wool.

         In humans, there are no “fixed action patterns” universally shared with other mammals such as licking their babies, and biting off the amniotic sac. The closest to a “fixed action pattern” that occurs across-cultures is that of cleansing the baby and rubbing them with a type of oil, immediate inspection of the baby and its genitals, followed by touching the baby all over.  Much of the maternal learning in humans occurs at a subliminal level. Humans are much likelier to accept and bond with a child that is not their own. Treatment between an adoptive child and an offspring of their own is especially indistinguishable the younger the adopted baby is. In some human societies, mothers pass babies around like some infant-sharing primates do, though more often only the mother holds the newborn. What makes human females differ from female primates is in the degree of maternal care variation within the same species. Turns out that childbirth pain is experienced differently amongst women depending on their cultural background and expectations. The “immediate reaction of joy” post delivery is actually quite atypical in the general context of human experience. In fact, what is a more typical response is that of indifference. Women tend to be more guarded post delivery while they recover from the exertion of delivery. There is a matter-of-factness to giving birth. The mother doesn’t become concerned with the child until it starts nursing it, which can occur many hours later. While strong feelings of attachment to the baby don’t emerge until days or weeks following the birth. And in many cultures, formal acceptance of the infant as a new member of the community is delayed and only celebrated sometime after the birth. It has even been observed that the best predictors of whether a mother seems indifferent or actively pleased, is mostly congruent with how much social support that woman has from her community.

         Approximately half of all new mothers experience “postpartum blues” or weepiness a few days after birth. Some experts see this postpartum depression as (1) a pathological response to modern procedures that interfere with the natural mammalian process of delivery and mother-infant proximity. Another expert hypothesis assumes that postpartum depression (2) is specifically human in origin, other than mammalian or primate, and can be traced back to earlier nomadic hunter-gatherer phase of human evolution. That is, back then women could have chosen to not invest in a defective infant whereas today there is the social stigma that didn’t exist then, thus the mother develops such depression. A third hypothesis, which might be termed the (3) “vestigial lactational aggression” hypothesis, states that postpartum depression is an endocrinological by-product or left-over from an intense intolerance of others. This intolerance was once adaptive among mothers who might have needed to protect infants from predators or conspecific members of their same species. Therefore, a mother’s depression is not expressive of her desire to abandon her child but to fiercely protect it. Hormone profiles are consistent with this hypothesis. That is, women tested seven days postpartum had higher hostility ratings than the females that served as controls.

Physiology: during pregnancy, a woman’s anterior pituitary (which along with the placenta is a major producer of prolactin) increases in size by about forty to fifty percent, preparing the mother’s body for lactation. Prolactin may also be implicated in responses that make her behave more defensively to protect her young. Whether she decides to breast-feed or not, a woman right after birth has high circulating levels of the same hormones that in other mammals are implicated in “lactational aggression” (173).

Conclusion: It is not true that women instinctively love their babies, neither do other mammals. Maternal commitment has to be learned, reinforced and maintained. Nurturing needs to be nurtured. There is no separation between nature and nurture, both are needed as are the sensory cues provided by infants themselves and by other individuals in the vicinity. “Love” is not genetically predetermined or environmentally produced.

Family Planning – Chapter 8

“The more children a woman had, the fewer teeth she retained in old age” (175).

            Modern Primates rarely have more than five babies spaced four to eight years apart. After weaning, offspring become like strangers for most mammals. They even may attack their children if they see them later.

            Mothers with large litters can be discriminating about which young they care for. She might prune the weakest or smallest out and concentrate on the strongest. Monkey mothers usually have a singleton, a high cost baby. She will never discriminates because of babies weight, sex, birth order, or physical conditions that affect survival prospects. The only discriminating factor is whether or not the baby can attach itself to the mother.

            A monkey/ape mother emotionally attaches to a baby to the point of carrying around the dead body of an infant who has died. The mother leaves the corpse to feed, moving farther each time and allowing more time between visits until she eventually leaves the body. She will continue to defend the corpse even for years because sometimes babies wake up. Non-human mother primates never are implicated in their own child’s infanticide. But they might kill another baby. “No wild monkey or ape mother has ever been observed to deliberately harm her own baby” (179). Sometimes a primate mother will adopt another baby. But she will favor her own.

            Tamarind mothers usually give birth to twins, sometimes triplets. Tamarinds will seek help with child rearing from fathers and other allomothers. If short on allomother assistance, the mother will reject one or more baby. Macaque allomothers harass daughters of low-ranking mothers but tolerate their sons.

            Male chimps will kill male infants born to mothers who may have been impregnated by an outsider. But they might tolerate their daughters. Under extreme circumstances, monkey/ape mothers will abandon their babies. But abandonment is dependent on the mother’s status and conditions. She might abandon her baby because of the arrival of an infanticidal male entering the group. Sometimes a mother must decide between leaving the group and leaving her baby because of an infanticidal male.

            Pleistocene humans lived at extremely low population densities with a slow rate of growth – never more than 10,000. Why such a slow growth? The infanticide rate was typically fifteen deaths for every fifty live births. During this time infanticide might have been as high as 40%. “Infanticide was culturally sanctioned, even regarded as a duty under certain circumstances” (184). But even infanticide is not enough to keep the population that low. There must have been a delayed maturation (a long delay between first menstruation and the point when a woman actually becomes fertile) plus a long interval between births.          

            Better-nourished human females reach menarche sooner, conceive earlier, and reach full body size sooner. In chimps, adolescent subfertility lasts anywhere from six months to three years. Young female chimps may use their sexual swellings to permit safe travel through hostile areas. A female can wander while she decides where to settle and breed. By fifteen years old a chimp has her first baby

            Better-nourished human girls have recently been able to conceive closer to twelve than twenty. Human menarche varies depending not only on where a girl was raised but also where her ancestors grew up. Even on the same diet, daughters of Southeastern Europe reach menarche earlier than Northwestern Europe. The reason is not yet known. Also, social stress (possibly low status/ unpredictable resources) might delay puberty. Girls who grow up with out a father reach menarche sooner. Also they on average have sex earlier and with multiple partners. They are then less likely to end up in stable relationship. Therefore, their babies grow up with out a father and start the cycle again. But this could be just an incidental correlation.

            Monkeys in captivity who gave birth at age three were negligent to a degree not seen in the wild. Some didn’t even pick up the baby. “Abandonment almost always occurred within the first seventy-two hours” (191).

            Cercopithecine societies are composed of ranked matrilineal clans organized into rigid female hierarchies controlled by mothers and grandmothers.

            1. Daughters fall just behind moms in social status.

            2. If more than one daughter, the younger rises above older when she matures and peaks in reproductive potential. The mother enforces her younger daughter’s priority by taking her younger daughter’s side in confrontation.

            Ovulating human women prefer the scent of males who have genetically produced immunological attributes different from their own. Women on birth control that simulates pregnancy prefer the scent of those with immune systems genetically most similar to their own (brothers and fathers).

            Breast-feeding is an unreliable birth control. To be reliable a person would need to nurse several times an hour because prolactin spikes when nipples are stimulated. Exercise might also contribute to menstruation delay. “A mother who neither breast-feeds nor works out may begin menstruating again as soon as two months after giving birth” (196).

            Slings allowed mothers to carry both babies and food. This meant that men did not have to be solely responsible for food—women could gather as well. When population became sedentary, it led to higher birthrates. It also led to higher rates of infant mortality because of famines, epidemics, and war. Parts of the world where famines were rare, twinning increased. Women living on islands with lots of fish had higher rates of twinning than women living on the mainland. Parts of the world with less food had less paternal twins. Usually they only had identical twins.


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Undergrad at ODU studying sociology and French. Aspiring bioarchaeologist. Gamer. Reader. Lover.
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