A Brief History of the Female Body by Deena Emera

Anything and everything I either didn’t learn, didn’t listen to, didn’t care about, or simply forgot about from 6th grade health class, all in 275-pages! Every once in a while I feel like I need to read a book of this type because of the wide variety of health and wellness classes that I teach, sometimes to reinforce the knowledge that I already have, but also to try and get a better grasp of some of the concepts, theories, hypotheses, and origin stories of why our bodies act they way they do. Dr. Emera’s book, A Brief History of the Female Body, is an excellent, intellectually stimulating read, and she does a really nice job of breaking down the science-y parts into understandable and digestible prose, and also takes care to point out that some of the things we understand about the female form are based in science and fact, and others are theories and hypothesis that have been debated for hundreds and sometimes thousands of years. At times, the book can leave the reader with a few more questions than answers, but given the complexities of anything and everything having to do with human evolution, Dr. Emera presents all of the evidence without judgement, and points us in the most likely direction of what makes sense when it comes to pregnancy, menopause, female longevity, the “Grandmother hypothesis”, and why father’s really do matter in the grand scheme of ensuring the survival of their offspring. I took a fair amount of notes here to make sure I got all the main themes down, and I can only imagine that I will come back to these notes as a reference point to talk about in exercise science class in the very near future.

• females, which in biology refers to the sex that produces eggs
• our bodies are built for reproduction
• gender, a social identity that is affected by cultural and biological features
• a child’s evolutionary motivation is to take more from its mother than what is best for her to give
• been going on and on, back and forth, for millions of years
• early humans evolved a more cooperative family life, with fathers and extended family pitching in to feed and raise children
• some traits are not adaptations at all
• bell button has no function, nipples in males
• spandrels, non-adaptive by products of the evolution and other traits that are adaptive
• traits can evolve for one purpose and then change function over time
• sexual selection was a powerful force in our evolutionary past
• Darwin, kin selection, argued in On the Origin of Species
• possible for traits to evolve that har you but benefit others if you are all of the same “stock” or family
• gene’s eye view, genes are the players competing for a spot in the next generation
• why menopause, “grandmother hypothesis”, longer live span evolved in humans because grandmothers who stopped reproducing to help feed and raise their grandkids were more successful on passing on the genes involved in these traits than women who did not
• human evolution, social cooperation involving food sharing and a division of labor
• kin selection is invoked
• hypothesis still controversial
• caring for our children can be explained by kin selection
• increase the odds that our children will succeed in life and pass down the genes
• genetic conflicts between mothers and children, major driving force behind the evolution of female biology
• humans and other mammals, biological sex is decided at conception by which sex chromosome is contained in the father’s sperm that fertilizes the mother’s egg
• mix of female and male traits, “intersex”
• hermaphrodite, biology refers to an individual that makes eggs and sperm in the same body
• not physiologically possible for a human being to be a hermaphrodite
• gender is a social identity that exists only in humans
• cynobacteria changed our planet
• reproduce and dominate for billions of years
• cloned themselves, asexual reproduction, reproduction without a partner
• new type of cell division, mitosis
• your entire body is produced by mitosis
• meiosis evolved, combines the genetic information from two different individuals
• every offspring produced by meiosis is genetically unique
• sexual reproduction generates genetic diversity, advantageous during times of hardship, yielding more genetic combinations to deal with various types of risk
• potent sex hormones, many of the same hormones active during puberty are active in the developing baby
• sex hormones influence brain development during critical windows of time
• disorder of sexual development (DSD), medical classification, over 50 conditions, difference of sexual development, intersex
• sexually reproducing organisms, insects, reptiles, plants, variation in sex determination strategies is dizzying
• many of the physical traits association with each sex don’t appear until puberty
• female and male newborns actually produce milk, about 5 percent of babies
• hormone signaling that initiates puberty reactivates a system used early in life
• brain starts talking to the ovaries again, ovaries continue development
• estrogen made from cholesterol, essential molecule from which many kinds of steroid hormones are made
• woman will small breasts is equipped to nourish her infant with just as much milk as a woman with large breasts
• not clear why pubescent bodies need to lay down fat in the breasts (and hips and thighs) at all, humans are the only mammals who do this
• lactation allows adult mammals to specialize on foods that would be impossible for their babies to catch or digest, and it gives mothers more flexibility in how they live and reproduce
• milk contains fat, carbs, proteins
• prebiotics as well, encourages the growth of beneficial gut bacteria, antibiotics, which prevent the growth of harmful bacteria
• milk is the perfect food, liquid gold
• experts now agree that breasts initially evolved for functions other than nutritional support for baby mammals
• how do we get from oily sweat to milk?
• casein genes, important source of protein, carry phosphorous and calcium, are essential for embryo development
• glands started secreting caseins, essential nutrients like calcium could have passed through the permeable eggshell to the developing embryo inside
• nipples are a safer way to transfer milk to a baby
• nutrients like casein and milk sugars passing to the baby directly from the mother’s milk glands, less need for the vitellogenein yolk genes
• explanation is a simplification
• breast change during puberty, amount of fat laid down during that is unique to humans
• according to Prum, maybe Darwin, large breasts aren’t a sign of higher reproduction potential or genetic superiority, they really evolved because they were beautiful to males
• none of the hypothesis have overwhelming support
• beyond a basic understanding, we aren’t really more knowledgeable about periods than during the ice age
• majority of placental mammals do not menstruate
• modern conversation started in the 90's
• spontaneous decidualization, first estrogen builds up, then progesterone transforms it
• endometrial cells transform into decidual cells, to get ready for pregnancy
• does not occur in most mammals
• conflict theory, greedy children and stingy mothers
• genes in children that help them take more resources from their mothers will fare better over evolutionary timescales, and genes in mothers that help them moderate access to resources will fare better than those who don’t
• spontaneous decidualization may have evolved to protect the mother in advance of invasion
• could also be a maternal move in the evolutionary negotiation between mother and child
• somewhat of a sobering view of the mother child relationship
• one consequence of having more infertile cycles in our lifetimes is a higher risk of breast cancer
• every time a cell divides, there is an opportunity for a cancerous mutation to arise
• richer diets and lower levels of physical activity thought to contribute to a higher circulating level of ovarian hormones
• may fuel reproductive cancers, PMS, more common among women living in western countries, longer periods
• modern diets, earlier menarche, or first menstrual period
• earlier menarche in better fed girls is exactly what is supposed to happen
• associated with higher risk of diabetes, metabolic disease, heart disease, certain cancers
• mismatch between our reproductive and psychosocial maturation
• increased exposure to environmental toxins
• early puberty is associated with adverse health outcomes in adult life
• biological explanation for the female orgasm has haunted philosophers, anthropologists, biologists for centuries
• no disagreement on males — tied to sperm release, they evolved to deliver sperm to females
• clitoris and penis sprout from the same region in the embryo
• most of the clitoris is not externally visible
• physiological level, orgasms are a sensory motor reflex, like a knee jerk
• more complicated, but also a reflex
• many parts of the brain become activated, neurotransmitters released, dopamine, serotonin, endorphins, all make you feel good during certain activities
• reflex lasts longer
• Symons by product account, male orgasm is under strong natural selection
• females have them because of shared development and strong selective pressure for them in males
• hypothesis met with skepticism and attack
• no correlation between orgasm rate and the number of children a woman has, debate continues
• Pavlicev and Wagner, argue that female orgasm has a critical reproductive function, including ovulation
• author hypothesizes that the contractions of the female orgasm today are a relic of their ovulation/spawning function in our fish ancestors
• likely additional pressure for the reflex to feel rewarding
• individual feel pleasure and motivate them to engage in the behaviors again
• adaptation, by product, modified trait, and a lost trait all in one — long and convoluted history
• why do we fall in love, why are we choosy?
• Darwin, idea of sexual selection, evolution of traits that enhance an individual’s ability to get mates for reproduction, even if they come at cost of reduced survival
• in species in which reproductive investment in offspring is heavily skewed, with the mother putting in most of the work, pattern often observed is that females are choosy and males are showy and competitive
• general rule about mate choice, individuals who invest heavily in reproduction tend to be choosy about their mates, presumably maximizing quality of offspring over quantity, and those who invest little tend to be showy, competitive, and indiscriminate about their mates, aiming for quantity
• Tinder, 80 percent of women swipe right on only 20 percent of men
• both women and men in our species are choosy about mates
• resources and wealth influence as well
• mate choice in many species, especially in birds, mediated by visual signals
• olfactory signals, odors convey information about potential mates and potential rivals, such as social rank and readiness to mate
• seek out who smell different, presumably to make healthier offspring with a greater diversity of MHC gene versions and or to avoid inbreeding
• sight, sound, smell all play a role in human attraction and repulsion
• individuals vary in their preferences
• people often agree on their original opinions of attractiveness, our perceptions of attractiveness change as we get to know others
• in other words, personality heavily influences to whom we are attracted
• little kinder, funnier, and more empathetic — ideas have not been formally tested
• timing is also critical during mating decisions
• women are more interested in sex during days leading up to ovulation
• more restless, senses heightened, pay more attention to their appearance at midcycle
• more fashionable clothing, more makeup
• as individuals near the time when they won’t be physiologically able to reproduce anymore, they often become less choosy about their mates
• the way individuals in a species get together across space heavily influences the process of sexual selection
• Darwin’s answer, subjective aesthetic preferences, a taste for the beautiful, “sexy sons” hypothesis
• preferences exists, indicators of genetic quality of potential mates, the “good genes” hypothesis
• evidence is thin
• MHC based odors, choose mates based on them, complimentary genes to the chooser
• mate choices in the past transformed out species physically and socially
• women across the world prefer men with greater resources and that men care more about looks, advertise fertility
• contentious explanations, sliver of the full story
• fixed but vary across individuals, based on multiple traits, don’t place the same value on each trait
• why did pregnancy evolve in such a suboptimal way
• evolved under conditions of cooperation and conflict between mom and fetus
• placenta doesn’t get enough oxygen or nutrients, which can lead to a condition called preeclampsia, most common cause of maternal death in humans
• The placenta is an organ that develops in the uterus during pregnancy. This structure provides oxygen and nutrients to a growing baby
• insulin, hormone that moves glucose from our blood into our cells, thus reducing blood sugar levels
• gestational diabetes, mothers are unable to mount an effective enough response against these placental hormones, resulting in high blood sugar, can lead to high BP and preeclampsia as well as an excessively large fetus and difficult birth
• genes from mothers and fathers have been in conflict over resources to children during pregnancy
• genes are the blueprints for building proteins, which are the workhorses of the cell
• genes are like lamps, useless without some way to control their activity
• transposons are a diverse group of genetic elements that together compose over half the human genome
• important transposon recruitments were for the origin and continued evolution of pregnancy in mammals, driving changes in maternal and fetal tissues that interact so intimately during pregnancy
• huge part in the pregnancy story
• an ancient biological basis for maternal emotions and decision making that helps explains the feelings of contradiction, co-evolutionary process
• we wean our babies earlier, but these babies depend on us for much longer
• faster reproductive rate of humans relative to that of other primates is one of the few reasons we have come to dominate the globe
• help provided by other family members, fathers, grandparents, older children, raising young children
• humans became cooperative breeders
• human history is filled with stories of infant abandonment, infanticide, sex specific preferences that have occurred on a massive scale
• decisions that human mothers make to those that all mammalian mothers make regularly
• human mothers most likely to abandon their babies are without the means to help care of them
• human mothers in the past, other group members who might have been more powerful than the mother
• humans are much less likely to abandon their infants
• breastfeeding and physical contact with our children literally change the structure of our brains to reinforce maternal behaviors
• fetus has the upper hand during most of the pregnancy
• once baby is born, power shifts back to Mom
• human babies are born too large, no other mammal suffers as we do
• birth weight is a simple predictor of newborn health, evolutionary process started with mother’s choosing to invest in slightly fatter babies over skinny ones
• imprinting disorders support the idea that genetic conflicts between family members extend well beyond birth
• cooperative system benefits children and mothers, at least until the next conflict begins
• humans are cooperative breeders
• same hormones involved in maternal behaviors — prolactin and oxytocin — are also involved in paternal and pair bonding behaviors in a wide range of species
• trait that is not exhibited by human males, infanticide
• pair bonding and paternal care maintained in humans, traits were game changers for the human species
• more investment by fathers contributed to human birth intervals shortening, childhoods lengthening, and brains expanding, allowed for the evolution of increased social, intellectual, cultural complexity in humans
• female ancestors, putting an end to infanticide and enlisting males in family life were the ultimate evolutionary tricks, increased reproductive output
• female reproductive success, species as a whole
• fathers are supposed to help, species wouldn’t be where it is today if they didn’t
• our biological makeup is an important factor influencing if and how we get sick
• humans have been living with infectious disease for as long as we have existed
• in general, females have stronger and faster immune reactions than males
• males invest most of their energy into building muscle and costly behaviors like showy aggression
• females, evolved to invest more in bodily maintenance, support long pregnancies and lactation
• female immune system sometimes hyperactive, leading to autoimmune disease
• about 8 percent of humans suffer from this, 80 percent of cases are found in women
• parts of the world with modern hygiene and sanitation, autoimmune diseases have skyrocketed
• many tropical countries, continue to have widespread worm infections, lack autoimmune disorders
• human hosts who were chronically infected with worms also benefited from dampening their own immune response against worms to avoid suffering the damage of chronic inflammation
• better hygiene and medicine allow humans to live longer, suffer less from infectious diseases, more from diseases that come with an aging body
• more from chronic and degenerative diseases than our ancestors
• natural selection works better with bigger numbers, less effective with increasing age
• women do live longer
• estrogen is protective, testosterone is damaging
• when estrogen wanes at menopause, a women’s risk of developing these diseases increases. especially heart disease
• one in five women die from heart disease, compared to one in thirty for breast cancer
• alzheimer’s is one of the only major causes of death that hits women at higher rates than men
• hormonal changes and brain changes that occur around menopause
• gender bias in medicine is a big influence here
• our adult ancestors were usually pregnant or lactating, fewer menstrual cycles, fewer cell divisions, fewer breast cancers
• men are more susceptible to developing and dying from cancer
• more larger, more cells in body, more cell divisions
• endometrium, only females possess, provides some restraint in improving cancer outcomes
• female reproductive life, simply runs out of eggs at some point
• men have sperm cells that continue to divide over their lifetimes
• female, heavily invest in fewer, high quality offspring
• we inherited our reproductive span from our ape ancestors, what changed in humans is how long we live beyond menopause
• longer life span is not just a post-industrialization phenomenon
• total life span of an organism is influenced by both internal and external factors
• if your chance of dying from external factors is low, as in humans, your genes set a slower pace of aging
• transition to menopause is a gradual process that lasts years
• medically speaking, menopause has occurred after 12 months without a period
• many factors influence age at menopause, including genetics, socioeconomics, environment, lifestyle
• genes play the largest role, age of the mother’s experience of it
• age of an older sister is also an indicator
• life was drastically different for women in our evolutionary past, diets and levels of physical activity, they likely do not experience menopause the way we do today
• grandmother hypothesis, Hawkes in the 90s studied the Hazda
• help a grandmother provides boosts her reproductive success by boosting that of her daughters
• genes of these robust and cooperative grandmothers, propagated in future generations because more grandchildren were surviving and passing on these same genes
• criticism, classic riddle of which came first: longer lives or indulgent grandmothers?
• Ellison and Ottinger, adult mortality rates went down in ancient human groups with the emergence of cooperation, food sharing, division of labor, process described as self domestication
• central premise of “reproductive conflict” hypothesis is that conflict over scarce resources was resolved when older women stopped reproducing around the time younger women started
• both ecological and social factors have shaped our biology, including our outward appearance, physiology, behavior, and life history