PDF Summary:Eve, by Cat Bohannon

When it comes to understanding human biology and health, medical research has historically centered on men, leaving women's unique biological needs underexplored. In Eve, Cat Bohannon examines how female biology has evolved over time and argues that this evolution has shaped not only women's bodies but also human survival and progress.

Bohannon explores the evolutionary foundations of female reproductive biology, physiological adaptations that support pregnancy and endurance, and sensory differences between men and women. She also discusses the medical consequences of male-centered research bias, from misdiagnosed heart attacks to incorrect drug dosages. Beyond medicine, Bohannon argues that prioritizing women's health and autonomy benefits entire communities economically and socially. This guide offers a look at how female biology works and why understanding it matters for everyone.

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Slow-Twitch Muscle Fibers

Slow-twitch muscle fibers are a type of skeletal muscle cell that are specialized for endurance activities. They contain a high number of mitochondria, which are the energy-producing structures within cells. These fibers also have a dense network of capillaries, which are tiny blood vessels that deliver oxygen to the muscles. Additionally, slow-twitch fibers contain high levels of myoglobin, a protein that stores oxygen within the muscle cells. This combination of features allows slow-twitch fibers to sustain aerobic energy production for extended periods of time, making them well-suited for activities that require endurance, such as long-distance running or cycling.

Bohannon also highlights that women’s fat plays a crucial role during gestation and breastfeeding. Fat deposits in the body differ somewhat, but the lipids in women’s hips, glutes, and thighs contain a large amount of LC-PUFAs. The liver isn't efficient at producing these fats, so we need to obtain most of them through our diet. Bodies capable of pregnancy need them to develop babies' retinas and brains.

(Shortform note: LC-PUFAs are a family of fats that are unusually long and flexible. They’re important for the body because they’re used as core building blocks for cell membranes and for producing signaling molecules. Innis explains that these fats are “polyunsaturated” because they have several double bonds between carbon atoms, which makes them more flexible than other fats. Some common LC-PUFAs include docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are found in fish oil and are known for their health benefits.)

Women's fat in the hip and upper leg areas generally doesn't metabolize easily. Women gain weight there first and lose it there last. But during the third trimester, when the fetus enhances its brain development and increases its fat storage, the maternal body begins extracting these unique lipids and transferring them to the fetus. The mother's system continues to absorb the specialized gluteofemoral fat throughout the initial year of nursing, which is the most crucial period for the baby's brain and eyes to develop. Some evolutionary biologists theorize that the fatty hips of women evolved specifically to supply the elements needed for human infants' large brains. As our regular diet doesn't supply enough LC-PUFAs, women begin to accumulate them starting in childhood.

Variations in Fat Distribution

This pattern of fat storage and metabolism is less common in women whose fat is concentrated around the abdomen. According to researchers, the distribution of fat in the body is determined by a combination of genetic, hormonal, and environmental factors. While the typical pattern for women is to store fat in the hips and thighs, some women have a different distribution, with more fat around the abdomen. This abdominal fat is more metabolically active and is associated with a higher risk of metabolic diseases. The reasons for this variation in fat distribution are not fully understood, but it is believed to be influenced by factors such as genetics, hormones, and lifestyle.

Female Sensory Perception & Communication

Bohannon points out that women generally have a more sensitive sense of smell than men. They're superior at picking up subtle aromas, distinguishing between them, and identifying them. Women's olfactory abilities are particularly sensitive during ovulation and pregnancy, but decline following menopause. This suggests that female sex hormones are a factor. Women’s scent receptors work more effectively than men’s, and their olfactory sensory neurons have wider responses and transmit information to the brain more rapidly. The same is the case for other mammalian species as well.

Sex Differences in Olfaction

While Bohannon claims that females have superior olfactory systems across other mammalian species, research suggests that sex differences in chemosensory systems are more complex and context-dependent. For example, Christine M. Drea, a professor of evolutionary anthropology at Duke University, has found that in some primate species, males invest more in scent production and detection, while in others, females do. These differences are shaped by social organization, mating system, and ecological conditions. Drea argues that there is no single, uniform pattern of olfactory superiority attributable to one sex across mammals. Instead, sex differences in chemosensory systems reflect the specific ecological and social challenges faced by each species.

Additionally, women’s voices can change due to hormonal fluctuations. Bohannon notes that those with naturally deeper voices typically have reduced estrogen levels. During menstruation, the laryngeal lining changes. The lining proliferates and lubricates the vocal cords with watery mucus. At ovulation, the vocal folds and voice box become plumper, more flexible, and lubricated. Following ovulation, the mucus thickens and dries, which can irritate the larynx. Singers may easily hit all the notes in their range during the ovulatory phase, but after it ends, they might struggle with volume or reaching higher pitches.

Many women observe voice changes during menopause. Their vocal range might lower by an octave in their 50s and 60s. The voice box becomes firmer and more rigid, and the vocal folds grow thicker and less pliable.

Hormones and Trans Women’s Voices

The hormone-driven changes in women’s voices that Bohannon describes don’t apply to all women. For example, trans women who begin estrogen treatment after puberty may not experience these changes. In The Voice Book for Trans and Non-Binary People, Matthew Mills and Gillie Stoneham explain that testosterone exposure during puberty causes permanent changes to the larynx, including the development of the Adam’s apple and the thickening and lengthening of the vocal folds. These changes lower the pitch of the voice. Once these changes have occurred, starting estrogen treatment in adulthood can’t reverse them or reliably raise vocal pitch. Therefore, trans women who wish to feminize their voices typically need voice and communication therapy, and sometimes surgery, rather than relying on hormone treatment alone.

Medical and Societal Consequences of Masculine Norm Bias

Next, we will discuss the medical and societal consequences of male norm bias, including historical and systemic biases in medical research, specific medical consequences of ignoring differences between the sexes, and broader consequences related to reproduction, health, and society.

Medical Manifestations of a Masculine-Centric Norm Bias

Historical and Institutional Biases in Medical Research

According to Bohannon, medical research has historically excluded women, creating biases in understanding health and medical care. For instance, women face a higher risk of fatal heart attacks because their symptoms are different than men's, so they and physicians don't recognize them soon enough. Women are prescribed pain medication more often, even though it's less effective for them, and can become addicted to it because they process drugs faster than men. Bohannon also notes that women wake from anesthesia faster than men, no matter how old they are, how much they weigh, or their dosage.

(Shortform note: While researchers agree that men and women experience pain differently, they don't agree on why. One academic paper notes that women are more likely to experience chronic pain, but men are more likely to experience acute pain. The paper also notes that women respond better to certain painkillers, while men respond better to others. For example, women respond better to morphine, while men respond better to ibuprofen. The paper doesn't mention that women metabolize painkillers faster than men, as Bohannon claims. Instead, it suggests that the differences in painkiller effectiveness are due to a combination of biological and social factors.)

They're more prone to depression and dyskinesia, a problem with uncontrollable movement, though their likelihood of experiencing Parkinson’s disease is lower. The symptoms they experience are generally distinct when affected by this condition. However, women's brains heal more quickly from head trauma because their sex hormones safeguard brain tissue and reduce the inflammatory response. In addition, women have a better sense of their constraints following illness and injury, so they engage in less risk-taking once they're discharged from the hospital. Their loved ones don't have as high expectations of them following a sickness or wound, so they have longer to recover. Bohannon highlights additional cellular distinctions based on sex.

(Shortform note: Dyskinesia is a movement disorder that can occur in people with Parkinson’s disease and related conditions. According to the neuropharmacologist Peter Jenner, dyskinesia is a side effect of medications that increase dopamine levels in the brain. He explains that dyskinesia happens when the brain’s dopamine system becomes overly sensitive to the medication, leading to excessive and abnormal movements. These movements can include writhing, twisting, or jerking motions that are difficult to control. Jenner notes that dyskinesia is a common complication of long-term Parkinson’s treatment, affecting up to 80% of patients after five years of medication use.)

Female cells die because they can't prevent cellular demise, whereas male cells perish due to a trigger prompting it. Male cells also struggle more to manage oxidative stress. Male brains experience more swelling and lesion formation at injury sites than female brains.

Sex Differences in Neuronal Cell Death Pathways

Louise D. McCullough and colleagues conducted experiments on rodent models to investigate sex differences in neuronal cell death pathways following ischemic stroke. They found that neurons derived from XX animals predominantly engaged caspase-dependent apoptotic pathways after ischemic-like injury, and these neurons were selectively rescued by caspase inhibition. In contrast, neurons from XY animals relied more on a PARP-1– and nitric oxide–dependent cell death cascade and were preferentially protected by pharmacologic inhibition of PARP-1 or neuronal nitric oxide synthase.

Specific Medical Consequences of Ignoring Sex Differences

According to Bohannon, ignoring gender variations in drug metabolism can lead to incorrect dosages and heightened addiction risks. Women process drugs in distinct ways from men, often requiring different dosages for equivalent outcomes. For example, they metabolize zolpidem more slowly, so they need a lower dose. The FDA issued guidance in 2013 that doctors should prescribe women less zolpidem.

Conversely, women metabolize painkillers faster, so they need a larger amount to achieve equivalent analgesic effects. This can lead to women consuming higher amounts, increasing their risk of addiction. Expectant women who rely on painkillers are often put on methadone to prevent fetal harm from withdrawal stress.

How Researchers Study Drug Metabolism

To determine how men and women metabolize drugs differently, researchers have conducted studies where they administer the same dose of a drug to both men and women and then take blood samples at regular intervals to measure how quickly the drug is absorbed, distributed, metabolized, and excreted. These studies have consistently shown that women often have higher blood concentrations of certain drugs, like zolpidem, for longer periods compared to men. This is due to differences in body composition, hormone levels, and liver enzyme activity. Similarly, studies on painkillers have found that women metabolize some opioids faster, leading to shorter durations of pain relief and potentially higher risks of addiction.

Broader Consequences: Reproduction, Health & Society

Beyond medical consequences, Bohannon argues that prioritizing women can boost economic productivity and community wealth. Women tend to allocate their money toward things that benefit their families and communities, such as food, clothing, healthcare, and education. They frequently support investments in public works and medical care.

Bohannon explains that educating girls increases their earning potential and reduces their fertility rate, which means fewer children to support and more resources to invest in each child. This leads to better health, education, and economic outcomes for the entire community.

The Limits of “Smart Economics”

Some feminist scholars argue that the economic benefits of prioritizing women are more complex than they seem. For example, Sylvia Chant and Caroline Sweetman argue that “smart economics” approaches that foreground women’s economic participation as an efficiency strategy risk instrumentalising women as “tools” for growth, overloading them with new responsibilities without relieving existing unpaid care and domestic work, and shifting attention away from the structural and redistributive changes needed to transform the gendered power relations that underpin poverty and inequality.

Conversely, sexism and lack of access to healthcare negatively impact the health of women and society. Bohannon defines sexism as a set of rules that control reproduction, dictating what women can wear, where they can go, who they can talk to, and when and with whom they can have sex. These rules control women's bodily autonomy, how they use their time, and their reproductive lives.

(Shortform note: Bohannon’s definition of sexism is one of many. In Down Girl, philosopher Kate Manne defines sexism as an ideology that rationalizes and maintains women’s subordinate moral status in patriarchal societies. She argues that sexism is not just about individual attitudes or behaviors but is a system of beliefs that supports and perpetuates gender hierarchies.)

Bohannon explains that sexist cultures reduce the healthcare available to women during pregnancy. In the US, women in poor communities, especially in the South and Midwest, are dying at higher rates due to reduced access to healthcare and education about health. This results from initiatives against abortion, education policies focused only on abstinence, and reductions in funding for public clinics. Consequently, women in these areas experience more frequent pregnancies, an increase in STIs, higher rates of pregnancy complications, reduced access to prenatal health services, and usually more difficult deliveries. They often get discharged earlier after giving birth, raising their chances of experiencing bleeding after childbirth and other health issues. Bad health is costly for communities over time and damages families' ability to earn money. Investing in women and girls is the most effective method to boost a community's prosperity.

Is Investing in Women and Girls Always the Best Way to Boost Prosperity?

Some argue that investing in women and girls is not always the most effective way to boost a community's prosperity. In extremely poor regions with weak institutions and stagnant overall growth, efforts to empower women and girls often have only modest effects on a community's prosperity. For example, in some parts of sub-Saharan Africa, programs focused solely on girls' education or women's entrepreneurship have struggled to create lasting economic change. These efforts often run into problems like poor infrastructure, limited access to markets, and weak legal systems that make it hard for women to turn new skills into real economic gains. In these situations, broader economic and institutional changes are needed alongside targeted investments in women and girls to create lasting prosperity.