Eve: How the Female Body Drove 200 Million Years of Human Evolution

Bohannon imagines a big cat in southern Africa killing and dragging a dead hominin into her den two million years ago. She starts eating the dead hominin’s brain in the safety of the den, savoring the large brain’s taste. She does this and nurses her kittens, unaware that her descendants will become pets for the hominin’s descendants. Bohannon then details the brain growth that allowed hominins to become smarter, more social, and able to better control their fertility. She explains that she was reluctant to add to the topic of human brain evolution but must do so to address whether there are significant differences in male and female brains. She states that of all mammals, humans have the least significant brain differences based on sex. She then states that she must address the sexist ideas about female brains to judge their accuracy.

Bohannon first challenges the idea that men are smarter than women. She explains that people tend to associate being smart with problem-solving, frequently using the IQ test to determine intelligence. While both male and female individuals tend to have equal IQs before age 15, male individuals tend to have higher IQs after puberty. While IQ tests are given great emphasis and IQs are shown to be hereditary, they are also controversial because white Americans tend to score higher than African Americans unless there is a control for income. Bohannon thus hypothesizes that social and economic stress play an important role in IQ, with more advantaged Americans scoring higher than less advantaged Americans. She also says that studies have shown that male individuals tend to do better on tests related to spatial reasoning and math, while female individuals show higher language and verbal skills at a young age. She then challenges the idea that female individuals talk more than their male counterparts, showing that female individuals speak less in classrooms and professional settings. The stereotype likely emerges from young female individuals developing language skills and a longer vocabulary earlier. Likewise, female individuals tend to have higher reading and writing skills than male individuals. Regardless of sex, however, reading and writing are complex tools that come with humans having a large brain.

Bohannon then challenges the idea that female individuals are more emotionally and psychologically fragile than male individuals. She addresses the myths believed by Europeans about hysteria and its origins in the uterus—which they also believed moved. She then addresses the idea that female individuals are more emotional around their menstrual cycles and explains that the fluctuation of sex hormones during menstruation and pregnancy can affect female individuals’ moods. Furthermore, she discusses higher rates of female clinical depression and hypothesizes that much of it is due to female and male individuals showing depression in different ways. Male individuals tend to show depression more outwardly through emotions such as anger, whereas female individuals are more likely to internalize their depression, express emotions such as sadness, and harm themselves. Depression can also present itself during pregnancy, the postpartum stage, and menopause due to the fluctuation of hormones. Bohannon says that male and female individuals are equally as likely to develop psychiatric disorders, though they are more likely to be diagnosed with different ones. People assigned female at birth, for example, are more likely to be diagnosed with anxiety and mood disorders, while people assigned male at birth are more likely to be diagnosed with schizophrenia and drug and alcohol addictions. They are equally as likely to be diagnosed with obsessive-compulsive disorder, however. She then questions the notion of female fragility by examining suicide rates. While there are higher rates of suicide among male individuals, female individuals may contemplate suicide equally or more; however, that fact alone might not tell the full story. Some believe that this is because female individuals are more likely to have a strong social support system than male individuals, but this is not always the case.

Bohannon states that it is not simply developing a larger brain that has helped humanity survive, but it is also using that brain to adapt by learning skills such as cooking and adjusting their diets to accommodate their environments, among other changes. She also states that another factor that built humanity’s large brains was the formation of a longer childhood. By extending formative development in their young, humans allowed their children to grow even more. Young female individuals tend to develop more quickly from an early age, in some part due to male individuals being born more prematurely. Throughout development, the brain starts pruning, and it is over-pruning or under-pruning that many scientists believe causes autism. Bohannon then explains that during the third trimester of pregnancy, mothers go through a phase of brain development that nobody else does, which allows them to handle life as a mother. She explains that this is not to say that female individuals cannot be fulfilled unless they become mothers, but rather that this development is a significant evolutionary trait human mothers have. Girlhood is another neurological and socio-psychological phenomenon that female humans face. She explains that girlhood is the experience of being a female individual in a sexist society or world. This experience forces female individuals to contend with stereotypes and threats that endanger their ability to overcome limitations and underestimation. Going against rules telling those assigned female at birth that they cannot do something can have consequences. She explains that this experience also applies to transgender girls. Bohannon concludes that as the world becomes more gender-egalitarian, gender will become less important, stereotype threats will decrease, and the experience of girlhood will become more positive.