Of course, there were downsides, too. Internal gestation didn’t just reshape our reproductive organs, but pulled in the immune system and the metabolic system, too. As we became placental mammals, Bohannon writes, “the entire female body became a gestation engine.”Of course, humans still do produce eggs, through the process known as folliculogenesis. After leaving the ovaries, in humans, they travel to the fallopian tubes. If they are fertilized, they then attach to the endometrium, or the uterine lining, and the two entities—uterus and embryo—work together to grow the placenta. A squirrel-like creature, Protungulatum donnae, whom Bohannon calls “Donna,” may be the first creature to have a modern placenta as well as a single fused womb (smaller mammals such as mice still have two uteri and two cervixes and produce litters). This ancient uterus evolved from “a muscular, oozy organ that secreted all the stuff necessary to produce an eggshell,” Bohannon writes; it marked the moment evolution turned “the mother’s body into a combination of eggshell and nest.”
Besides her primitive uterus, Donna, who lived 67 million to 63 million years ago, had another useful evolutionary alteration—her legs didn’t splay out to the side, but ran more perpendicular to the ground, hinting at what would eventually become the upright, bowl-shaped pelvis that supports an occupied and growing uterus. Birthing live young also led to another extraordinary evolutionary step. Instead of a cloaca, the single cavity through which egg-laying mammals such as the platypus also excrete urine and feces, our ancestors went on to develop a three-holed female pelvic plan, with a vagina, urethra, and rectum. Clearly, the babies that emerged into the world sans a coating of fecal matter and its dangerous intestinal bacteria had an evolutionary advantage. (Human embryos still develop a cloaca at five weeks, which then divides into the urogenital and rectal passages by the sixth and seventh weeks; the full suite of orifices is complete by about week 20.) But even with this clever bit of engineering, as placental mammals evolved to become larger, and to gestate longer, birth became riskier. By the time Homo sapiens evolved, our highly invasive placentas put us at risk for internal bleeding. And the large size of human skulls relative to the size of the pelvic opening (a mismatch that gave rise to the memorable image of “shitting a pumpkin”) means that some sort of miracle had to occur for humans to reproduce so successfully. That miracle, Bohannon says, was midwifery.
Scientists have observed small groups of female bonobos, a female-dominated primate society, guarding a birthing mother. In several cases, they “even cupped their paws under the newborn as it came out of the mother,” instances of “bonobo midwifery.” But bonobos, chimps, and other primates have relatively straightforward births. Human birth is far more complicated: Our labors are long and involved, sometimes beginning dangerously early, sometimes well overdue. So humans, with their innate sociality and emergent tool use, invented what Bohannon calls “gynecology,” defined by her as the “continually evolving body of medical knowledge and practices” to prevent, manage, or otherwise intervene in female reproduction. This includes using herbs as abortifacients, creating gynecological tools to prevent infections or stanch uterine bleeding, or eating certain plants to enhance fertility (something that primates have also been observed doing) or guide labor. Every known human society has records of gynecology. Without this innovation, without learning to care for the wombs among us, our species, with its terribly designed reproductive system, might have died out long ago.