 | Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People explores the incredible variety of our world in genetics, gender identity, and sexuality. The author, a professor of biology and geophysics, makes the fascinating science easily understandable. Symbiotic partnerships between organisms is one of many captivating aspects of the natural world explored in the book. For example, the chloroplasts in plants (where sunlight is converted into energy) “were once bacteria that lived on their own. The places within a cell where our food is broken down and converted into energy (the mitochondria) were also once bacteria existing independently.” |
Because of this, every cell in our bodies is essentially “a partnership” between elements of different origins. “If every one of our cells is a symbiosis among formerly free-living bacteria, then we are but clusters of bacteria ourselves. We’re not only descended from bacteria—we still are bacteria.”
The author makes a strong argument against a mechanistic approach to genetics, giving numerous examples of how complex and decentralized genetic expression is in real life.
 Dolly the sheep | She says the myth of genetic predetermination “stems from a desire to own and control development. If a master gene produces some trait, then anyone who owns the patent for that gene controls the trait. But if traits emerge from a committee, then what’s to own? ... One can patent a gene, but not a relationship between genes.” I was surprised to learn that Dolly, the first successfully cloned sheep, aged prematurely. The author asserts that this is because the basic premise of cloning is misguided: “The nucleus doesn’t unilaterally ‘control’ the cell. The nucleus negotiates with the cytoplasm, and if the cytoplasm doesn’t go along, the project aborts.” |
The author’s exploration of gender identity was especially impactful. She writes:
“Apart from gamete size [big egg versus little sperm] and associated plumbing, nearly every male trait is naturally possessed by some females, and nearly every female trait is naturally possessed by some males. Claims of a gender binary in humans based on small statistical differences against a background of great overlap amount to social myths.”
“Apart from gamete size [big egg versus little sperm] and associated plumbing, nearly every male trait is naturally possessed by some females, and nearly every female trait is naturally possessed by some males. Claims of a gender binary in humans based on small statistical differences against a background of great overlap amount to social myths.”
Some surprising facts:
- “The most common form among plants and in perhaps half of the animal kingdom is for an individual to be both male and female at the same, or at different times, during its life.”
- “In lots of species, especially in fish, the female is bigger than the male.” [The largest animal on our planet is the female blue whale, measuring 90-100 feet long and weighing 190-200 tons.]
- “In many species the female deposits the eggs in the pouch of the male, who incubates them until birth. In many species, males, not females, tend the nest.” [Male seahorses “give birth” to the young from their belly pouches. Male emperor penguins tend the eggs and the dad ostrich-like rhea tends the nest and chicks while the female competes for other mates.]
- “In all alligators and crocodiles, some turtles and lizards, and the occasional fish, sex is determined [not by chromosomes but] by the temperature at which the egg is raised.”
- “In spotted hyenas, females have a penis-like structure identical to that of males, and in the fruit bat of Malaysia and Borneo, the males have milk-producing mammary glands.”
An entire chapter surveys gender diversity in the more-than-human world. We learn of two male genders among bullfrogs (one sings, the other is silent), singing fish with a male gender that attracts mates by humming and one that mates by stealth, and salmon with “jack” and “hooknose” males.
 | Bluegill sunfish actually have three male genders of different sizes and different mating behaviors, as do tree lizards in the American Southwest who come in different colors as well as divergent mating styles. The side-blotched lizard in the same region has three male and two female genders, all with different coloration and behavior patterns. |
White-throated sparrows in Canada have two male genders and two female genders (with variations in the colors of their stripes). They display different behaviors and pair in different combinations. This is “genetic polymorphism, in which the body differences are not limited to colored stripes. The brain architecture of the morphs differs. … the differences among the genders extend deep into the body.”
 | And there are animals with “transgender” members: male-colored females and female-colored males among more traditionally feathered birds in forty-two species of hummingbirds. Five percent of hooded warblers in the mid-Atlantic US are females with male coloration though one male warbler was observed living as a female, “including nest building, incubating and brooding young [stereotypical female behaviors], and not singing or engaging in territorial defense [stereotypical male behaviors].” |
Numerous examples of human cultures recognize more than two genders, including Native American two-spirit people whose role in the tribe was neither male nor female; the third-gender mahu of Polynesia; and India’s third-gender hijras.
 | The book also describes nonbinary gender roles in the ancient world including eunuchs. Ancient Romans defined them as “males who lacked functioning genitals.” Some eunuchs had male genitals that “didn’t continue developing at puberty.” Others chose castration, such as the divine priestesses of Cybele who had their genitals severed in “an ecstatic frenzy.” Hard to imagine divine castration today, but we’re all products of our cultures, and other societies—whether in the past or present—have widely varying worldviews and belief systems. The idea of “sex-reassignment surgery” through castration may sound abhorrent to modern Americans, but trying to squeeze all humans into narrow male-female boxes would seem equally perverse to cultures that recognize more diversity. |
“Same-sex sexuality was part of life in antiquity, although not as a category of personal identity. Whether one did or did not participate in same-sex sexuality no more defined who a person was, and who they thought themselves to be, than does, say, an appetite for French fries instead of potato chips.”
In ancient Greece, men “could, even should have sex with one another … [but used] different positions than they did with women. By restricting the permissible positions, gay sex in ancient Greece was kept masculine.”
In ancient Greece, men “could, even should have sex with one another … [but used] different positions than they did with women. By restricting the permissible positions, gay sex in ancient Greece was kept masculine.”
 Oystercatchers | Lest we assume only human engage in homosexual behavior, the book provides many examples of same-sex engagement among animals: “lesbian” whiptail lizards, same-sex mating among the New Zealand pukeko (about 10% of sightings), male and dual-female threesomes among the Eurasian oystercatcher (about 3% of nestmates), geese (15% of monogamous pairs are male-male), and male-male swan pairs observed rising adopted fledglings with more success than female-male pairs. |
Homosexual behavior has also been observed in over one hundred species of mammals. For example, bighorn sheep live in “gay” bachelor groups, copulating with each other outside of mating season. “Same-sex mating is common among female red deer, male giraffes, female kobs, male blackbucks, male and female mountain goats, male American bison, and male African and Asiatic elephants.”
The list goes on and includes female red squirrels who sometimes engage in “joint parenting. The female squirrels take turns mounting each other, and raise a single litter of young. Although only one [fertilized] member of the pair is the mother, both nurse the young.” Dolphins also engage in well-documented homosexual mating and form male same-sex pair bonds or threesomes.
The list goes on and includes female red squirrels who sometimes engage in “joint parenting. The female squirrels take turns mounting each other, and raise a single litter of young. Although only one [fertilized] member of the pair is the mother, both nurse the young.” Dolphins also engage in well-documented homosexual mating and form male same-sex pair bonds or threesomes.
 | Primates are the closest relatives to modern humans in evolutionary terms. Japanese macaques engage in female-female courtship behavior and copulation, forming short-term relationships within the female hierarchy. Up to “14% of all matings" among lemurs in Madagascar are same-sex coupling between males. |
Humans share roughly 99% of our genes with Bonobos, a chimpanzee-like species in central Africa. Among bonobos, sex reinforces social bonds: “Daily life consists of numerous brief episodes [of sex] scattered throughout the day. Every female participates in GG [genital-genital] rubbing once every two hours or so. A sexual encounter lasts about ten to fifteen seconds.”
 | The following situations lead to Bonobo sex: Sex before meals (“males invite females, females invite males, and females invite females”); “reconciliation after a dispute” (generally female-female); when a new female joins the group (to reinforce female-female bonds); to form female-female coalitions against harassing males; in exchange for gifts (usually males give treats in exchange for sex); and for procreation. |
Evolution’s Rainbow expands our understanding of gender and sexual diversity through engaging science, thoughtful insights, and a rich treasure of examples. Highly recommended.
