I recently read Bitch: On the Female of the Species (2022), by Lucy Cooke. Great book, unfortunate title.
There is by now an entire bookshelf of books by women scientists and journalists examining sex and gender in animals, and gently skewering the bias of male scientists. In brief: if you ever heard that males are dominant in nature, that males are naturally aggressive and unfaithful and interested in spreading sperm widely while females are demure, concerned only with offspring, and prefer a single mate… all that was widely believed well into the 20th century, but it’s pretty much all wrong.
Nature can be unkind to females… but the females fight back, and sometimes they’re unkind to males. And sometimes it’s just mondo weird out there.
Cooke’s book is organized by overall myth, and it largely consists of descriptions of one animal after another. This makes it easy to read (I can eat up wacky animal facts like popcorn) but hard to review. So rather than review the book I’m going to list a bunch of facts from it that caught my fancy. There are a lot more in the book.
If you have a conworld, this book is a great resource for evolutionary oddities. Why not use some for your sentient species?
Ch. 1: You can’t tell a male by the “penis.”
• Moles have an enlarged citoris that looks identical to the male’s penis. Hyenas too.
• Among barklice, females are more aggressive, and have erectile ‘penis’ that inserts into a male ‘vagina’. Sperm still travels from the male into the female, through this connection.
• Spider monkey females have a long pendulous clitoris, always on display. Males tuck their penises away inside!
Testosterone is not a “male” hormone and estrogen a “female” one. Both sexes produces both, and both derive from progesterone. It’s all about the timing and relative amounts. Female hyenas produce a load of testosterone in their ovaries, which results in their ‘masculinized’ genitals.
There’s a gene called SRY, on the Y chromosome, that triggers male development— but it works in concert with 60 sex-determining genes, which exist in both sexes and most animals; they interact in very complicated ways to build either testes or ovaries. (In the 1950s Alfred Jost stated that “default” development was to produce a female, but this is now seen as naïve: it’s just as complicated to build an ovary as to build a testis.) Moles achieve their unusual anatomy with changes to just two genes.
The platypus has the same set of 60 genes, but no SRY gene— though it has no less than 10 sex chromosomes rather than our two. Females are XXXXXXXXXXX and males and XXXXXYYYYY. A different gene takes over the role of SRY.
For unknown reasons the human Y chromosome is losing about ten genes every million years, and has only 45 genes left. So we could lose the whole thing in 4.5 million years. (See chapter 10 for species without males.)
Birds and some reptiles don’t have our XY system at all; they have ZW for females and ZZ for males.
Turtles don’t rely on SRY at all: eggs incubated at 88° or higher become females, those incubated below 82° become males. There are all sorts of other environmental triggers used in various species.
Females, and estrogens, came first: at least 600 million years ago. Males appeared about 300 million years ago. As they derived from females, it’s not surprising that a lot of male function depends on estrogen.
Ch. 2: Female choice in mating
Females were assumed to be “passive” in their mate choice, but this is not true at all. E.g. sage grouses participate in “leks”, displays where males dance to attract mates. It’s hard not to focus on the males, who are doing the hard work. But the females are actively watching, and responding to their feedback is key to a male actually succeeding.
Ch. 3: Monogamy, or more likely not
Females were assumed to be naturally monogamous, while it was in the interests of males to cheat. Not so. It turns out in 90% of bird species, the females play around. Social monogamy (i.e. raising offspring together) does not imply sexual monogamy.
It was once assumed that males philander because producing sperm is cheap. Producing one sperm is cheap compared to an egg— but no male generates just one sperm at a time. In mammals, at least, the energy needed to produce one ejaculation is more than that needed to produce one egg.
Often sperm includes nutrients or other substances useful to the female— sometimes in the form of a ‘sperm packet’. This also make philandering a good strategy for the female!
Ch. 4: Eating males
You can’t get more of a picture of females in control than in species where eating the male is common. Note, this is an even better protein source than a sperm packet. Mantises are famous for this, but also many species of spiders. One spider keeper offers a tip for keeping males alive: make sure the female isn’t hungry. Some species have figured this out themselves, waiting to approach till they see the female eating. The nursery web spider takes an even safer approach: bondage. He ties up the female in silk before sex. (Don’t worry, she can free herself, but it gives him time to escape.)
Ch 5: All about genitals
Genitalia are amazingly diverse. And these days you can’t just look at penises, as biologists used to do— you have to look at vaginas.
Birds don’t normally have a penis, but some do. It’s likely that the lack of a penis is the innovation, not the opposite. Ducks have one, and often use it ruthlessly in forced copulations. But female ducks have a complex vagina, with dead end pouches. She seems to have control over these, and can divert an unwanted penis into the pouches. The result is that while 1/3 of duck matings are forced, only 2–5% of pregnancies result from forced matings.
Also, both males and females ducks have seasonal genitalia. They get larger and more complex during mating season.
Some biologists have complained that the clitoris is useless— the female doesn’t need to feel pleasure to have sex. But, all vertebrates have a clitoris, which suggests it is useful. And we can easily find species where females don’t get pregnant without arousal— if nothing else, they may just reject the male. (This is easy for animals with cloacae, since then mating requires female cooperation.) There is some evidence that orgasm promotes conception in humans. Also, vaginal contractions may be necessary to get the sperm to the egg— it often can’t do it on its own.
As a last resort, the egg itself may exercise some control over which sperm get to it. Eggs can secrete chemicals that act like a pathway, and sperm react to these differently, meaning that th egg is testing something.
Ch 6: Female care.
Only 1/10 of mammals exhibit direct male care. But 9/10 of birds do— probably tied to their lack of a penis and lactation.
For weird, look at the seahorse, of course. The female, er, inovulates the male, transferring eggs to him through an ovipositor. The male inseminates and feeds them in his pouch and eventually pushes them out in the water.
In mice, at least, caring for infants is controlled by one set of neurons, attacking them by another. Both sexes have both neuron types, and stimulating one produces the same behavior (caring or attacking) in either sex. Most animals have these neuron types too, including us.
Maternal care is by no means universal or automatic. First-time monkey mothers can be very bad at it (mortality rates for firstborns are 60% higher than for laterborns). It may be adaptive to sometimes neglect the child, especially in very stressful or low-resource situations. A kangaroo fleeing a predator sometimes ejects the near-independent joey from her pouch. This is bad news for the joey, but the mother survives, and she always has reserves: a fetus and a blastocyst held in waiting; they move to the next stage when the joey is lost.
Ch 7: female vs female.
Another myth is that males do all the fighting. The topi are African antelopes; females fight each other for the chance to mate with the top males.
Male gorillas have small testes, usually a sign of little inter-male competition— the males dominate a harem. But the females compete to mate. Females may mate outside of estrus in order to drain his sperm; or high-rank females can harrass low-rank ones to prevent them from getting pregnant.
It was once thought that only male songbirds sing. In fact 71% of female songbirds do. It’s more complicated though: European and North American female songbirds sing less. It seems female birds sing to compete with other females or to lure males. In Europe and North America, they are in the vicinity less because of migration; lacking time for competition, they concentrate instead on picking between males.
Ch 8 : Matriarchy
There are 90 species of lemur on Madagascar that are female dominant. The females frankly terrorize the males (and lower-ranking females)— all the more remarkable because they’re the same size. OTOH the males have evolved an ace: copulatory plugs, made of coagulated sperm; they don’t prevent further mating but have to be removed, and given the lemur’s very short mating period (sometimes just part of a day, once a year), it can help.
Ch 9: Menopause
The grandmother hypothesis is that active grandmothers make for healthier babies who wean earlier. This was demonstrated among the Hadza people in Tanzania.
Orcas are similar— they live to be over 60. And male offspring live with them till they die, basically. Indeed, their death rates spike if their mother dies, especially if she’s post-menopause.
Ch 10: Doing without males
Laysian albatrosses, who nest near Hawaii, often live in lesbian pairs: 39 of 125 nests. This may be because it’s a newish colony, and the females are more adventurous. Males tend to stick around where they were hatched. This was discovered because there were two eggs in the nest! But only one survives, because a bird can only brood one egg, and the partner has to go out foraging.
Or there’s the mourning gecko, also of Hawaii, which has no males at all. A gecko can reproduce all by itself— a trait shared with about 100 other vertebrates. Sex is seen as necessary for adapting to new environments, so it’s thought that asexual species are short-lived (100,000 years instead of several million). On the other hand, they can colonize a new area quickly as they can produce offspring so fast. And double OTOH, some species (like the Ambystoma salamander) can grab genes from related species. It must work: the species is 5 million years old.
Some asexual species still have (lesbian) sex— because for them only sex stimulates egg production.
Ch 11: Fluid genders and genderfluids
Gender itself is fluid and nonbinary. E.g. bluehead wrasse can be seen as having three genders: males, females, and females that turn into males. Curiously, the latter are far larger than the ‘other’ males and much more territorial. The small always-males tend to form coalitions to mate. Different conditions favor each, so the mix remains.
Chalk bass can change sex pretty much at will. This allows them to take turns laying eggs, which spreads out the burden nicely.
Most sex-changing fish start out female, but the anemonefish at least goes male to female. Curiously the process starts in the brain— the gonads can take years to catch up. A female-brained fish acts like a female and is recognized as such by other fish. In all of these fish species, the sex change is operational: you get functioning reproduction.
The hagfish is hermaphroditic and can self-fertilize, probably for good reason: it lives a very solitary life. It’s worked for 300 million years.