I've been rereading DR. TATIANA'S SEX ADVICE TO ALL CREATION, by evolutionary biologist Olivia Judson. As the title implies, the book is formatted like an advice-to-the-lovelorn column, with each inquiring letter from a perplexed organism used as the springboard for discussion of similar behavior in a wide range of species. The lively explorations of often bizarre sexual customs are supported by twenty-four pages of notes and an extensive bibliography. Not only are the descriptions entertaining in themselves, they delve into the reasons why evolution produced such behaviors and how they promote the survival of the species. The mating habits of "lower" animals could spark fascinatingly strange ideas for alien biology.
Suppose sentient species on other worlds shared some of those bizarre (to us) customs. If the male typically gets eaten during copulation and contentedly accepts this fate in order to nourish his beloved and their children, maybe a network of rituals would grow up around the process of his offering himself to be consumed. Maybe males would compete to become plump and nutritious. Imagine an intelligent species in which the newly hatched infants always eat their mother's body, as with some spiders. Their society would have to include a caste of caretakers and educators to bring up the young. Almost nobody would have a living mother, and the rare female who selfishly refused to let herself be devoured would be ostracized. Maybe a females' rights movement would develop an artificial infant food source to liberate mothers from inevitable death, so they could lead long, productive lives. Hive insects such as bees, of course, are dominated by females with few males, whose function is limited to mating, but among the females only the queen breeds. Terry Pratchett's Nac Mac Feegle, diminutive but bellicose fairy folk, live in a similar colony, except that the queen (or "kelda") is the only female, married to one of the males and sister-in-law or mother to all the rest.
There's a marine worm that can change its sex repeatedly throughout its lifetime. The switch depends on the size and sex of the worm's partner. When a pair stays together long-term, both eventually become hermaphrodites. Ursula Le Guin's LEFT HAND OF DARKNESS features a world where people shift between male and female depending on the random chance of which sex their current mate happens to become that month. The difference from the transsexual marine worm is that Le Guin's aliens revert to neuter for most of each month. She devised this reproductive system as a thought experiment on how a society without sex differences would work. A few Earth creatures start out as females and later transform into males; the Martians in Heinlein's RED PLANET and STRANGER IN A STRANGE LAND have this kind of life cycle. One category of organisms, slime molds and green algae among them, may have hundreds of sexes. That doesn't mean five hundred of them need to get together to produce offspring. It means each sex cell is genetically distinct from the other kinds, and there are rules as to which can pair up. The social functions of reproduction and parenting would look very different in a slime mold society from the way they work in ours. In the more conventional male and female pairings we're familiar with, imagine an intelligent species reproductively similar to seahorses, in which the male gestates and gives "birth" to the young. Or suppose we were like certain bats whose males as well as females secrete milk to feed their offspring. Either of those species would probably have a society where females, not being biologically tied down to child care, could enjoy much more independence than in traditional Earth cultures. What about a world of women who reproduce by parthenogenesis, as some animals are capable of doing? All-female societies reproducing parthenogenetically have often appeared in science fiction, such as the world of Whileaway in Joanna Russ's THE FEMALE MAN and the post-apocalyptic setting of Suzy McKee Charnas's MOTHERLINES.
Here's a page that gives an overview of numerous examples of odd animal reproductive behavior, with lots of links:The Sex Lives of Animals
Nonhuman animals have been found to engage in just about any unusual or "perverted" human sexual practice you can think of, including bestiality (copulating with a member of an unrelated species) and necrophilia. Those two habits, as the article points out, must be simply mistakes in evolutionary terms, since they can't result in reproduction. According to DR. TATIANA'S SEX ADVICE, however, the most deviant sexual custom of all, judging by its rarity is—monogamy.
Margaret L. CarterCarter's Crypt