Going way back to before there was any such thing as an evolutionary theory that wasn’t laughably wrong, one of the favorite arguments for special creation was the alleged perfection of God’s design. Nothing so ideal and finely tuned as a hummingbird could- supposedly- possibly come from any natural process. (I suspect this was before people knew that hummingbirds have to enter a state of helpless torpor just shy of death every night just to avoid starving to death before morning.) It drove a rather interesting sort of amateur naturalism (“natural theology”) among the religious to seek out examples of the glory of God in the perfection of nature, which at least got people out and observing, and certainly strikes one as a more interesting and productive religious activity than, say, Calvinism.
You can still see this sort of thing among dedicated advocates of special creation (as opposed to people who think God created life but evolution still applies), but they’re far less likely nowadays to also be biologists or naturalists, because two hundred years after William Paley, we’ve seen… a little more of nature. The sort of nature that, with the mention of a mere genus name, can cause some of the well-informed to either crack up or lose their appetites on the spot.
My personal favorite, because it makes my inner thirteen-year-old giggle madly, is Xylocaris maculipennis. Like a surprising number of other bedbugs, Xylocaris reproductive process is “traumatic insemination”, or in layman’s terms, “he jumps on you and stabs into your abdomen with his penis when he wants to make a baby, and not through the vajayjay, either”. Because it is, basically, stabbing rape, Xylocaris mating leaves an insemination scar. If this weren’t wince-inducing enough… females aren’t the only ones to commonly have insemination scars. Males do too. Either the bedbugs simply aren’t picky and stab-rape everything that comes in range… or, as theorized, they do it because it forces some of their own sperm into the victim, so that the next time the victim male stab-rapes somebody, he might wind up passing some of his rapist’s genes along with his own. (This is considered possible because bugs have an open circulatory system. It’s also why the stab-rape thing works on the females to begin with.)
The evolutionary explanation is actually fairly simple; in other species of bedbugs (and not a small number of other arthropods), “mating plugs” are common. When a male mates with a female the normal way that doesn’t make the entomologist shudder, he leaves behind a plug that prevents any other male from mating with her thereafter. Good for him, kinda bad for her (it would be better for her to mate with a more diverse number of males to maximize the chances of a good gene combination), bad for other males. This would be about like the first nuclear tests: first stage of a subsequent arms race, for some species. The stab rape was next- you can completely bypass any mating plugs that might be there and just make use of whatever eggs might be there and unfertilized at the time. Good for him, bad for her (the stab rape is just another physical trauma for the female- she suffers the same consequences as for any injury, baby-makin’ or no), indifferent for other males. Most species that went the stab-rape way stopped there. If the theory behind the common insemination scars on Xylocaris males are correct, then the next step is stab-raping everybody in order to get your genes out as widely as possible. It is, at least, a level playing field for pretty much everybody except the females. (Nobody has yet reported a bedbug species in which the females have evolved carry pistols and Krav Maga, but I figure it’s just a matter of time.)
Vertebrates get off somewhat lighter on the Terrifying Sex front than arthropods, but not entirely. As Holly mentioned in the comments, male ducks have a nasty habit of forcing themselves on the females. (Link may not be safe for work. Do not click unless you think you can successfully explain why you’d be reading about duck phalluses to your boss.) This normally isn’t really possible for birds, since bird sex requires a delicate balancing act that makes this observer wish for popcorn and score cards, but ducks are unique in both having an intromittent organ at all (97% of birds don’t), and in having a mating platform- water- on which they can basically immobilize the female. Once again, it really sucks to be the female, because there is a fairly high rate of injury or death for the females- add in the fact that mallard ducks in particular have an oddly high rate of homosexuality, and you have the animal kingdom’s first recorded case of homosexual necrophilia. Kinky people, the next time you start thinking you’re such creatively bent little primates, remember that you were outdone in perversity by a duck. (And, possibly, a squirrel, but no one was able to get a confirmed gender ID on the victim for that one.)
Again, from a strict evolutionary perspective, it makes sense. Ducks, like many other birds, form bonded pairs to raise chicks; that’s the arrangement that benefits both partners. Males, however, can maximize their chances of getting their genes spread around by raping the females when they get the chance- and if they kill her, it wasn’t their partner anyway. (I do not know if it’s only males that haven’t scored a bonded partner that do this, or if some of the bonded males are simply very busy.) Female ducks have more to work with, anatomically speaking, than a female bedbug does; her oviducts can evolve to be simply harder to access if she doesn’t make it easy for her partner. And, they have- species with high rates of forced mating have females in which the lower oviducts are incredibly baroque… and to which the male duck genitalia is correspondingly specifically matched, for his side of the arms race. Also, it is incredibly cool that the theme song from “Mission: Impossible” just came up on my playlist.
Spotted Hyenas have a variety of “interesting” design that was obvious enough for even the ancients to observe: the females are highly masculinized, so that males and females both have a phallus. The ancients, rather confused by this in general, came to a tentative general consensus that the hyena must be able to change its sex. (Although how they reconciled this with both participants in a hyena mating having a phallus, my source does not say. Perhaps this was because most of this information was through general word of mouth rather than field observation.) They also, perhaps understandably given some other hyena traits, came to the conclusion that the entire beast was some kind of God-given allegory about… something. Something very, very wrong, be it gluttony, or treachery, or homosexuality.
The link above explains the evolutionary reasoning for the extreme masculinization of female hyenas- they are bigger, stronger, meaner, and more dominant than the males in addition to having masculinized genitalia- as a side effect of the female competition for dominance, supposedly sparked by the reproductive advantage enjoyed by the sons of the most dominant females. The masculinization was, in theory, a side effect of selection for testosterone-driven aggression. Unfortunately for the theory, female hyenas have normal levels of androgens (testosterone and its relations), and experimentation with anti-androgens had no effect on the development of the phallic-clitoris-extended vagina arrangement. (The vaginal passage runs through this structure.) Therefore, its development was probably no mere side effect of selection for aggression- which is interesting, as it makes for both an awkward way to mate and a dangerous way to give birth, with a female’s first cubs often dying during the birth, and subsequent births resulting in a nasty rupture that can take weeks to heal, leaving the hyena not only hurting, but open to infection or other complication. There are other nasty aspects to the hyena arrangement; intrasex competition is so intense that when a female gives birth to twins of the same sex, one will almost invariably kill the other. There is no good theory I’ve heard that can even come close to explaining how this arrangement came to be despite its many disadvantages… though despite the infant mortality and the dangers to the mothers, spotted hyenas are pretty successful as African predators go, so there must be something that’s simply been missed so far. Biologists becoming interested in hyenas rather than the much more popular lions is a relatively new phenomenon.
Next time I might talk about this using something other than exclusively twisted sexual arrangements of nature. But because this pleases both the inner child that liked to collect bones and the one that thought dirty jokes were hilarious, I wouldn’t count on my moving on to panda thumbs and stupid trachea tricks just yet. Not when there are still lesbian clone lizards in my yard.