Deep sea fish assimilating males for extra sperm, flies frozen mid-coitus for 20 million years, and a walrus's penis bone... it's all part of "Sexual Nature", a new exhibition at London's Natural History Museum that spotlights the many awesomely strange forms that animal intercourse can take. Let's go on a Valentine's Day stroll through the animal kingdom, shall we?

For instance, the attractive specimen up top is a female anglerfish, which lives in some of the deepest parts of the ocean. It's one of the most sparsely populated places on the planet, and the main task for male anglerfish is just to find any available females to whom they can pass on their sperm. The problem is that anglerfish aren't always ready to spawn, and the male and female who have just found each other can't just hang around doing nothing until it's time to reproduce. That said, if they go their separate, solitary ways, there's no guarantee they'll find each other again when it is spawning season.

There's an ingenious solution to this little conundrum, but if you happen to be a male anglerfish, you probably won't like what I'm about to tell you. You see, the male fish chomps down on the female's skin...and then does nothing. The fish then start to merge, as tissues and blood vessels fuse together until it's impossible to tell where the male ends and the female begins. The male then begins to atrophy, as its organs, brain, heart, and eyes in turn shrivel up into nothing, until all that's left are his gonads, which the female keeps until she's ready to spawn.


The female anglerfish can carry with her several males to ensure she's got plenty of sperm ready for spawning season. In fact, this image actually shows two fish - the small, pipe-like structure underneath the main body of the female anglerfish is all that's left of one of her mates.

These two scavenger flies might just be the ultimate exhibitionists - they've been having sex for the past twenty million years, and they clearly don't care who watches. Of course, it helps that they're trapped in amber, a type of tree resin that can preserve insects and other small creatures perfectly for eons.


Although scavenger fly sex isn't as tough on the male as its anglerfish equivalent - the male scavenger fly gets to survive the mating process, for a start - the female still exerts a lot of control over who ultimately fathers her child. Like the anglerfish, the female scavenger fly mates with several different males and stores away their sperm for later use. After multiple insemination by various potential fathers, the female is able to actually choose which sperm will be used to fertilize her eggs.

These bones are all bacula, known colloquially as the penis bone and known even more colloquially as things way too dirty to print here. These particular bacula belong to a walrus, Great Dane, and a raccoon. The walrus baculum can measure up to thirty inches long, which is thought to be the largest of all animals. (Larger animals like whales don't have these bones.) The baculum provides rigidity that's needed during long mating sessions.

But let's not skirt the all-important question: why don't humans have bacula? No less an expert than Richard Dawkins has weighed in on this. His theory is that ancient human females preferred mates who did not need a baculum to maintain arousal, as that was an indicator of general good health. Males with the blood pressure needed to mate without a baculum were likely to be free of any major physical or mental weaknesses, which made them better reproductive candidates.

Another theory is that the type of mating humans prefer doesn't really require a baculum. The bone is most useful when the animals mate in one long, continuous session, as it helps maximize the chance that the male will successfully impregnate the female. Once that one session is complete, the male and female animals are able to go their separate ways, confident in the male's paternity.

However, that only really works if the male knows when the female is fertile, and humans don't have any instinctual means of figuring that out. So then, the best solution is for the ancient human male and female to spend all their time together to ensure the presence of no other potential mates, and then to copulate frequently for shorter periods to ensure eventual fertilization.

These are just a few of the awesome images of animal sex on display in "Sexual Nature." If you happen to be in the London area, you can see the full exhibition for yourself, but those slightly further away can check out even more photos in this gallery over at New Scientist.