Evolution turned this fish into a 'penis with a heart.' Here's how.

When it comes to dating in the abyssal depths of the ocean, appearance doesn't matter much. That's fortunate for anglerfish, which resemble nightmarish fanged potatoes with a little reading lamp on top. And those are just the females. If you've never seen a male anglerfish before, you're not missing much. Measuring just a few centimeters long on average, male anglers are a mere fraction of their partners' size, and contribute a fraction of the work to their relationships. For many anglerfish species, the male's sole responsibility is to permanently latch onto an obliging mate, fuse his circulatory system with hers, then slowly allow his eyes, fins and most of his internal organs to degenerate until he becomes what biologist Stephen Jay Gould called "a penis with a heart." The male gets constant nourishment; the female gets sperm on demand. The anglerfish circle of life spins on. It's beautiful, we know. But this unique mating ritual — which biologists call "sexual parasitism" — has long stumped researchers. How could the female angler's immune system even allow such a permanent, parasitic union to occur? Humans have a hard-enough time accepting organ transplants that don't precisely match their own tissues, so how does a female anglerfish's body accept a male's (or, in some cases, up to eight simultaneous males) so willingly? A genetic study published July 30 in the journal Science finally offers an answer: Anglerfish mating is only possible because the fish have somehow evolved away some of their most crucial immune defenses...MORE

Color me as heartless.