In today's Inquirer, Faye Flam takes a fascinating look at incest, hermaphrodism, and shrimp. She also factors in the movie "Deliverance":

Without the males, the shrimp are stuck mating with themselves, says Weeks, and that's a problem. "That's often associated with something called inbreeding depression which is, basically... have you seen Deliverance?"

(In the classic '70s film, it's implied that inbreeding led to defects suffered by a mute banjo-playing savant.)

You can't get more incestuous than sex with yourself. Unlike asexual reproduction, which also occurs in nature and creates genetically identical clones, sex with yourself can double up copies of deleterious genes.

Say you're a hermaphrodite and you carry a gene for banjo savant syndrome, or BSS. You need two copies of the mutant BSS gene to have the disease and your cells carry just one, plus a normal copy.

But you divide your genes in half to make sperm, so half your sperm get a bad copy of the BSS genes. The same thing happens in your eggs. That means one of every four of your offspring will get two bad BSS genes and come out banjo savants. And if they're fertile, all their offspring will be banjo savants.

Preventing this kind of thing is the job of the male clam shrimp, and apparently has been for some time. All of the more than 30 known species of this creature mix hermaphrodites and males, suggesting they inherited this sexual strategy from a common ancestor before they diverged. And the fossil record indicates that was more than 24 million years ago.

I'm embarrassed to admit that even though I saw "Deliverance" several times, I utterly missed the link to BSS.

I can be so clueless and unsuspecting, though.

(I'll have to watch it again.)

MORE: Via Glenn Reynolds' link to Ann Althouse, I see that I'm on the right track:

...we won't have to talk about Iraq and terrorism and detainees anymore. Let's talk about sex.