Wednesday, April 16, 2008 - Posts
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Six years ago, I wrote about the science and ethics of incest ("The Love That Dare Not Speak Its Surname"). At the time, a study showed that having a child with your first cousin raised the risk of a significant birth defect from about 3-to-4 percent to about 4-to-7 percent. The authors concluded that this difference wasn't enough to justify genetic testing of cousin couples, much less bans on cousin marriage.
Now the incest taboo has taken another hit. Ecologists Kelly Zamudio and Chris Chandler have published a study in Molecular Ecology on sexual selection among spotted salamanders. From this and other research, Science News reporter Ewen Callaway has teased out a fascinating theme: Incest, apparently for sound Darwinian reasons, is surprisingly common in nature.
Through interviews with biologists and ecologists, Callaway looks at several cases. Among spotted salamanders, DNA analysis shows inbreeding "at the level of first cousins, on average. Despite having hundreds of possible mates to choose from, females tended to fertilize their eggs with sperm from related males." Another study found that "Japanese quail prefer first cousins over brothers and sisters and over less-related birds." Among ambrosia beetles: "Brothers and sisters tend to mate." A comparison over two generations of mating found that "inbred beetles fared no worse than outbred insects, and the eggs produced by brother-sister pairs were likelier to hatch than the eggs of unrelated pairs."
At least one fish species similarly prefers brother-sister mating. Scientists "found that fathers from brother-sister couples spent more time, on average, defending their caves and that both parents tended to pay more attention to their kids than unrelated couples." This makes obvious sense. The ecologist who supervised the study reports, "Couples which are full siblings are more cooperative in brood care. ... [T]he males and females stay with the offspring for several weeks and guard them—they defend them—and there's less aggression between full siblings."
These aren't the only rationales for inbreeding. Paraphrasing a Cambridge biologist, Callaway notes, "Many organisms might have slight genetic tweaks or adaptations tuned to their local habitats, and too much genetic mixing with outsiders can dilute these adaptations." Among ambrosia beetles, the practice "may cement the slight genetic differences between the insects," thereby helping to "create new species."
Nor is inbreeding universally taboo among humans. A study in Pakistan found that "three out of five marriages were between first cousins." Another in India that found "one-fifth of marriages occurred between uncles and nieces and a third between first cousins." And before you dismiss this as Eastern barbarism, read up on Charles Darwin and Rudy Giuliani.
The incest taboo does have a firm biological basis. As Callaway explains, "Inbreeding ups the chances that a child will inherit two versions of a disease-causing gene." Data show higher mortality among infants born from first-cousin pairs. But beyond that range, there's evidence that breeding within the family has advantages. Two months ago, a study in Science reported "a significant positive association between kinship and fertility," with a likely "biological basis." The study found "the greatest reproductive success" among "couples related at the level of third and fourth cousins." On average, these cousins produced more kids than less related—and more related—pairs did.
The upshot seems to be that there are advantages and disadvantages to breeding with a relative, and as far as nature is concerned, the ideal course is to strike a balance. You're free to argue that incest is wrong, of course. But be careful what you call unnatural.
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One thing I hope to do more of, now that I've got this network of Web pages, is to integrate reader comments into the blog. Here's a good thread in response to yesterday's post on dog meat. Lid writes,
I like pigs just fine but dogs share a place with people like no other animal. Without dogs man could not have herded goats and sheep. Man would not have settled the Arctic before modern technology. Dogs are largely responsible for our ability to sucessfully hunt game and establish populations in arid climates. Without dogs civilization would have evolved much differently, its dispersion limited and its progress stunted.
To which Sevumar adds,
Very few people relish the idea of eating an animal they've developed a personal bond with. Because dogs are so common as pets in our culture, it's understandable that many would be squeamish about eating them. These attitudes are the result of the culture we've been born into or raised in and they vary widely from place to place. In Peru, it's common for residents of the highlands to eat guinea pigs. Many African and Asian cultures use a variety of insects in their cuisine. In many East Asian cultures, the keeping of dogs as pets is a relatively recent phenomenon, so eating them was not considered taboo. Nomads of steppe cultures regularly ate horse meat. Typically, cultures learned to make use of whatever sources of protein were available to them.
It's an interesting conversation. If you start with the logic of the first post -- that the dog's moral priority stems from its role in our history -- then the second post seems correct in pegging this as a kind of relativism. So if you come from a population that didn't rely on dogs as other populations did, you have no obligation to treat dogs as pets rather than as food.
Still, I have to agree with the first post that there's something icky about relying on dogs as our teammates and then eating them when it suits us. In fact, I'd push the point further. We didn't just team up with dogs. As a study in Science explained several years ago, we fed them, bred them, and spread them. My take on this is that through relentless genetic selection and breeding, we essentially invented the dog. We derived dogs from wolves by selecting those that excelled at interpreting our behavior and executing our assignments. To borrow the Biblical metaphor: We made a species in our image.
Objectively, going by intelligence alone, it still strikes me as irrational that we think it's more wrong to eat dogs than to eat pigs. Our compunction is purely subjective, based on our current or past relationships with dogs. But maybe this is one of those cases that suggests we should respect subjectivity (or, more precisely, intersubjectivity -- somebody stop me before I start quoting Habermas) as a basis for ethics. Not only is our relationship with dogs deeply enmeshed in history - arguably the most objective thing there is among people - but that history includes our creation of dogs. The nature of dogs is that we made them to suit ourselves; so if our aversion to eating them arises from the same basis, then it's based -- objectively, you might say -- on their nature.
All this philosophy has my head spinning. I'm gonna go find a simpler topic for my next post. Somebody else carry the ball from here.
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