[QUOTE=groman]
Is there anything scientifically wrong with pure eugenics besides people finding it ethically icky? I mean it worked for dog breeders for centuries, I fail to see why it’s not a valid principle for humans, scientifically speaking.
[/QUOTE]
Assume positive eugenics, not negative, so as to sidestep ethics and rights issues. Assume further that we’ve found some way to effectively convince the people we think are more fit to have more children while respecting everyone’s rights and still staying within some sort of budget.
A problem that has come up with dog and cat breeders is unexpected consequences. You decide to breed for, say, folded ears (as in Scottish Fold cats). The folded-ear gene turns out to be linked to skeletal deformities. Or a cat or dog breeder might just breed for a characteristic that isn’t directly linked to a genetic problem, but end up with genetic problems because of other characteristics they’re ignoring. Hip dysplasia is much more common in purebred dogs than in mutts, and dental problems are more common in purebred cats than in moggies. There are numerous examples of dog breeds that have developed temperament problems because they were bred for looks, with temperament a secondary consideration (if at all). We could have some of the same problems with humans if we encouraged, say, intelligent people to breed- you’re ignoring some health problems (or there may be some that you don’t know about), which might end up getting worse.
You might also end up breeding for something that isn’t important in the environment the people end up in, while neglecting or discouraging something that turns out to be very important. Sickle cell trait might end up being a bigger plus than a minus if drug-resistant forms of malaria became more widespread, for example. And there are some traits that are highly valued in a culture at a given time, but might actually pose a disadvantage to the person who has them. Light skin, hair, and eyes would be an example- they make you more prone to skin cancer.
If it’s taken too far, eugenics might decrease human genetic diversity, which makes people more uniformly vulnerable to diseases.
There’s also the fact that, to increase genetic fitness, you should probably be encouraging breeding between individuals as unrelated as possible. That means interracial, cross-cultural, and interfaith marriages, which some people still have a problem with. There are some people who probably would not take it well if the government gave $X to every black/white couple who marry. There would also be a fuss kicked up by members of some groups saying this was an effort to destroy their distinctiveness.
And then, it might just not work. If the traits you’re breeding for are governed by a large number of genes instead of a single gene, selective breeding just isn’t going to do very much to encourage it without running into the monoculture problem. Or a trait might be more affected by environment than by heredity.