I think there is a lot of confusion over the biological reasons for preventing breeding between close relatives either human or animal. Human beings have social and cultural reasons for not marrying and having children with close relatives. Our primary justification, of course, is that the children could be double recessive in some extremely BAD gene. However, we have to be careful not to confuse our moral feelings with biology. If neither "animal" has any deleterious recessive genes, then the progeny will be perfectly healthy in every respect. And many many of us people and animals are free of horrible recessives. Those recessives that do appear are rare, and the odds of finding another are small. So, what's the big problem with brothers and sisters marrying? The truth is that such things are deleterious to society. It is actually very common in other cultures than the dominant Western for cousins to marry. However, if close relatives commonly married, it would tend to alienate outsiders, disrupt community activities, annoy the neighbors, etc. In addition, many, if not most animals will breed happily with a relative if they happen to be in season. You can see this in your own domestic pets, and if you wanted to find it among animal populations, you would not have to go far. Many primates (our near animal relatives) have social structures that minimize inbreeding. However, the overall breeding populations in these groups are still closely related. Responsible breeders have been using inbreeding or linebreeding to amplify *good* recessive traits for thousands of years. Remember a certain biblical herd of black goats which was bred from a herd of white goats? I'm sure none of these black goats ended up in psychotherapy later. Breeding problems arise when any breeder sacrifices the overall health of the animals for the sake of one or two desirable traits. This is regardless of whether the two parents are closely related, or from opposite ends of the Earth. We should not categorically condemn the respectable, and very widely used practice of linebreeding simply because we think it is icky for brothers and sisters to marry. The moral issues do not cause birth defects and psychological problems. Genes cause the birth defects --and we can control, or at least *watch* the genetics-- and SOCIETY causes the psychological problems. As for Marshall Farms, they have a lot of ferrets. A few of them are bound not to come out right every once in a while. Anyone who has barn cats knows that some of the kittens just ain't born right. Catherine Shaffer Department of Biological Chemistry The University of Michigan [Posted in FML issue 1471]