[leeza]*snip*
Not funny, Bert. ~ Leeza[/leeza]
[leeza]*snip*
Not funny, Bert. ~ Leeza[/leeza]
Actually... breeding between first cousins is fairly harmless - the birth-defect rate is about the same as for unrelated parents. In western countries, it's something of a well-entrenched urban myth that first-cousin marriages result in deformed children. This is mainly due to the royal family that was almost entirely composed of haemophiliacs.
This kind of thing is also a big factor in these relationships being regarded as taboo in most western cultures (incidentally, it's illegal in 30 US states). In many parts of Asia, however, it's fairly common - and has no ill effects on the children.
A lot hinges on the founder effect, where the first generation's traits are preserved in a highly inbred line. If the founder's traits are beneficial, inbreeding is advantageous, but if it isn't (like with Hemophillia), it does more harm than good.
But the lack of genetic diversity can be dangerous in the long run if the environment drastically alters and formerly beneficial traits could become a liability. A highly inbred population cannot adapt very well to changes and are all vunerable to the same things (I remember reading that 25% of pure-bred Dalmations are born deaf).
Of course, this is with highly inbred populations. Out-breeding every couple of generations can prevent most of this from happening.