[geoschmo]

I think what clark is trying to say is that while inbreeding will raise the risk of some birth defects, it won't neccesarily cause problems with the population as a whole. With the lower level of medical care available to the survivors those born with them will likely die without reproducing. In fact the mortality rate as a percentage of population will likely be higher then normal just due to disease and accidents because of this. It's a cold brutal math when you think of it from our modern perspective.