The inbred lineage you can improve

Thanks to the efforts of geneticists the story of the extinction of the Spanish Habsburgs is now well known. They are in short a case study in the disastrous consequences of an inbred pedigree. The downsides of inbreeding are to some extent intuitively understood by all, especially consanguineous relations between first order relatives. Though I'm willing to bet that all things equal inbred individuals are not as attractive or intelligent as outbred individuals, the literature in this area for humans is surprisingly thin. A major problem is controlling for confounds; all things are often not equal (e.g., imagine if inbreeding is more common in marginal isolated communities, which is often true in the West. See Consanguinity, Inbreeding, and Genetic Drift in Italy, where it is obvious that the less developed areas of Italy had elevated rates of marriage between relatives despite Catholic discouragement of the practice). But the case that inbreeding results in the expression of deleterious recessive diseases is more straightforward. The rarer the disease, the higher the proportion of individuals who are affected who are the consequence of inbreeding. This is due to the logical fact that very rare alleles tend not to come back together in homozygote form due to the character of the Hardy-Weinberg equilibrium. If the recessive trait is caused by a minor allele with a frequency of p, p2 can converge upon zero very rapidly as p decreases in frequency. At p = 0.1 the recessive trait will express in 1% of the population (so p/p2 = 10). At p = 0.01 the recessive trait will express in 0.01% of the population (so p/p2= 100). And so forth.