A no more lucid than usual Steve Jones promotes racial mixing in the name of "incest" avoidance in the Telegraph ("Why we’re having less sex with our (genetic) relatives"):
Sir Thomas Beecham – always good for a quotation – once said that “everyone should try everything once, except incest and folk dancing”. Quite where the Morris men come in, I am not certain (although Beecham much disliked the music of Percy Grainger, known for his arrangements of English folk tunes). But when it comes to incest, people are beginning to take his advice. [. . .]
Now it is easy to pick up millions of short doubled-up differences across the whole double helix, rather than in just a few lengthy but untypical segments. A new survey of this kind involved 5,000 random (and supposedly unrelated) Europeans. It revealed hundreds of thousands of previously unknown family links among them, even if one goes back no further than ninth cousins (whose shared ancestor lived at around the time of the French Revolution).
There were, for example, around 30,000 predicted fourth-cousin pairs (a shared great-great-great-grandparent). As a result, taking all family ties into account, the person you sat next to on the bus this morning is, on average, likely to be something like your sixth cousin, which means that the two of you probably share at least one ancestor from the time of the Paris Commune.
Finns (who have a history separate from that of the rest of the continent) and Ashkenazi Jews are even more likely to have close family ties; while in parts of Pakistan, the average relationship of two random people is that of second cousins, with their common ancestor alive at the time of the fall of France.
Sir Thomas Beecham (had he ever met a Pakistani, or even a Welshman) would no doubt have been outraged. But he can begin to cheer up, for in the Western world incest (or at least inbreeding) is on the way out. The proportion of people who identify themselves as of mixed race in Britain has almost doubled in the past couple of decades, and one household in eight contains members of different ethnic origins. For about half of the nation’s children with an Afro-Caribbean parent, the other parent is white, so that on these islands the pedigrees of two continents will soon merge.
Two dictionary definitions of "
incest":
sexual intercourse between two persons commonly regarded as too closely related to marry
the crime of sexual intercourse, cohabitation, or marriage between persons within the degrees of consanguinity or affinity wherein marriage is legally forbidden.
Possibly Steve Jones (a Welshman married to a Jewess) would like to see intraethnic marriages among the English outlawed. But I can be fairly certain most English feel otherwise, and it takes extreme vileness to conflate normality (intraethnic mating) and incest.
Yes, as basic math would inform us, some degree of inbreeding will exist in any population of finite size. No, the level of inbreeding present in the British population does not represent a cause for concern (and even if it did, it would not be solved in the long run by mulattoizing Britain). Empirically, mild inbreeding (yet more extreme than seen in the typical intra-English marriage today) appears to be associated with greater fitness in Europeans:
Our results, drawn from all known couples of the Icelandic population born between 1800 and 1965, show a significant positive association between kinship and fertility, with the greatest reproductive success observed for couples related at the level of third and fourth cousins.
As for deleterious recessives, outbreeding may temporarily mask harmful alleles but provides no help in the long run.
Neel:
A second obvious genetic departure of most of the civilized world from tribal societies is the relaxation of inbreeding. A discussion of the consequences of such relaxation rapidly becomes complex, and we will consider only the simplest case, involving diseases due to completely recessive genes with quite deleterious effects, incompatible with reproduction. [. . .] When inbreeding is relaxed, as is now particularly the case for Christian communities, homozygosity for genes of this type decreases, and there should be a decrease in the diseases associated with these genes. This, however, is only temporary. Mutation pressure continues, and the gene frequency will very slowly build up, until finally the frequency of homozygotes will again come into balance with mutation pressure. However, the relative frequency of the heterozygotes in the population is now greater than before. Should this population ever revert to high levels of inbreeding, it would, so to speak, "pay the bill," i.e., the gene frequency would have risen above the frequency consistent with the new level of inbreeding, and there would now temporarily be more of whatever disease is associated with the genes in question than would be the case had inbreeding continued at the original levels. Furthermore, there is evidence from experimental genetics that the heterozygotes for these recessive genes are sometimes themselves slightly disadvantaged, so that a relative increase in the frequency of the heterozygous carriers of a deleterious recessive gene is not to the advantage of the population.
One might almost be driven to question the sincerity of Jones' concern with the genetic welfare of the British. Prospective parents can already check their carrier statuses (and/or screen embryos) for most "common" Mendelian diseases, and this sort of thing will only become cheaper and more broadly applicable in the future.
Also note that basic math doesn't cease to be true just because you mongrelize a population. Turn Britain mulatto, and (besides the fact that, again by basic math, humans as a species are obviously "inbred" -- just like every other species) only the first generation will be maximally outbred. Mate two mulattoes, and you can expect them to have both segments European or both segments African across much of their genome, meaning any benefits of heterosis received by F1 mulattoes (and none to my knowledge have ever actually been demonstrated) will be greatly reduced in the next generation. Inbreeding will also commence building up in the new mulatto population just as it would in any other population with similar a demographic profile, with lineages being lost over time.
Or possibly Jones would like to maintain high levels of immigration from Africa, which ultimately would have the effect of simply replacing the English with Africans. That again would fail to solve the (non-)problem of inbreeding -- though it would certainly solve the English problem, which would appear to be the important thing to people who share Jones' politics.
Make the entire world panmictic, and you still do not "solve" inbreeding. Basic math continues to apply. Lineages will still be lost. It's just that now when a lineage is lost, it will be lost from the entire human population. As it happens:
V.13 Avoiding Inbreeding.
Interestingly enough, the systems of “maximum avoidance of inbreeding” do not have the
lowest ultimate rates of approach to homozygosity. With the same number of individuals,
it is possible to devise circular half-sib mating systems which, although they inbreed faster
initially, have a lower rate of approach to total homozygosity. This was shown by Kimura
and Crow (1964), who treated such systems in generality. Robertson (1964) provided a more
general framework for this result. He showed that, in general, regular systems of mating
with a given number of individuals will have a lower rate of approach to homozygosity the
more closely related are the individuals who mate!
Of course, the best system of all for avoiding the loss of alleles from a population of fixed
size involves the most intense inbreeding of all. If we divide a population of size 20 into
10 full-sib lines, and keep those lines isolated from each other, we stand a good chance of
retaining a reasonable fraction of the common alleles present initially. For even though each
such line reaches fixation for an allele, different lines may well fix for different alleles. So
although each individual becomes homozygous, we can restore a good fraction of the initial
heterozygosity of the base population by crossing different lines. By contrast, a repeated
mating system which does not break the population into isolated lineages is certain to fix
for one allele or another sooner or later, however small its rate of approach to homozygosity.
[Joe Felsenstein. Theoretical Evolutionary Genetics.]
