Rh type and mating strategy:
There are some links at the beginning of this blog. I visit them frequently. That is not to say I believe everything I see there. One recently posted a link to a blog that asserts that nuclear energy and nuclear weapons are a hoax along with such things as the moon landing. But the hbd chick site has been spending a lot of time talking about the relationship between mating strategy and biology.
For instance there has been the suggestion that altruism will be of a different intensity and directed toward different people and that this ought to have a genetic component. I have generally been skeptical. My impression is that DNA mutations take a long time to accumulate so that evolution is generally slow. The societies discussed don’t seem to be more than about thirty generations old for the most part, so I have privately shrugged off any genetic component. On the other hand, epigenetic changes can happen much faster. Your genes are more or less like tools. Knowing when to turn them on and off is more complex than the tools themselves judging from the proportion of conserved (staying constant over long times and thus probably subject to negative selection if they change) DNA compared to the DNA in the genes. Still I think it’s fair to say that the your DNA is the blueprint of the architecture of your body. On the other hand epigenetic effects are more transient. Sort of like the furniture and decorations in the house. Some day I may have occasion to bring this up on the blog.
But the thing I have found a bit irritating is the way some of the contributors refer cheerfully to “inbred” societies and “outbred” societies. To me that is like saying people who are “related” and people who are “not related.” There is no such distinction. We are all related if you go back far enough. It is a continuous scale with no biologically significant break. Similarly we are all inbred or outbred to some degree. But my sniffiness keeps getting challenged. After a great deal of research has been posted I really do get the feeling that there are first-cousin-marrying cultures and more-distant-cousin-marrying cultures and not much in between even though in-between is the biological ideal at least in terms of fertility. (I am excluding traditional cultures. They do it right from a biological standpoint. There are many of them but numerically they are not a very big proportion of people.)
So I cudgeled my brains and recently offered this to them (and as I rather expected got no response):
We have been learning about societies with differing degrees of customary consanguinity, the social and biological causes and effects. There are some biological facts that might be of interest.
There is an antigen called Rh, if you have it on your red cells you are Rh positive, otherwise negative. Positive is a pure Mendelian dominant. The negative allele is less common worldwide. It, if memory serves, is most common in Europe, the Mid East and Africa. In eastern Asia and among Native Americans it is very rare. There was an article about gene distribution many years ago in Scientific American, maybe by Svante Pääbo, that included a map of the distribution of the negative allele in the Eastern Hemisphere.
The allele is important because, in the absence of modern medicine, if a woman who is Rh negative has a child that is Rh positive, her body will react to the antigen. The first baby is generally fine, but with subsequent Rh positive pregnancies, the maternal immune system is primed and the antibodies can reach the fetal blood. This destroys fetal red cells, but if the attack is not too bad, the fetus survives and the released hemoglobin is cleared by the mother’s circulation. After birth, however, maternal antibodies continue to break up the baby’s red cells. The hemoglobin levels rise until they damage the newborn brain. With repeated pregnancies anemia from the loss of fetal red cells throws the fetus into congestive heart failure – hydrops fetalis. The fetus or newborn may die. If the condition is severe enough the fetus may get stuck in the birth canal and the mother will die. Here is a link if you want the story in a little more detail. (http://nobabies.net/Open%20letter%20to%20Nathaniel%20Comfort%20again.html) Around the middle of the 20th century the process became understood, and now it is effectively controlled, provided one has modern health care.
It is now accepted that optimal fertility comes from marrying a third cousin. (http://io9.com/5863666/why-inbreeding-really-isnt-as-bad-as-you-think-it-is) That is oversimplifying it, but let’s go with it. So there are different biological outcomes one may expect with different degrees of habitual consanguinity. 1) Intense inbreeding: the population dies. 2) Roughly first cousin marriages: fertility is low. The value placed on the life of near kin is high. 3) Roughly third cousin marriages: high fertility. Value placed on life is low, for instance honor may be more important than life. 4) Roughly fifth cousin marriages: low fertility. Value placed on life of members of the broader community is high. 5) Roughly seventh cousin and higher marriages: fertility fails, an extraordinary value is placed on the lives of all humans, the population dies.
Now into that already harrowing mix, toss the Rh gene. If everyone is positive or everyone is negative the gene is totally benign. If the alleles are mixed, then there are going to be some brain damaged and some dead babies. There are three strategies. (We can ignore 1) and 5) above as they are doomed anyway. The first cousin strategy 2) minimizes the number of mismatched couples: cousins are more likely to have the same allele. For this reason, presumably, when Charles Darwin’s son looked into the question of whether inbreeding caused insanity he found the opposite. Cousins who married were less likely to have brain damaged children. The third cousin strategy 3) maximizes fertility but at the cost of losing a lot of young mothers. That cost is so terrible that basically it’s very rare or a non starter unless you understand the rules or have modern medicine. The fifth cousin strategy 4) has much to be said for it. Fertility is adequate but low enough so as not to lose mothers and allows for a larger pool of valued lives. The difficulty is that it is hard to set up and maintain.
The facts are clear enough. That last paragraph and the issue of what value is placed on life are my own interpretation and of course could be dead wrong. What does everybody think?
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