Chapter 22
What retards inbreeding?
Before we can agree on some definitions, we must look at some evidence. Consider figure 1. We have seen the bulk of it before.
Figure 1. This is a composite of two sources, one is from the origin to “B,” which was published by Labouriau and partner and shows the effect of inbreeding in Danes as evidenced by fertility graphed against “marital radius” or the distance between birthplaces of couples. The other component was published by Sibly and team and represents a compiling of many serial field counts of wild animals. The reflection is only approximate, since the axes are different and the shape of the line where the two meet is only a guess. The horizontal line in mid graph represents zero growth.
Figure 1 is the composite of two graphs, one of humans and one of animals. The graphic is quite rough, but from the origin of the graph to point “B” on the horizontal axis is a reflection of fertility against kinship in Denmark, and from “B” to “D” reflects fertility as evidenced by population growth rate from many serial field counts of wild animals. “E” on the horizontal axis indicates an extremely low degree of kinship. The horizontal line is the zero-growth line; above this line there is greater fertility than required for replacement, and below the line there is less than needed.
The fertility curve crosses the zero-growth line in two places, “A” and “C.” I have never encountered a population that seemed to be at “A,” and although some clever worker might some day contrive one, I shall not consider it further. “C,” however is quite plausible, and I believe it happens commonly. A population in that position will have rapidly rising fertility if kinship rises slightly and a slowly falling fertility rate if kinship falls a bit. Thus, this point is inherently stable; I shall call it the point of “repose.”
A second definition will be “inbreeding.” Standard usage confines this to the range from the graph origin to about “B.” Inbreeding is always destructive. I, on the other hand, take it to mean anything from the origin to “C,” anything where kinship is greater than repose. A third definition will be “outbreeding.” I mean by that kinship less than repose – anything to the right of “C.” Common usage puts outbreeding to the right of “E.”
If you are interested in extreme outbreeding, there is an enthusiastic book, Eugene M. McCarthy, Telenothians, Nothos, Athens, Georgia 2020, which delves deeply into the matter. It might distract you during lockdown with its many stories and interesting illustrations. McCarthy does seem to like neologisms.
I have not gone far into the book, but his poster species seems to be the duckbilled platypus. It has bird-like characteristics including laying eggs and having a bill for all the world like a duck while having mammal-like characteristics including hair and milk production. It could be a crossbreed, and indeed does have some bird-like genes and I imagine mammal-like genes. In my progress so far, he has not ruled out some other mechanism for the strange animal’s origin.
I have seen the creature in a zoo, and I might add just a note to his observations. They told us that the animal never sleeps. Unless I can watch one overnight or learn as much from a highly trusted source, I cannot say for sure. Certainly, the ones on display showed no sign of resting. The salient point is based on the observation that mammals, from kangaroos to people, tend to base our locomotion on the power of the hind limbs, however modified. Birds, excepting the flightless ones like ostriches and emus, use the power of forelimbs for locomotion. Penguins walk on hind limbs and flap their forelimbs under water.
A quick glance at a platypus shows that its front legs end in webbed feet, and its tireless activity is almost completely due to the way it moves those front appendages. I cannot remember whether the hind feet are webbed, and cannot be sure I saw spurs on the hind limbs that are said to deliver poison. But those active forelimbs are unmistakable; whether this is a bird-like characteristic you be at your liberty to decide.
Be warned, if you look elsewhere or expect to be understood, you need to be quite sure or quite definite about what is meant by inbreeding or outbreeding. The advantage of this bit of verbal gymnastics is that it permits me to present the material of this book in an orderly way. This first chapter then will be about what retards inbreeding.
Among humans, the most common and most potent force reducing marrying kin is social prejudice. If you want to insult a group, and can get away with it, call them inbred. It will efficiently satisfy your desire to use venom, and unless your audience is quite alert does not require any substance. People will recoil at the very notion. J. R. R. Tolkien took such pains with his masterpiece The Lord of the Rings that he created an enormous back story, The Silmarillion, detailing how the universe of The Lord or the Rings came about. Among the many tales therein, a man is immobilized by a demonic entity and forced to watch in horror as the man’s son is tricked by the demon into having sex unknowingly with his sister and then learning the truth and experiencing the horror of that knowledge.
There you have it. This genius, call him the greatest modern story teller, could come up with nothing worse than incest.
There are laws against such incest, but I think it was Professor Robin Fox who pointed out that such laws are unimportant. People don’t want to do it anyway. There is such social prejudice against it that I am not sure but what it is more condemned than having sex with animals, something you are probably pretty sure whether you have accomplished or not.
I have a small acquaintance with scripture, but it does not extend to giving me a grasp of life in Old Testament times. I do understand that it was the first literate society. Writing had been around for a long time, but it was a field for experts. If you are carving in stone, a character that can represent two other characters should save you a moment, and the number of characters thus multiplied. But Hebrew limits itself to consonants. This tends to maintain the sense of the passage. Take the first seven words of this paragraph, looking only at the consonants: “hv smll cqntnc wth sciptr,” and compare it with looking only at vowels, “I ae a a auaiae i iue.” Most of us would have better luck puzzling out the first version than the second. So, given a knowledge of the language, and most people speak at least one, and knowing how the consonants are written, presto; you are literate. It should not take a whole afternoon.
It also demonstrated itself to be a very durable culture. There are Jews to this day; not so many other cultures trace their heritage so far back. Yes, yes, I know there have been changes, but there has been continuity as well.
Is it a coincidence that resilience and literacy go together? I’m not sure I could swear one way or the other. But that literacy has embodied what I consider to be the most powerful collection of writings I know of. I have read other sacred texts, but begging you pardon they just don’t match scripture.
One custom in biblical times was to turn the slaughter of an animal into a religious occasion. Greeks, Romans and Hebrews shared this. So possibly a feature of village life was a trip to the Temple for sacrificing to get meat for a period of time. Otherwise, perhaps villages pretty much stuck to themselves. If so, this would have nudged village toward inbreeding, and possibly each little population was in repose. Perhaps this was the secret of the cultural durability.
BUT …
When the modern state called Israel was established, one of the projects was to establish little communes called kibbutzes or if you like kibbutzim. There was the rather endearing hope that each would be reproductively isolated like the old villages might have been. But it was not to be. Youngsters growing up on the same kibbutz did not want to marry each other. Well the country solved the problem somehow, because among rich countries none has both a per capita income and a total fertility to match Israel.
All the same, the phenomenon was enough of a nuisance to attract attention and turned out to have a name, the Westermark effect. As generally understood, it means that a boy and a girl who spend a lot of time with each other before the age of six will not, as they mature, find each other sexually attractive. I confess I would have guessed a higher number of years. My own experience chatting with friends is that few indeed have much memory of their lives before the age of six. I might have put the top age of what is called “negative sexual imprinting” closer to ten.
It isn’t just people. Bateson demonstrated that Japanese quail (I suppose they are easier to work with than harpy eagles) are sexually attracted to each other if they are of moderate kinship. Moreover, and more to the point, if two otherwise mutually attractive birds from the same clutch of eggs are together as nestlings they are less attracted to each other than they are if they are separated as eggs and never encounter each other until tested in the lab. The Westermark effect thus holds for people and for birds and one can only wonder how far the effect extends if one were to test for it.
Calhoun demonstrated in caged mice behavior that indicates beyond reasonable questioning that mice in that situation mate for mouse status. They pile up their nesting choices in a preferred area of the cage in spite of the fact that there is no obvious attraction there. Assuming people are significantly status driven, and it would take a brave person to deny it, we tend to ignore the sweet, wholesome call of kinship that those quail respond to. This can be said to retard inbreeding.
At this point, we run afoul of a problem with the definitions we so laboriously specified. Status seeking can, yes, retard inbreeding, but this effect blends seamlessly into encouraging outbreeding. It is just a matter of whether the population is above or below the point of repose. So, we shall revisit status later when it is clearly in situations of kinship less than repose.
Mate choice can be influenced by personal appearance in humans and animals, but we shall stay with humans. When you look at a person you see the results of more than one process. Basically, you are looking at an organism that grew and developed under the instructions of its genes and its epigenetic markers. Of course, there are changes in appearance brought about by environmental factors. Then there are changes brought about by deliberate choices on the part of the person you are observing. And if it is a real-life observation, there may be an inadvertent reaction to your harmless glance or predatory stare. There might be clues as to status as expected in the community. All these interact such that the result is a hopelessly complex overall impression. And that impression is what, among other things nudges mate choice.
When I look at the news in this the dreadful year of one hundred one score, I see a political division that seems to be universally recognized. And it seems to me that one side tends to appear not only better kept but basically more physically sound than the other. The other looks sickly and downright ugly most of the time. You be at your liberty to choose which side is which, but appearance is another factor that might, some of the time, nudge couples in the direction of less inbreeding.