Most dreaded terror.

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downloaded 12/17/17 For the whole story, go to nobabies.net and start reading summaries, papers and the source code.
Chat 1 Incest does not work the way they say it does.

1. The title is of course a pun.  This issue is an error, a fault in thinking threatening our very existence.
2. Let me give my non-standard and deliberately inflammatory definition of a baby.  When a sperm touches an egg, that moment defines the DNA, the epigenetic markers and intracellular machinery to make an individual.  If you have done something that prevents that individual from developing enough to say – or indicate – “I am not a baby,” you have killed a baby. 
3. I hold it as obvious that a woman has total refusal rights over what becomes of her ova, and a man has the same rights over his sperm.  However once there is a baby, then everybody in the world has a stake in what happens, and a vital stake: no babies, no humans. 
4. Maybe an easy place to start is incest.  Nobody likes incest.  Bateson showed that in quail the birds are less attracted to near kin and to “unrelated” birds they grew up with.  Incest produces reduced fertility – kills babies – and does some other unpleasant things.  So what is the mechanism? 
5. The usual explanation is that the genes that perform so many functions can be damage by a mutation that shuts the gene down.  Since there are 22 pairs of chromosomes (ignoring sex chromosomes), one from each parent, that hold the genes as well as much else. Two ruined genes in the same individual are very bad indeed. 
6. In a small population, with closely related couples, two ruined genes are more likely (than in a large population) to get together and produce a bad outcome. 
7. This accumulates over multiple generations until the line dies out. 
8. Points five and six are a distraction that keep you from looking closely at point seven.  So let us do just that. 
9. Imagine a population of just 4, 2 males and 2 females.  Each of the 4 chromosomes held by the males can be matched at random with any of the 4 held by females.  You get one of each kind of chromosome from each pattern, the other being discarded.  So the possibilities are:                
10.                   Females     

                  Males

Everybody gets two good chromosomes. 
11.Now we assume there are 2 bad chromosomes, one among the males and one among the females.  These can be eliminated either at random by genetic drift or non-randomly by selection:
Females     

                  Males

Starting with
genetic drift, each generation for every chromosome that is passed on, one is eliminated at random; it’s more complicated, but let’s go with the simplification.  Ignoring for now the effects of the chromosomes, each bad one has a fifty/fifty chance of not being eliminated.  That means one of the two in the first generation and the other with a fifty/fifty chance each generation gets eliminated after 2 more generations on average for a total of three generations. 
12. Now look at a population twice as big, four females and four males with eight chromosomes and 4 bad mutations total. 
Females

Males

             
G  (Sorry the grid doesn’t come down this far.)
So now we have four bad genes to get rid of at 50% each.  It’s going to take longer; half are eliminated in the first generation, leaving two, and you have two left, which again will take 3 generations for a total of 4 generations.
13. This is called genetic drift.  A small population will purge itself of a rare mutation faster than will a large one.  So much for genetic drift making incest such a bad thing.   
14. But the question was what happens to bad genes that is due to their (lack of) function.

Looking at the small population again we have:

                                              Females     

                  Males

The X indicates a non-viable baby. We hold the population constant.  Working down from the bad chromosome from the female, there is a one in four chance of matching the bad male chromosome.  That takes on average 4 generations. 
15.  After 4 generations, and holding the population size constant, the population looks like this:

                 Females     

                  Males

We are happy. 
16.  Now we do the same thing with the larger population: Females

Males

             
G  (There it is again.)
17. The female bad gene in red has 2 chances out of 8 of matching a bad male gene, which is a one in four chance and it should take 4 generations to remove this pair of bad genes and the same for the other pair for a total of 2 generations to remove a pair of bad genes.  But, except in the unlikely event of getting two matches at the same time, we are left with two more bad genes.  Females

Males

             
G 
18. The remaining female bad gene will have a one in 8 chance of matching the bad male gene.  That will take another 8 generations.  So on average it will take 10 generations to remove the bad genes from the large population compared with 4 for the small population.  Given that the mutation rate per individual is identical in the two populations, it is the smaller population that does the better job of dealing with bad mutations, whether by genetic drift or by selection against those mutations. 
19. There are many complicating factors and differences from the classical pattern, but the bottom line is clear.  The idea that bad mutations accumulate in small populations is just not true. 
20. That is not to say incest is not bad.  It’s real.  It kills babies.  But the mechanism simply is not genes.  It will take a long time, but I hope some day to lay out the mechanism for you. 
21. Don’t think, “Oh I’m not worried about inbreeding.  We just avoid it.” But if you don’t know the mechanism you are in no position to avoid the same process.  My mother’s attitude was always, “It’s Ok to be scared.  It’s Ok to run away.  Never run scared.”  They say that one way lions hunt is for a female to get a male to hide in the grass.  She then finds a juicy antelope and approaches it just enough to be annoying.  The antelope edges away and thus is herded toward the male.  The male gets worried about all those hooves and horns and eventually stands up and roars.  The antelope bolts only to be pulled down by the lioness. 
If I might: Never run scared; always think scared.
22. And you must understand the mechanism by which incest kills babies or you have no better chance than the antelope of avoiding it.