October 5, 2013
to be posted on nobabies.net
Alan H. Bittles
Murdoch Campus
BITL Buidling
Room 3,006
61 8 9360 6088
Centre for Human Genetics
Edith Cowan University
100 Joondalup Drive
Perth WA 6027
Australia
abittles@ccg.murdoch.edu.au
Dear Professor Bittles:
Your book was recommended to me by Prof. Robin Fox of Rutgers and I have read it with enormous interest. Our styles differ. I find you to be methodical, authoritative, and even handed with encyclopedic interest in your topic. I suppose I might be called an alarmist obsessed with the upper right hand corner of your diagram on page 212 – the relationship between consanguinity and fertility. Although we differ in style I have learned from you and perhaps I can offer something in return.
I’m sure we agree that no population can endure perpetual increase nor perpetual decrease. Finding the balance is survival itself. You cited the Iceland study which shows maximum reproductive success for matches that are the equivalent of third cousin or closer to fourth cousin or closer (emphasis mine). I make that to be third cousins. Of course the way they recon cousins is by going back ten generations and counting shared ancestors. That introduces a slight distortion in the other direction, so I make little of it. But the thing that is striking to me is the tightness of the error bars. At first glance it appears that fertility depends on consanguinity and nothing else (gratuitous emphasis). The bars are two standard deviations. The variability in the number of grandchildren must be almost completely caused by the variability in the number of children. Pursuant of this, there are a couple articles from Denmark (Human Fertility Increases with marital radius. Rodrigo Labouriau and António Amorim. GENETICS volume 178 January 2008 page 603 Comment on “An Association Between the Kinship and Fertility of Human Couples,” Rodrigo Labouriau and António Amorim SCIENCE vol. 322, page 1634b December 12, 2008) that need to be taken together. They show (allowing for a difference in the way kinship is estimated) identical results with the Iceland study; and the Danish study goes on to say that once issues of consanguinity are taken account of, there is no influence on fertility by education or income. In other words there is no choice whatever any more than there is for animals, which also follow exactly the same pattern.
My father used to say, “Son, you have a choice. You can do it happily or you can do it unhappily.” Well we are going to get a handle on consanguinity, and if we don’t do it happily we are certainly going to do it unhappily. Some days I wonder if our very survival as a species is at stake.
I think the critical difference between us is that you focus on the effect of consanguinity on a single generation; I look at multiple generations. The effect – whatever causes it – seems to accumulate over generations. The Iceland study analyses two. I wish they looked at more. There is a study from Sweden, (Low fertility increases descendant socioeconomic position but reduces long-term fitness in a modern post-industrial society Proc. R. Soc. B 2012 279, 4342-4351 first published online 29 August 2012 Anna Goodman, Ilona Koupil and David W. Lawson) and if you take as an axiom that rich Swedes don’t marry cousins, the effect carries, nay is amplified when it comes to great grandchildren. The author declined to look past that or to reply when I wrote her. I fear that in both the Swedish study and the Icelandic study the news down the road was simply scary.
I must thank you for your challenging me on a few points; I so rarely get challenged by data. I had noticed data indicating that those who live in cities get schizophrenia more often than those who live in the country, and the protective effect of country living persists even after a person moved to the city. My reaction was that this result is explained by greater consanguinity in the country. You have data to the contrary.
A second point is that we agree that increased stature is probably due to decreased consanguinity. My own experience has been that the surge in height in my part of the world has been followed by a surge in weight and I posited that the cause was the same. You have data that calls this into question.
The third point is that I follow a blog http://hbdchick.wordpress.com/ that takes a great interest in consanguinity. From time to time “chick” will say something like, “And they have been marrying kin for centuries,” to which I sometimes remark, “Marrying kin is the default setting. People always did. Those that didn’t died out.” Maybe my position is extreme, and it generally does not elicit positive responses, and for the first time there is data that, yes, there can be an increase in first cousin marriages.
If the good fairy were to grant me a third wish (after seeing how great grandchildren do in the Iceland data and great great grandchildren in the Swedish data) I would like to know what the mating strategy is among the Australian Aborigines. They have to be the all time world champions at establishing and maintining a stable population.
My gut feel is that there are five significantly different degrees of consanguinity.
Incest: Not recommended. Of course genetically it should be no big deal. As you point out deleterious recessives get purged so things should get better and better. But there is a study showing that in certain plants (I’ll try to run it down if you like) all inbreeding effects are eliminated if the seeds are raised in a demethylating environment; in other words it’s all epigenetic. My own computer simulation also shows as much.
First cousins or thereabouts: The Icelandic study suggests that there is a degree of average consanguinity where the population should be stable. This would be rather easy to implement but causes a reduction in the size of the social horizon one is altruistic toward.
Third cousins or thereabouts: What Robin Fox would call optimal outbreeding, results in rapid population growth and is unstable.
Seventh cousins or thereabouts: Very difficult to implement but promises long term stability with a maximum sustainable horizon of altruism.
Tenth cousins and beyond: Suicide. They all die out.
It’s only a gut feel, but it looks valid from data you have already looked at.
You mention that people are more likely to be helpful to people who share a name. My name is Linton Herbert, so you can imagine. Were I clever I should have said I was named Alvin Bittles. Nonetheless perhaps you would let me know what you think. My best link for a summary is: http://nobabies.net/A%20December%20summary.html
Sincerely,
M. Linton Herbert
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