October 18, 2012
to be posted on nobabies.net

Anna Goodman
London School of Hygiene and Tropical Medicine
Keppel Street
London WC1E 7HT
Phone (+44) 202 7958 8382

Dear Anna Goodman:
Forgive the temerity of writing you again, but I am overcome with enthusiasm.  The ECONOMIST review did not do you justice.  (And I see you also got a plug in SCIENCE.  I have now bought a copy of your paper from Proceedings of the Royal Society B (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).

You said (and for my readers, “high SEP” basically means “rich”):  By contrast if both early- and late-child-bearing lineages have similar total fertility (as was the case in our study for high SEP and low SEP lineages), and if the population as a whole has below-replacement fertility (which currently applies to more than half the world’s population [8]), then shorter generation time may simply speed up a lineage’s trajectory towards extinction.” 

To paraphrase the old constable in Young Frankenstein, “Panic is an ugly thing … but I think it may be time for a good old fashioned panic.”  (Actually I have never known people to panic.  Governments panic.)

In other words you point out that the number of children a couple can expect is not real related to when they have those children.  That is in keeping with what I seem to find, which is that fertility depends on exactly who marries whom and some factor that is hardwired into each at birth. 

However I would beg to take issue in this particular case.  (I am quite mindful of the fact that in discussing statistics with you it is a case of Bambi meets Godzilla.)  As advertised, your statistics show that first generation appears in your first graph and is nicely summarized in your figure 4, declining fertility with increasing SEP.  This continues in the second generation, with the number of grandchildren again below that of those with a lower SEP.  And with great grandchildren it gets worse – a lot worse.  A reasonable and prudent mind would expect that any effect should have begun to fade by then.  Of course as you point out, high SEP families have the resources (and I suspect the home environment) that tend to produce high SEP children.  But it isn’t air tight.  And by great grandchildren there ought to be some sort of diminution; else upward social mobility is a myth.  But you also have numbers of the next generation, the great great grandchildren.  I suspect things are worse than they appear.  As you properly point out, it is hazardous to say how many children a population is going to have until they are done.  But it is my understanding that the age of first baby for women has been going steadily upward for women in Sweden.  In other words, that fourth generation manages to do as well as it does, which is very badly for those with high SEP ancestors, by having women bear their children at ever greater ages.  That can only go so far.  If I could come up with a suitable wager (and could promise to live that long) I would bet that the next five years show a precipitous decline in the birth rate for the high SEP descendants. 

So what is causing all this?  I think you know.  You say, “Firstly, we do not have access to information on the genetic basis of the traits we examine.”  Yes, you are absolutely right.  It’s genetic.  Or rather it’s epigenetic.  Here are some references:
On the Regulation of Populations of Mammals, Birds, Fish and Insects, Richard M. Sibly, Daniel Barker, Michael C. Denham, Jim Hope and Mark Pagel SCIENCE vol. 309 July 22, 2005 page 609

An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 – 816

Human Fertility Increases with marital radius. Rodrigo Labourian and Antonio 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

They speak with a single voice: consanguinity dictates fertility.  Humans, animals, it’s all the same.  Your high SEP folks had a broad social horizon and married by and large people less kin than fifth cousins and did so at a far greater rate than those of more modest SEP.  They broke the Great Law: MARRY KIN.  It is sobering to see the words “visiting the iniquities of the fathers upon the sons, even to the third and fourth generation” laid out in clear state of the art statistics.

Thank you for your interest in this vitally important matter. 


M. Linton Herbert MD 

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