February 28, 2014

Hans Rosling
Stifelsen Gapminder
Box 38035
100 64 Stockholm

Dear Dr. Rosling:
I enjoyed your presentation “Don’t Panic” at the gapminder site.  I was introduced to the site years ago by my wonderful younger brother.  I am happy to say that the legibility has improved a great deal recently.  Thank you.  My brother regards what I am about to say as “odious.”  You may agree, and I would not blame either, but I say there is no such thing as an odious fact – only odious intention.  The intent to deny crucial information to someone who must make an important decision is high on my odiousness list.  Hence the fact that I have placed the balance of my life into getting the truth out.  Hence this letter.

Your talk, “Don’t Panic,” in which you spell out how world demographics seems likely to play out is full of light and hope.  Your intent and your expertise are of the highest order.  But there is a fact that is lamentable.  It is possible that you do not know it.  It’s about fertility.  The party line is that when a healthy sperm from a healthy man meets a healthy ovum of a healthy woman there is a chance of a pregnancy and ultimately a taxpayer.  If no pregnancy results after many tries, there has to be something wrong with one of the couple or maybe both.

Alas, that is not true, not in the long run.  It matters which man and which woman, and that matters literally as much as the event of the possibility of a zygote.  I recommend my latest summary of my life’s work:
If you look it over I think you will see that there is a fertility price paid when one marries out past second cousin.  Reproductive success, grandchildren, is optimal at third cousin, maybe fourth since their reckoning of “cousin” is not exactly the standard one; that study was done in Iceland, where everyone is assured a good chance at life, so economic factors are not operative.  Indeed the 90% error bars are so tight that there is no room for any other significant factor.  And the study from Denmark found that once issues of kinship were accounted for (the distance between birth places of parent and the size of the town where they lived) there was no effect of education or income on fertility at all.  In other words, since the biology has to be the same, the salubrious effect of education on family size in developing countries is due to the fact that children are meeting children from outside their own circle of kin and nothing else.  Do not think for an instant that I do not applaud the work of distributing birth control material to people who cannot afford more children, which you so touchingly portray.  There are far worse ways to limit family size than the methods illustrated.  But no, it does not seem plausible that in the long run it is really reducing population growth.  Maybe, maybe.  Let’s not go to the mat on that one.  The problem is places like Sweden that are taking the long walk.

Speaking of Sweden, there is also a reference to a study done in England using Swedish data.  They compare wealth with fertility.  They show a decline in fertility that is the same for two generations.  Taking wealth as a surrogate for not being stuck choosing a cousin from the neighbors in the village, the data seem to match exquisitely the Iceland data.  I confess that I have a statistical question.  Should not the infertility outlined in the Iceland study accumulate?  At all events the Swedish data went farther and looked at the great grandchildren.  I find the graphs rather difficult, but it seems that the loss of fertility in the third generation is greater than that in the first two combined.  They had data from the great great grandchildren generation, but they refused to present it.  I think it was probably too scary. 

I’ve shown the effect in fruit flies.  My research partner and I did it because such knowledge might help in malaria control.  The biology does not seem to be exactly the same.  In fruit flies there appears to be a post-zygotic mechanism while in humans (and mice) there appear to be both pre-zygotic and post-zygotic effects.  Thus fruit flies are able to have population cycles, while in mammals there appears to be a first cycle, often a recovery, and then extinction.  The recovery of course must occur only if a single population is considered.  If you keep adding outsiders then the gene pool never is reduced and recovery is impossible. 

When my dear brother introduced me to gapminder, the first thing I did was graph fertility against age at first marriage and follow the course of countries over the years.  When you try it you will see that for a time age of marriage and to a greater extent fertility bounce around for many years.  Then there is a decisive fall in fertility.  Just about as that value falls below replacement there is an abrupt rise in age at first marriage.  There are some exceptions.  In Sweden there is a temporary fall in age at first marriage but then it goes up.  An earlier version of the site did not seem to do that.

At all events this is what you would expect of two mechanisms, one of which happens quickly but then saturates.  The other cuts in later but does not saturate.  In fact it appears to accelerate.  There is no evidence I see that suggests that any population is going to stabilize once it is in the condition of the current rich countries.

It is a coincidence that you should be Swedish.  I spent some happy months as a young man in Scania, or Skåne if you prefer.  In fact it was the only time in my life when I felt like I was at home.  The Skonsk are said to be irrepressibly cheerful.  So am I.  I simply don’t get depressed for more than 24 hours.  When I lose loved ones I feel the pain forever, but not depression.  This of course is a jolly good thing, considering where fate has led me.

While among the merry southern Swedes I noticed that some friends of mine, who lived in a brand new development all next each other, were also childhood friends.  They had grown up in the same neighborhood and when they could afford to build new they all built next each other again.  Also it was explained to me that the students in the university were divided into “nations,” from different parts of Sweden.  They socialized with those from the same area.  Education might have been leading them to marry outside their local population, but an attempt had been made to minimize that.  So I learned those many years ago that staying with the local population was highly desirable.  Alas it would be many years before I realized that the key was fertility.

Thank you both for your wonderful statistics site and for your heart raising presentation.  I hope you take an interest in this because it is so important and so unknown.  Also I could certainly use input from somebody who is both a doctor who has made an effort to serve the most needing, as I have, and who is good with statistics, which I am not.  So I am very eager to hear from you.  I plan to post this letter on my web site named above.  If you would rather I did not, then certainly let me know as much.


M. Linton Herbert MD

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