September 7, 2012
to be posted on

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

Dear Anna Goodman:
I read with enormous interest of your work as published in ECONOMIST.  (More or Less ECONOMIST vol. 404 no. 8800 September 1, 2012 page)  In my enthusiasm I sent a letter to that magazine as fan mail.  I attach it.  They are most unlikely to publish it.

The demographic transition is the observation that when a society gets rich, fertility falls.  Received wisdom is that richer people are investing more in their children but having fewer.  The result ought to be an increase in the number of grandchildren.  What you have found is that this is not the case.  Within a rich society such as Sweden the children of rich people do indeed prosper in many ways but their fertility is so low that they do not make up in grandchildren the number that would be expected for the grandchildren of poorer people.  Superficially this makes no sense from an evolutionary standpoint.  Things get worse as you follow succeeding generations; fertility continues to fall.  And fertility in Sweden on average, for the Swedish born, is already below replacement.  The article does a little hand waving and suggests that psychological factors that may have been present in earlier times are not appropriate now.  I find it hard to imagine how the survival of a population was ever encouraged by a birth rate below replacement.  On the face of it, nature is simply eliminating the offspring of the rich from among us. 

Since the process accumulates over generations, it cannot be due to some sort of gene mixing, which would be a one off event.  Nor can it be due to genetic mutations; it is far too fast for that.  It must be epigenetic.  There must be a mechanism that has evolved that specifically brings down certain populations in response to some sort of clue.

The obvious clue would be consanguinity.  We used to marry cousins and there were lots of babies.  We now almost never marry cousins and the babies have gone away.  It would be a simple matter for evolution to produce a mechanism for checking consanguinity; if it is too low, so shall fertility be too low.

What seems glaringly obvious once one considers it is that this mechanism simply had to evolve.  Consider that evolution takes about 2,000 generations.  I shall not quibble about the number, but if you wish to choose 10,000 generations we shall have to look at some evidence.  Split a population and establish reproductive isolation for 2,000 generations.  Some key chromosome in one population if now matched with its homologue in the other cannot function in a way that causes normal growth and development.  There will be hybrid infertility.

Now consider a population of 1,000.  Those same two chromosomes will now be separated, more or less, for 2,000 generations on average before they find themselves in the same zygote.  In the fullness of time the population must die.  Since there are many species that have not died, evolution appears to have worked out two kinds of solution.  There are immediate factors that keep random mating throughout the population from happening.  Territoriality comes to mind.  If such measures fail, then there is a backup.  Some epigenetic process then must be checking gene pool size, and if that gene pool size becomes and remains too large, the population is simply eliminated.  Otherwise the whole species would die; two thousand generations is a long time and it is unlikely that different communities in the species would remain isolated from each other for that long.  The epigenetic process must work faster.  In fact it appears to take it about 10 generations to lay a population low.  That of course is what you would expect if all populations of something like 1,000 were to be eliminated.  2 to the tenth is pretty close to 1,000.

There is evidence that this has happened many times in the past.   This is not just feverish extrapolation from some recent statistics.  At the same web site you can see studies showing the effect of outbreeding depression in human populations, specifically Denmark and Iceland.  (What is it about Vikings?) 

There is an argument that rich people are parasites on the community as a whole, consuming more than their share of resources while not working much harder than the rest of us.  But rich people, and I mean those with a college education, do provide a service.  It is they who make it possible to maintain a high tech civilization.  Most demanding work tends to run in families, if your father is a glassblower or an engineer, you will have a head start on someone whose father was quite unskilled.  So a collapse of the population that now includes the rich will most likely carry away our high tech civilization.  That will leave a world of some ten billion people for a short while with the technology that can feed two billion under the best of circumstances, and harvest will be far from the best not to mention the distribution system.  This would be an event I think anyone would like to avoid. 

If you have any question, please do let me know.


M. Linton Herbert MD 
Note: Anna Goodman was kind enough to acknowledge receiving the letter. 

There have been 67,333 visitors so far.

Home page