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I spent 2 months as a diagnostic radiologist for Project Hope in Jamaica in 1973 and dearly loved the island.  Who wouldn’t?  I’m sure much has changed since those days. 

My interest is in kinship and fertility.  The short version is that in the old times we all married cousins and there were lots of babies; now we almost never marry cousins, and there are few babies.  The long version is too long to go into here, but if you want it, my best effort so far is at
but I’ll try to be more brief.

First, congratulations are in order.  I see that the birth rate in Jamaica is just about perfect for a long term stable population.  Most countries nowadays are either in freefall or are meta-stable at below replacement.  Obviously a rate below replacement cannot be stable, and things are actually more pressing than one would think.

What has been happening is that for country after country the birth rate falls and than stops falling as I said below replacement and just as that moment is reached, the age at first marriage starts to go up.  Once it has started going up it just about never stops and goes back down again.   (I would say that you can verify what I am saying by going to, however it seems that, literally within the past hour the site is down.  I hope they are adding more data and not simply going dark.) Jamaica has the highest age at first marriage of any country save Martinique, and while Martinique has a birth rate below replacement, Jamaica’s is still all right in that regard.

But there is a cloud on the horizon, now no larger than a man’s hand.  The age at first marriage for women in Jamaica is still rising.  Compare that with the same number in Sweden (I remember when Swedish matches were popular; are they still?) and you will see that the age in question in Sweden is rising faster, although as of 2005 the age was still lower. 

We think of age at marriage as being choice, but that is a new notion.  We used to refer to a “biological clock.”  When a young woman started to act a bit strangely, we’d say, “Her biological clock is ticking,” by which we meant she is going to get married soon so get with the program or get out of the way.  Well those clocks are stopping all over the world, and alas this time Jamaica is not spared.

As age of marriage rises, there is no obvious limit other than life expectancy, but something is going to happen as the age passes 40.  If the age is, say, 32 then babies are appearing over an eight year span thereafter and pretty much a symmetrical eight year span before that; few will be born of women under 24.  And when average age of marriage reaches 36 few will marry before 32.  In Sweden the age of marriage rises about one year for each 3 calendar years.  That means, as of the most recent statistics on gapminder, the bottom of the range is coming up a year every 18 months.  That is fast indeed.  Top bottom and 40 are all going to reach each other in a flash. 

I’d say Jamaica needs to get those clocks running again.  Alas I am not in a position to say how.  Nobody has ever tried it, so this is research not advice.  You can get an authoritative write up from Chapter 19 “Marry in or Die out,” in the textbook Handbook on Evolution and Society published this year.  But before advice can be given, more research needs to be done.  I would say that one promising line of research, paralleling work done in Iceland as described in the link I gave and more clearly in that Chapter 19, would be to have a study of third cousin marriages.  Offer them something generous to join the study if, cupid directing, third cousin couples marry.  After a few years you will know whether what is suggested in Iceland also works in Jamaica.  And you will be prepared better than anyone in the world when, as there is reason to suspect, the curtain falls on Sweden.

By the way, this has nothing to do with race, nationality, ethnic group or anything else on a large scale.  Tenth cousin is the same as the far side of the world.  It’s all about family, and when I was there family was important in Jamaica. 

Let me know what you think.


M. Linton Herbert MD  
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