August 25, 2010

Mariette DiChristina
Editor in Chief
Scientific American
415 Madison Avenue
New York, NY 10017-1111

Dear Mariette DiChristina:
I found your doom and gloom issue fascinating and instructive.  Thank you.  You did miss a couple of my favorites.  One is the abrupt onset of an ice age.  I would rate that at something about 6 on your scale,  the equivalent of a nuclear exchange, killing hundreds of millions but not billions.  I would give it a time scale of about 10 years and a likelihood of some 1 in 10.  But I cannot think of anything to do about it (and I can’t cite articles, so it would not have done you any good to consider it). 

More to the point is the question of babies.  The world will reach peak coal and oil production in the foreseeable future as your issue expertly points out.  It will also reach peak baby production.  Nobody much talks about that, but it has to happen before peak population some time about mid century.  This time I can cite the literature.

In humans, as in other animals, fertility is related to the kinship of a couple and of their ancestors.  (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 no. 309 July 22, 2005 page 607, An Association Between Kinship and Fertility in Human Couples, Agnar Helgason, Snaebjörn Pálsson, Daniel Guöbjartson, Pórdöur Kristjánsson and Kári Stefánson, SCIENCE vol. 319 no. 319 February 8, 2008 page 813, Human Fertility Increases with Marital Radius, Rodrigo Labouriau and António Amorim GENETICS vol. 178 no. 1 January 2008 page 601 and Comment on “An Association between Kinship and Fertility of Human Couples”, Rodrigo Labouriau and António Amorim SCIENCE vol. 322 no. 5908 December 12, 2008 page 1634)  It is always the same story.  Malthus was wrong.  Populations do not increase exponentially and indefinitely.  Infertility supervenes. 

The earlier Labouriau study specifically address the question of whether fertility is a matter of choice and concludes that it is not.  Evidently as the world has become richer, freer and more mobile people have mated outside the tight circle that is biologically viable. 

This would not rank as a species ender, 9 on your scale, but just a notch short.  Call it an 8.  There would still be a few groups such as those described in “Last of Their Kind” by Wade Davis in the September issue, small groups outside the global reach of increasing genetic diversity.  A better title might be, “Last of Our Kind.” 

Unlike the notion of a returned ice age, this time there is plenty we can do about it.  Or could have done about it had we started a couple of generations ago.  It may now be too late.  Call it a fifty-fifty chance of preserving civilization.  The time scale looks to be about 100 years, maybe only 40 or 50, but it is to be hoped longer.

On the bright side, I can promise that the extinction of the human species will not happen during your lifetime.  (But it could happen at the end.)

All the best, and thanks for an issue that is zany, touching, scary, serious and well done.


M. Linton Herbert MD

If you hunger for more evidence, I pile it up along with my correspondence and some related material at

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