May 19, 2014

Stewart Friedman
Wharton Business School
University of Pennsylvania
2208 SH-DH
3620 Locust Walk
Philadelphia, PA 19104

Dear Professor Friedman:

A friend steered me to Baby Bust (Stewart D. Friedman, Wharton Digital Press 2013) and I much enjoyed it, filled as it is with light and hope.  The subject introduced by the title is a worrying one.  UN numbers show that it has been a generation since the developed world was able to produce enough babies to survive, so it is not a self-fixing problem.  You do a heroic job of relating fecundity to economics, the environment, health care, the military and more.  Since all of these are variable and all are related, it makes sense to see how they might be tweaked to provide an outcome we can live with.

I take it as axiomatic that the most human thing about humans is our decisions.  I am for freedom because I like it, of course, but that is not whim.  Denying freedom limits choices and dehumanizes.  Your quest in seeking the right decision is thus an ultimate human expression, and I wholeheartedly praise you.

But there is a third participant in this conversation who is less impressed.  Mother Nature doesn’t care, and as age advances I am ever more aware that Mother Nature gives orders you jolly well need to heed.  The natural law is that there is just one thing (barring rare medical conditions) that determines the fertility of a healthy couple, and it is unrelated to any of the other factors.  We can’t just make things we the way we would like.  (Remember the cruelty joke: “Mummy, mummy, why do I keep walking in circles?”  “Shut up or I nail your other foot to the floor.”)

Fertility depends on consanguinity – the kinship of your parents, their parents and so forth.  There are a couple of papers (Human Fertility Increases with marital radius. Rodrigo Labouriau and António Amorim.  GENETICS volume 178 January 2008 page 603 and 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) done in Denmark.  According to their exemplary data once issues of consanguinity (as estimated by them from the distance between the birth places of a couple and from the size of the town they lived in) were accounted for, there was absolutely no effect of education or income on family size.  The awkwardness of that sentence reflects the awkwardness of the fact, but read it again and let it sink in.

This is no fluke.  Anther paper (An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 – 816) found exactly the same relationship in Iceland, this time based on actual genealogy; their error bars are so tight that there is no room for any significant economic or social effect on fecundity.  A collection of nigh two thousand papers regarding field counts of animals (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) found precisely the same relationship; the other factors that tie in with fertility in humans are irrelevant to wild animals. 

So of the interrelated factors, fertility is always cause, never effect.  Nature has nailed that foot to the floor.  You can annoy yourself with my lengthy ramblings on the issue at, but those four papers make the point with overkill. 

The freedom to choose means the freedom to make mistakes.  I’ll stand by anybody’s right to get things wrong.  But a choice made in ignorance is not a free choice.  People have an absolute right to the truth relevant to their decisions, and if I were to say there was some supreme requirement for humans it would be that they would be at least exposed to some rudimentary clue regarding the best estimate of the truth.  But the overwhelming majority is denied it.

To ramble a bit, I find the silence eerie.  It is as if we had gone so far down the road of outbreeding that Nature has fixed in out brains that babies are a bad idea; She has marked us for elimination.  Nobody minds.  Your book proves you are a blessed exception. 

Let me know what you think.


M. Linton Herbert MD

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