Diet and stature:
I have just looked at a book.  (The Changing Body Roderick Floud et al. Cambridge University Press, Cambridge 2011) with the subtitle “Health, Nutrition, and Human Development in the Western World since 1700)  I cannot claim to have studied it through properly, but I was interested in the assumptions.  They are: The size and shape of the people in a population indicate how well fed they have been, how long they will live and how hard they will be able to work.  How much work they do – within a given technology – determines how much they will produce, including food.  That influences how big the next generation will be and how much technology can advance.  That influences how well fed the next generation will be.  This cycles. 

It is quite logical and consistent, and there is a copious amount of data and careful work displayed in the book.

So of course I have to quibble. 

My argument goes: A horse is big, strong, healthy, line bred (meaning it is close to being inbred) and fertile.  A mule is bigger, stronger, healthier, crossbred (which is an extreme of out bred) and infertile.  I do not see why humans should be much different except in degree.

As we know, there is an optimal amount of kinship for producing maximum fertility.  Departing that optimum carries a penalty in terms of fertility, and an extreme departure can produce an extreme cost. 

So what I would expect when looking at an occupied landscape that has long been stable would be that the population should be mildly inbred.  If it were out bred, fertility would long since have declined and the stability could not have existed.  If the population’s mating strategy is optimized for fertility, then the population would be growing fast, and the situation would not have been stable.  (According to Robin Fox in the Tribal Imagination, this is the usual case where studies have been done.)  If the population was just at the balance point between being too big to enlarge rapidly and too big to sustain itself, I would expect big, strong, healthy people; in the absence of an understanding of the process, I would expect this to be rare.  Much more commonly, since it’s easier to keep count of a small number of people than a large number, I would expect the population to be rather inbred.  They would be short, not terribly strong and maybe not all that healthy.  This I would take to be the norm. 

Now disrupt the society so that the tight mating pattern is broken down.  Things start to happen.  The birth rate rises so that there is a population boom.  People get bigger, stronger and healthier.  Everybody feels good about the change.  Then fertility collapses and they all die out. 

The book makes the point that bigger, stronger people can do more work.  That has not in general been my experience.  The big man is imposing and may get promotions and better pay because he impresses people, but if you look closely, he really is not likely to be doing as much as the smaller men.  I have no numbers.  But women tend to be smaller at any level of nutritional status, and if you care to tell me that a woman cannot be as productive as a man, I think I am not the only one who will growl. 

Of course the bigger man will be eating more so there will be a correlation between stature and diet, but this may be as much due to inheritance as to malnutrition.  Myself I am just about exactly average height for my age.  It never seems that way, because I tend to hang out with very big men.  But that’s what the book says; I’m spot on average.  My ancestors have been well nourished for several generations.  Yet I and my closer relatives have not participated in the contemporary trend toward gigantism. 

The book says one thing that I have often thought.  Famines generally are man made.  We humans are pretty good at managing to get something to eat unless other humans prevent us.  That is true even in this crowded era when the whole world is staggering under the bloated numbers that have been produced by our passage through the baby boom stage, in turn brought on by release from inbreeding, and that in turn brought on by technology – be it the bicycle or jet aircraft – that gives us the broad mating horizon.

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