I'm writing in response to this post:

>Has anyone seen the cover article of the October 14 Time (this is the cover
>article of the international edition, probably not the american). Its a
>fascinating article "A Tall Story of Our Time" about the science of
>auxologists (they study average hight of ppl over history, and possible
>causes for changes) they state that all over the world ppl are getting
>taller and that this is an excellent measure of health of the population.
>The reason I'm writing to you all about this is the glaring LACK of any
>mention of breastfeeding as a factor. The article explains that humans have
>two growth spurts, at infancy to age 2 and at adoloescence. They talk
>extensively about how nutrition is a factor, as well as love and nurturing.
>Well we know the best nutrition during that first growth spurt! They discuss
>how the Spanish and Portuguese are shorter (didn't someone just post how the
>BF rate there is abismal) and that the tallest ppl in the world are the
>Dutch (isn't their BF rate really high?) They come so close to mentioning or
>at least asking about BF as a factor of nutrition that effects average hight
>But they just don't do it. Seems like a glaring omition to me!! Who do we
>write to??? Author is Rod Usher.


As most of you know, I am a specialist in infant/child feeding and growth,
so this is right up my alley, as it were.  "Auxologists" are people who
study growth and development, not necessarily those who study average height
of people over history.  I'm an auxologist.  All that means is that I study
growth and development.

The trend toward populations getting taller and taller over the last few
decades/centuries is called "positive secular trend for height."  Not only
are adults getting taller, but children are getting taller younger.  Girls
are also going through puberty earlier and therefore having their first
menstrual periods earlier.  The causes of these positive secular trends are
thought to be twofold: better diet and better health care/fewer diseases.
There is probably not any increase in genetic potential, but rather more and
more individuals are meeting their genetic potential through access to
better food and health care or fewer diseases through immunizations,
antibiotics, and better sanitation.  *Breastfeeding isn't mentioned because
it probably plays no role.*  We all know (don't we?) that bottle-fed
children may, on average, grow faster during the early years, so
bottle-feeding may contribute to positive secular trend in some populations.
Once you have maxed out your genetic potential, changes in diet/health
aren't going to make any difference, as you can't grow more than your
genetic potential.  Populations that have had the greatest improvements in
diet in terms of lots of protein (esp. meat) and plenty of calories have
also had the greatest improvement in health care (immunizations, antibiotics
and sanitation) AND they are also the ones most likely to be bottle-feeding,
because these are the Western industrialized nations.  If anything,
bottle-feeding contributes to populations growing taller at an earlier age
and going through puberty earlier.  These are not necessarily good things!

If you look at differences in growth patterns and final adult height in
populations from around the world, you find that wherever populations have
adequate diets and good health care/freedom from diseases, that everyone
ends up with an average height for males of around 5'6" to 5'8", and females
of around 5'3" to 5'6".  In the U.S. the average height for modern males is
about 5'8" and the average for modern females is 5'6".  If you look at
populations that are typically stereotyped as being genetically short, such
as the Maya of Guatemala or the Vietnamese of Viet Nam, you find that when
they move to the U.S. and start eating more food with higher protein
content, and having fewer diseases to deal with and a less stressful
environment (no warfare), that they grow just like American kids and end up
at the 5'6" and 5'3" averages.  Not *quite* as tall as typical Americans,
but MUCH taller than their counterparts who stayed at home.  And it may very
likely be that with another generation or two in the U.S., that 2" height
difference will also be erased, as the effects of childhood malnutrition can
pass on from one generation to the next.  And remember that individual
members of the population will be much taller.  We have a football player
here at A&M whose is Vietnamese (both parents born and raised in Vietnam)
and he is 6'1" tall and weighs 213 pounds.

Also, remember that there has been natural selection for specific body
shapes/sizes over the generations of human evolution, such that populations
that live where it is hot and arid tend to have body shapes/sizes that
maximize surface area to volume.  So some tend to be tall and have a linear
shape (such as Manute Bol, the basketball player from the Sudan who is 7'6"
and has an arm span of 8'0") and populations that live where it is cold tend
to have body shapes/sizes that minimize surface area to volume, so you get
either short and stocky, or just "big all over" body configurations like the
Dutch.

So, don't be too harsh on the authors of the TIME International article for
not mentioning breastfeeding, as the impact of breastfeeding would probably
be to counter the effects of better diet and health care in producing
positive secular trend.

There are signs that Americans have maxed out their genetic potential, and
we won't be seeing any more increases in average adult height, nor any more
decreases in age at menarche (first menstrual period) below the current
average of about 12 years for US females.


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Katherine A. Dettwyler, Ph.D.                         email: [log in to unmask]
Anthropology Department                               phone: (409) 845-5256
Texas A&M University                                    fax: (409) 845-4070
College Station, TX  77843-4352