Hi Phil, 
You asked:
> But did all that size reduction occur after the development 
> of agriculture, or did the shrinkage begin before then?

According to Wolfgang Lutz: "It is of great interst that early farmers in
Greece and Turkey were five inches shorter than their atheltic paleolithic
ancestors."(1) 

The source he cites for this claim is Angel (2)

I haven't been able to acquire a copy of Lutz's source. However, there is
congruency with the data from excavations at Abu Hureyra (3). In a report by
Roger Lewin,  Theya Molleson of the British Museum "identifies deformation
os in the legs, feet, and vetebra that indicate the carrying of heavy loads
and the reletless hand-milling of grain." This of course overlooks the
possibility that grain consumption could cause the same injuries to these
bones. 

Later in the same article lewin states: "Cohen has been collating physical
anthropological data that appear to show increasingly pooor nutritional
status conincident with the beginnings of agriculture, indicating, he says,
food stress as an engine of the change." Again, the likely impact of
significantly increased cereal grain consumption would be to cause signs of
food stress, but it is impossible to determine which issue (perhaps both?)
caused the signs that Cohen attributes to "food stress". 

In another article, Roger Lewin explores mitocondrial DNA research by Byran
Sykes, Martin Richards, and their colleagues (4). They have shown that
european populations have remained relatively static. Conventional wisdom
long held that agricultural expansion happened as farming europeans thrived,
reproduced, and the farming population spread out displacing
hunter-gatherers. However, the work by Sykes et. al. suggests that the
expansion was more a spread of farming practice than of the farmers
themselves. 

None of this offers conclusive evidence, of course, but I do find it
interesting. Examination of the modern impact of grain consumption on
diseases of civilization and particularly on integrity of bones offers some
insight.  In American sites, we have genetic evidence of the declining
stature in association with cereal grain (corn) cultivation, although I
can't seem to find that report. Without tbe modern issues of bone density in
the context of gluten sensitivity and celiac disease, the data could be
interpreted either way. However, given the modern data, it seems more likely
that the data have long been misinterpreted because of the underlying
assumption that grains provided a healthful diet. Although agriculture
required more work, the prevailing assumption has been that it was adopted
following development of food shortages and consequent losses in stature.
Although that may have been a factor, available evidence suggests that the
"new" food was a greater cause of bone degeneration.  

Sources:

1. Lutz WJ, The Colonization of Europe and Our Western Diseases.  Medical
Hypotheses. 1995. 45;115-120
2.  Angel L S, Paleodemography and health. In: Polgar S., ed. Population
Ecology and Evolution. Den Haag: Mouton, 1975: 167-190
3. Lewin R.  A Revolution of Ideas in Agricultural Origins. Science 1988:
240; 984-986
4. Lewin R. Ancestral echoes. New Scientist. 1997. July 5; 32-37.  

> 
> I found this source in my files, but it doesn't mention when 
> the shrinkage occurred exactly:
> 
> HISTORY OF STONE AGE MAN
> http://www.historyworld.net/wrldhis/PlainTextHistories.asp?his
> toryid=ab10
Thank you for that very interesting information. 

Best wishes, 
Ron Hoggan, Ed. D.
co-author Dangerous Grains ISBN: 978158333-129-3 www.dangerousgrains.com 
editor: Scott-Free Newsletter www.celiac.com
"Objectivity is the prerogative of objects."