Big population pitfall:
It has been rather standard to attribute technologic progress to increasing population size.  That seems to make sense on the face of it.  With more people there will be more ideas and more opportunities for ideas to get swapped around.  But it always made me squirm.  Over a period of years the logic that progress is enhanced by greater numbers makes good sense.  But over a period of generations the bigger population is more vulnerable to collapse because of outbreeding depression, and when it collapses it takes any progress with it. 

Now the blessing of great population has been questioned.  (Shells show rise of Homo sapiens NATURE vol. 498 no. 7455 June 27, 2013 page 410 reviewing Proc. Natl Acad. Sci. USA (2013)) 

Teresa Steele at the University of California, Davis and Richard Klein of Stamford University, California looked at ancient limpet shells. 

Limpets are 2 to 10 centimeters across and shaped like pointed hats.  At night they graze on algae and during the day return to their favorite spot and hunker down.  They live in tidal pools.  For a human they are a tasty treat just waiting to be pried up.  As it turned out, limpet shells from Middle Stone age, from 50,000 to 200,000 years ago were bigger than later shells.  The inference is that bigger shells means fewer people around.  The creation of symbolic artifacts in that area dates back to about 100,000 years ago.  So the sequence appears to have been cognitive progress followed by population growth, just as one would expect under conditions where dense populations are in peril of extinction, rather than the reverse. 

One robin does not a spring make, but it makes excellent sense to me.  I shall hasten to try to get a message through to Teresa Steele in case she is interested.       

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