Joel Mokyr on living standards during the Industrial Revolution

One of the notable arithmetical truths about the period of the Industrial Revolution is that it is quite possible (if not certain) that biological living standards in both urban and rural areas rose and yet average living standards declined.  This can happen if urban living conditions are significantly worse than rural ones, and the proportion of people living in cities is rising because of migration from the countryside to the towns.  It seems likely that the biological measures of living standards were especially sensitive to urbanization.  While urban areas may have offered some positive amenities (such as entertainment and more choice in shopping), healthy living conditions were surely not among them.

That is from Mokyr's new and notable The Enlightened Economy: An Economic History of Britain 1700-1850.  The obvious question of course is why so many people moved into cities.  Did "new goods" make the urban living standard higher than some measures might suggest?  Was it to avoid boredom?  To avoid "rural idiocy" and invest in future IQ externalities for children?

Here is my previous post on the book.