A namesake — a U.S. economics professor also called Gregory Clark — has caused waves with a theory that says the 18th century U.K. Industrial Revolution was due to heredity creating superior genes.
In those days, he says, disease and poverty kept lower-class families small. But the upper classes had big families that survived. This allowed population quality to improve, to the point where factories could be created and staffed with efficient workers. Unlike say India or China, Britain was not overwhelmed by the Malthusian pressures of uneducated masses.
As a theory it is at least an improvement on the Protestant ethic theory, which confuses results for causes. Protestantism did not create the ethic that led to the progress of the north European societies. The north European people created Protestantism because it matched the progress-creating ethic they already had.