"The third [and last key] element in the decline of disease and death was better nutrition.  This owed much to increases in food supply, even more to better, faster transport.  Famines, often the product of local shortages, became rarer; diet grew more varied and richer in animal protein.  These changes translated among other things into taller, stronger physiques.  This was a much slower process than those medical and hygienic gains that could be instituted from above, in large part because it depended on habit and taste as well as income.  As late as World War I, the Turks who fought the British expeditionary force at Gallipoli were struck by the difference in height between the steak-and-mutton-fed troops from Australia and New Zealand, and the stunted youth of British mill towns.  And anyone who follows immigrant populations from poor countries into rich will note that the children are taller and better knit than their parents. ...