At the turn of the 20th century, life expectancy at birth in most of today’s developed nations ranged between 45 and 50 years, with women routinely outliving men. About 22% of all individuals born in 1900 in the United States died before reaching the age of 10 years, mostly from infectious diseases.1 Among those who survived into older ages in 1900, the common diseases of aging known today were present but less common.