The International Eugenics Congresses consisted of three scientific meetings held in London, England, in 1912 and at the American Museum of Natural History in New York City, New York, in 1921 and 1932. Leonard Darwin, son of Charles Darwin, Henry Fairfield Osborn, the President of the American Museum of Natural History, and Charles Benedict Davenport, founder of the Eugenics Record Office at Cold Spring Harbor Laboratory in New York City presided over the Congresses. Scientists presented research in genetics and shared ideas for putting eugenics into practice, such as preventing people they considered inferior from reproducing through forced sterilization. The three International Eugenics Congresses increased scientific and public support of the eugenics movement in the early twentieth century, and established organizations to pursue eugenics agendas that contributed to the forced sterilization of hundreds of thousands of people in the US and Nazi Germany.

Leonard Hayflick studied the processes by which cells age during the twentieth and twenty-first centuries in the United States. In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty times before they cannot divide any further. Researchers later found that the cause of the Hayflick Limit is the shortening of telomeres, or portions of DNA at the ends of chromosomes that slowly degrade as cells replicate. Hayflick used his research on normal embryonic cells to develop a vaccine for polio, and from HayflickÕs published directions, scientists developed vaccines for rubella, rabies, adenovirus, measles, chickenpox and shingles.