nature's only controlled experiment, run for free by biology since forever.
means research comparing identical twins (same genes) to fraternal twins or separated twins to measure how much of a trait comes from genes versus environment.
from formalized by francis galton in 1875 as a way to weigh nature against nurture, though galton also happened to be darwin's cousin and a founder of eugenics, a shadow the field still has to explain itself out of.
minnesota twin study — 1979 to 1999, 137 pairs raised apart, thomas bouchard led it
jim twins — separated at birth, both named their sons james, both drove chevrolets
swedish twin registry — over 85000 pairs, largest twin database in the world
three identical strangers — 2018 documentary on triplets separated for a psychiatric study