How geography shapes human connection
We are all the product of a successful connection — successful in a simple biological sense. The ancestor tree takes you back to the 1700s. The ‘Tree Meets the Parish’ interactive allows you to see how gene pool, local geography, and changing social, technological, and economic forces interact. The pool of possible partners — the breeding population, in the technical register — is determined by the ‘coupling horizon’: how far a person could realistically travel to find one. Before roads, railways and air travel, that horizon was probably 5–10 miles, with longer journeys rare. The pool is a product of three coupled factors: how many settlements fall within that radius, how large they are, and what fraction of their inhabitants will go on to have children. Change any one and the ceiling shifts; change the underlying technology of movement and all three shift together.