How geography shapes human connection
We are all the product of successful connections — 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 local marriageable pool — what population genetics calls the effective population — is determined by the marriage horizon: how far a person could realistically travel to find a partner. Before turnpike roads, that horizon was 10–15 miles. 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 are of marriageable age. Change any one and the ceiling shifts; change the underlying technology of movement and all three shift together.