Investigating the weird and wonderful world of identical twins, the first in a special two-part series looks at what science can learn from the uncanny similarities between twins.

Two hundred and fifty pairs of twins gather at St Thomas' Hospital to celebrate their contribution to science, while identical twin doctors Chris and Xand Van Tulleken set out to discover if their shared genes mean they will forever be identical. Meet twins raised apart as they're finally reunited, twins who suffer identical illnesses at the same time, and find out how identical twins hold the key to understanding what makes us all who we are. Show less