 All modern Balwen sheep are therefore presumably descended from this one ram, although it is possible that some of the ewes may have been in lamb to rams that did not survive the winter.Outcrossing with other types of Welsh Mountain sheep may also have occurred, and this would have increased the genetic diversity of the breed.During the 1950s and 1960s a steady increase took place, and in the 1970s people outside the valley began to take an interest in the breed.