On the whole, scientists do their most creative work before age forty, a tendency that has been taken to show that aging carries with it a loss of creative capacity. An alternative explanation is that by age forty most scientists have worked in their field for fifteen or more years and that by then they have exhausted the opportunity for creative work in that field. Supporting this explanation is the finding that __.
a disproportionately large number of the scientists who produce highly creative work beyond age forty entered their field at an older age than is common most logically completes the passage.