My sister and I, you will recollect, were twins, and you know how subtle are the links which bind two souls which are so closely allied.
So all life is a great chain, the nature of which is known whenever we are shown a link of it.
As Cuvier could correctly describe a whole animal by the contemplation of a single bone, so the observer who has thoroughly understood one link in a series of incidents should be able to accurately state all the other ones, both before and after.