"It seemed obvious to [Darwin] that, if his theory of evolution [were] correct, fossils ought to provide incontrovertible proof of it, since each stratum should contain links between the species of earlier and later strata, and if sufficient fossils were collected, it would be possible to arrange them in ancestor descendent sequences and so build up a precise picture of the course of evolution. This was not so in Darwin’s time, and today, after more than another hundred years of assiduous fossil collecting, the picture still has extensive gaps."