Origin of Species Variorum

fresh-water shells, as Professor Phillips has urged, have remained almost unaltered from the time when they first appeared to the present day; for these shells will have been subjected to less severe competition than the molluscs .. inhabiting the .. more extensive area of the sea with its innumerable inhabitants. Such objections as the above would be fatal to any view which included advance in organisation as a necessary contingent. They would likewise be fatal to my view if Foraminifera, for instance, could be proved to have first come into existence during the Laurentian epoch, or Brachiopods during the Cambrian formation; for in this case, there would not have been time sufficient for the development of these organisms up to the standard which they .. then reached. When once advanced up to any given point, there is no necessity on the theory of natural selection for their further continued progress; though they will, during each successive age, have to be slightly modified, so as to hold their places in relation to the changing conditions of life. All such objections hinge on the question whether we really know how old the world is, and at what periods the various forms of life first appeared; and this may be disputed.

The problem whether organisation on the whole has advanced is in many ways excessively intricate. The geological record, at all times imperfect, does not extend far enough back, as I believe, to show with unmistakeable clearness that within the known history of the world organisation has largely advanced. Even at the present day, looking to members of the same class, naturalists are not unanimous which forms are to be ranked as highest: thus, some look at the selaceans or sharks, from their approach in some important points of structure to reptiles, as the highest fish; others look at the teleosteans as the highest. The ganoids stand in- termediate