Page:Darwinism by Alfred Wallace 1889.djvu/433

 exhibits a steady progression from lower to higher types, excepting only the deficiency in the bird record which is easily explained. The comparative perfection of type in which each of these classes first appears, renders it certain that the origin of each and all of them must be sought much farther back than any records which have yet been discovered. The researches of palaeontologists and embryologists indicate a reptilian origin for birds and mammals, while reptiles and amphibia arose, perhaps independently, from fishes.

The brief review we have now taken of the more suggestive facts presented by the geological succession of organic forms, is sufficient to show that most, if not all, of the supposed difficulties which it presents in the way of evolution, are due either to imperfections in the geological record itself, or to our still very incomplete knowledge of what is really recorded in the earth's crust. We learn, however, that just as discovery progresses, gaps are filled up and difficulties disappear; while, in the case of many individual groups, we have already obtained all the evidence of progressive development that can reasonably be expected. We conclude, therefore, that the geological difficulty has now disappeared; and that this noble science, when properly understood, affords clear and weighty evidence of evolution.