It may also be objected that if, as held by some evolutionists, man was slowly developed from lower animals, and if his earliest known remains are still human in their characters, he must have had a vastly longer history covering the periods of his gradual change from, say, ape-like forms. This is admitted; but then we have as yet no good evidence that man was so developed, and no remains of intermediate forms are yet known to science. Even should some animal, either recent or fossil, be discovered intermediate in structure between man and the highest apes, we should still require proof that it was the ancestor of man, by the occurrence of connecting forms, or otherwise. As the facts now stand, the earliest known remains of man are _still human_, and tell us nothing as to previous stages of development. We must now glance a little more particularly at what may be termed the more immediate antecedents of man. The latest great period of the earth's geological history (the cenozoic) was ingeniously subdivided by Lyell, on the ground of the percentages of extinct and surviving species of marine shells contained in its several beds. According to this method, which, with some modifications in detail, is still accepted, the eocene age, or that of the dawn of the recent, includes those formations in which the percentage of modern or still living species of marine animals does not exceed three and a half, all the other species found being extinct. The miocene (less recent) includes beds in which the percentage of living species does not exceed thirty-five. The pliocene (more recent) includes beds in which the living forms of marine life exceed thirty-five per cent, but there is still a considerable proportion of extinct species. Newer than this we have the pleistocene (most recent), in which there are scarcely as many extinct species as there are of recent in the eocene. Lastly, the modern, of course, includes only the living species of the modern seas. Other geologists, notably Dawkins and Gandry, have arrived at similar results from a consideration of the vertebrate animals of the land. In the eocene we find numerous remains of mammals, or ordinary land quadrupeds, but all are extinct, and nearly all belong to extinct genera. In the miocene there are many living genera, but no species that survive to the present time. The pliocene begins to show a few living species, and these are dominant in the succeeding pleistocene.