Between the bird carved upon an Egyptian or Assyrian slab, and its representative at the present day, probably three thousand generations may have intervened, and yet the present living specimen is specifically identical with the delineation of its ancestor. The great comparative anatomist Cuvier examined the mummy of an ibis, from three to four thousand years old, comparing it minutely with a living bird of the present day, and found the two specimens in all respects identically the same.

There is also a bass-relief from the ruins of Babylon, with a dog represented upon it, which is found by naturalists to be identical with a species of the dog existing in Asia at the present day.

Evidence of Fossil Remains

But we have still more conclusive evidence than this derived from ancient monuments of the very great permanence of the characteristics by which different species of plants and animals are distinguished from each other, in the fossil remains which exist in the strata of the earth. By means of these our observations upon the forms of vegetable and animal life which have existed upon our globe may be carried back to an immense antiquity, and extended over so vast a number and variety of species as to furnish us, as it has always been supposed, with all the means of information on this subject that can be desired. It has been thought to be fully proved by these observations that every species which exists upon the earth remains unchanged so long as it exists. When at length its period has expired, it disappears from the field, while new ones are continually arising to take the place of those that are gone. But no one passes, by gradations, into any other; and the lines of distinction by which each is separated from all the rest remain sharp and well-defined from the beginning to the end.