ORIGIN OF MAN. 43
the query whether a blood affinity may not exist between the lowest race and some type of being a little too low to be called human.
The different races of men bear zoologically such characteristics as would be employed to distinguish different species amongst the lower animals. I have heard the elder Agassiz declare that they differ as much as the different families of monkeys. Family distinctions are more profound than specific distinctions. If the various races of men are descended from a common stock, have we not as good grounds for assuming that the domestic dog, the prairiedog, the wolf, the fox and the jackal are also descended from one stock? If parity of reasoning' demands an affirmative response to this question, then the barriers are all down to admission of the derivative origin of organic forms in general. Now, while not affirming a parity of reasoning, it seems appropriate ting state the grounds of derivative doctrine, preparatory
out a disparity of an important kind. The general doctrine of the material continuity of organic forms seems to me to rest on the following classes of evidence:
I. Analogical evidence. Evolution is a law of thought, and hence a law of activity regulated by thought. An idea or concept is first grasped in its general character, then developed in detail. This is the method of the evolution of a sermon or a book. The longer thought dwells on the concept, the more there is evolved from it, under its general and subordinate divisions. This, however, is rather psychological than analogical evidence. But appropriate proof under this head is at hand. The method in the cosmos is a material continuity. Our earth has been what Jupiter is, and has been annulated like Saturn. It has been a sun, self-luminous; it is destined to become, as the moon, a fossil world. So our sun and all suns are in the midst of a progress of an identical kind. So the features of the earth's surface have
become what they are through a continuous series of transitions from older to newer states—from less specialized to more specialized conditions. Again the succession of forms presented by a developing embryo is effected through a material continuity.
The embryo retains its identity in passing through phases as diverse as a tadpole and an elephant—as diverse as a cell and a man.