I. Haeckel and His Opponents

It is just this purposeful arrangement which has given rise to the supposition that organic forms cannot be explained in the same way as the facts of inorganic Nature. Kant observes in his Critique of Judgment: “The analogy of the forms, in so far as they seem to be produced in accordance with a common basic plan, despite all differences, strengthens the presumption of a real relationship between them in their generation from a common mother through an approach, step by step, of one animal species to another. ... Here, therefore, it is open to the archaeologist of Nature to cause to arise that great family of creatures (for one would be forced to conceive them thus if the thoroughgoing connected relationship spoken of is to hold good) from the traces left over of her older revolutions, according to all their known and supposed mechanisms. But he must equally for that purpose ascribe to this common mother an organisation purposely fitted to all these creatures, for otherwise the purposive form of the products of the plant and animal kingdoms is unthinkable as to its possibility.”