“3.  The development of these organs is in proportion to their
     employment.

      “4.  New developments are transmitted to offspring.”

He supported especially the last two propositions by a series of examples as to the effects of use and disuse; and the most famous of these, the theory that giraffes had produced their long necks by continually stretching up towards the trees on which they fed, is well known to everyone.  However, the ingenious speculations of Lamarck were unsupported by a sufficient range of actual knowledge of anatomy, and lacked experimental proof.  He entirely failed to convince his contemporaries; and Darwin himself, in a letter to Lyell, declared that he had gained nothing from two readings of Lamarck’s book.  There can be little doubt but that several Continental writers, in particular Haeckel, have exaggerated Lamarck’s services to the development of the idea of evolution.  On the other hand, Lyell, although he strongly opposed the ideas of Lamarck and some curious notions of progressional creation due to the great Agassiz, had prepared the way for Darwin by his advocacy of natural causes and slow changes in opposition to the catastrophic and miraculous views in vogue.  Above all, Herbert Spencer had argued most strenuously in favour of evolution.  Thus, in an important passage quoted by Mr. Clodd from the Leader of March 20, 1852, Spencer had written as follows: 

“Those who cavalierly reject the theory of evolution, as not adequately supported by facts, seem quite to forget that their own theory is not supported by facts at all.  Like the majority of men who are born to a given belief, they demand the most rigorous proof of any adverse belief, but assume that their own needs none.  Here we find, scattered over the globe, vegetable and animal organisms numbering, of the one kind (according to Humboldt) some 320,000 species, and of the other, some 2,000,000 species (see Carpenter); and if to these we add the numbers of animal and vegetable species that have become extinct, we may safely estimate the number of species that have existed, and are existing, on the earth, at no less than ten millions.  Well, which is the most rational theory about these ten millions of species?  Is it most likely that there have been ten millions of special creations; or is it most likely that by continual modifications, due to change of circumstances, ten millions of varieties have been produced, as varieties are being produced still?...  Even could the supporters of the development hypothesis merely shew that the origination of species by the process of modification is conceivable, they would be in a better position than their opponents.  But they can do much more than this.  They can shew that the process of modification has effected, and is effecting, decided changes in all organisms subject to modifying influences....  They can shew that in successive generations these changes