HUXLEY OX MAX’S PLACE IX XATTJRE. 
383 
u greater structural barrier from the brutes than they are from one 
c< another—then it seems to follow that if any physical process of 
“ connection can be discovered by which the genera and families of 
“ ordinary animals have been produced, that process of connection is 
“ amply sufficient to account for the origin of Man. In other words, 
“ if it could be shown that the Marmosets, for example, have arisen 
Si by gradual modification of the ordinary I J lcityrliini or that both 
“ Marmosets and Flatyrhini , are modified ramifications of a primitive 
“ stock—then there would be no external ground for doubting that 
“ man might have originated, in the one case, by the gradual modi- 
“ fication of a manlike ape—or in the other case as a ramification of 
“ the same primitive stock as these apes.” 
At the present moment Prof. Huxley is of opinion that there is 
“ only one such physical process of connection with any evidence in 
“ its favour,” namely, that suggested by Mr. Darwin. Prof. Huxley 
is also of opinion that Mr. Darwin has satisfactorily proved first, that 
what is termed “ Selection or Selective modification ” “ must occur 
“ and does occur in natureand secondly , that “ such selection is com- 
“ petent to produce forms as distinct structurally as some genera 
“ are.” But in addition to their structural differences, species of 
animals and plants exhibit also 'physiological characters, and the 
question is, is Mr. Darwin’s hypothesis consonant with the observed 
physical divergences of species ? 
As regards one important physiological character it seems that this 
is not the case. “ So long as all the animals and plants certainly pro- 
“ duced by selective breeding from a common stock are fertile inter se, 
“ we have a fact that the Darwinian hypothesis will not explain. Por 
“ what are known as distinct species structurally are for the most 
“ part either altogether incompetent to breed with one another, or 
“ if they breed, their progeny is not fertile inter se.” Prof. Huxley 
therefore adopts Mr. Darwin’s hypothesis, “ subject to the production 
“ of proof that physiological species may be produced by selective 
“ breeding: just as a physical philosopher may accept the un- 
“ dulatory theory of light subject to the proof of the existence of 
“ hypothetical ether; or as the chemist adopts the atomic theory, 
“ subject to the proof of the existence of atoms ; and for exactly the 
“ same reasons, namely, that it has an immense primd facie proba- 
“ bility; that it is the only means at present within reach of 
“ reducing the chaos of observed facts to order; and lastly, that it 
“ is the most powerful instrument of investigation which has been 
“ presented to naturalists since the invention of the natural system 
“ of classification and the commencement of the systematic study of 
u embryology.” 
“ But, even leaving Mr. Darwin’s views aside,” continues Prof. 
Huxley, “the whole analogy of natural operations furnishes so 
“ complete and crushing an argument against the intervention of any 
“ but what are termed secondary causes in the production of all the 
“ phenomena of the universe ; that in view of the intimate relations 
