48 'WHAT IS A SPECIES? 1 



by the naturalist of the future. Nearly half a century 

 has passed since those words were written. For more 

 than a generation the central ideas of the Origin have 

 been an essential part of the intellectual equipment, not 

 only of every naturalist, but of every moderately intelligent 

 man. What then is the meaning of the word ' species ' 

 to-day, and how does it differ from that of the years 

 before July i, 1858, when the Darwin- Wallace conception 

 of Natural Selection was first launched upon the world ? 

 The present occasion is specially favourable for this 

 inquiry, because we have just been given two additional 

 volumes of the letters of Charles Darwin. After the 

 three volumes published in 1887, naturalists were cer- 

 tainly unprepared for the welcome revelation of such 

 a mine of wealth. The work is all the more valuable 

 because it contains many letters from Alfred Russel 

 Wallace and Sir Joseph Hooker, thus giving both sides 

 of a part of their correspondence with Darwin. Then in 

 1900 the Life and Letters of Thomas Henry Huxley 

 appeared, so that we are now admitted ' behind the veil ', 

 and can read, as never before, the central thoughts of the 

 great makers of biological history. On the publication of 

 the last-named work, I took occasion to combat the view 

 that the thousand closely-printed pages might have been 

 reduced by omitting and condensing many of the letters. 

 The serious student of those stirring years requires the 

 opportunity of thinking over and comparing all the avail- 

 able thoughts and opinions of the chief actors in the 

 memorable scene ; and the very repetition of certain 

 ideas, which proves their persistence and dominance in 

 the writer's mind, is a matter of deep importance and 

 interest. However it may be to the general reader, the 

 student would deprecate the omission or condensation 

 of any of the writings of Darwin or Huxley. The 

 special interest and value in the letters of these men 

 depend on the fact that their inmost convictions on subjects 

 of the deepest scientific importance are to be read, often 

 in the compass of a brief sentence. There we find, as we 

 cannot find in any other way, the real core of the matter, 

 with all accessory and surrounding considerations stripped 



