1902] Soiree. 57 



come of causes at present operative, evolution was an unscientific 

 hypothesis rightly rejected by leading comparative anatomists 

 such as Cuvier. Darwin, however, showed (i) that every species 

 tends to multiply at such a rate as would, if unchecked, completely 

 fill the world in a short space of time ; and that so long as the 

 relative numbers of members of the various species inhabiting the 

 globe remained about the same, on an average only two of the 

 young produced by a pair of parents survived ; (2) that no two of 

 any brood or litter were ever exactly the same, and that these 

 individual peculiarities were often inheritable ; (3) that in the 

 struggle for existence which must necessarily ensue between the 

 too numerous progeny of every species some of these slight indi- 

 vidual peculiarities would often determine the survival of their 

 possessors and so be handed on to posterity, and in this way the 

 whole species would slowly change its character. If the species 

 were to spread into two localities where the conditions were dis- 

 similar, different peculiarities would be advantageous in the two 

 cases, and the species would split into two divergent groups or 

 or new species. Three main objections had been made to Dar- 

 win's view (i) that species were separated from one another by 

 a barrier of mutual infertility, whereas the breeds of domestic 

 animals produced by artificial selection were all mutually fertile ; 

 (2) that geological evidence afforded no evidence of gradual 

 transitions such as he postulated, and (3) that if organs were 

 derived originally from small rudiments, such rudiments must have 

 been at first useless, and therefore could not have determined the 

 survival of their possessors. All three difficulties had been 

 completely cleared away by subsequent investigations ; 

 in answer to the first, it had been shown that two extreme 

 varieties of the common European frog refi'sed to breed 

 together though each would breed with intermediate types, 

 so that infertility was of various grades and that no sharp 

 line could be driwn between races and species; with regard 

 to the second difficulty, continued investigation was continually 

 bringing to light series of fossils which exactly agreed with Dar- 

 win's postulates, and lastly, it had been shown that organs were 

 never developed out of useless rudiments but out of simple organs 

 and ultimately out of undifferentiated protopUism in which all the 



