RECAPITULATION 283 



any more than the rock-pigeon is directly intermediate in 

 crop and tail between its descendants, the pouter and 

 fantail pigeons. We should not be able to recognize a 

 species as the parent of another and modified species, if 

 we were to examine the two ever so closely, unless we 

 possessed most of the intermediate links; and owing to 

 the imperfection of the geological record, we have no just 

 right to expect to find so many links. If two or three, 

 or even more linking forms were discovered, they would 

 simply be ranked by many naturalists as so many new 

 species, more especially if found in different geological 

 sub-stages, let their differences be ever so slight. Numer- 

 ous existing doubtful forms could be named which are 

 probably varieties; but who will pretend that in future 

 ages so many fossil links will be discovered that natural- 

 ists will be able to decide whether or not these doubtful 

 forms ought to be called varieties? Only a small portion 

 of the world has been geologically explored. Only 

 organic beings of certain classes can be preserved in 

 a fossil condition, at least in any great number. Many 

 species when once formed never undergo any further 

 change, but become extinct without leaving modified de- 

 scendants; and the periods during which species have 

 undergone modification, though long as measured by 

 years, have probably been short in comparison with the 

 periods during which they retained the same form. It 

 is the dominant and widely ranging species which vary 

 most frequently and vary most, and varieties are often at 

 first local — both causes rendering the discovery of inter- 

 mediate links in any one formation less likely. Local 

 varieties will not spread into other and distant regions 

 until they are considerably modified and improved; and 



