ANTIQUITY OF LIVING SPECIES 191 



artists as they are now, and they do not seem to have 

 undergone any perceptible change since then. Thus a 

 lapse of four or five thousand years has not been 

 accompanied by any recognisable variation in such 

 forms of plant and animal life as can be tendered in 

 evidence. Absence of sensible change in these instances 

 is, of course, no proof that considerable alteration may 

 not have been accomplished in other forms more 

 exposed to vicissitudes of climate and other external 

 influences. But it furnishes at least a presumption 

 in favour of the extremely tardy progress of organic 

 variation. 



If, however, we extend our vision beyond the narrow 

 range of human history, and look at the remains of 

 the plants and animals preserved in those younger for- 

 mations which, though recent when regarded as parts 

 of the whole geological record, must be many thou- 

 sands of years older than the very oldest of human 

 monuments, we encounter the most impressive proofs 

 of the persistence of specific forms. Shells which lived 

 in our seas before the coming of the Ice-Age present 

 the very same peculiarities of form, structure, and 

 ornament which their descendants still possess. The 

 lapse of so enormous an interval of time has not 

 sufficed seriously to modify them. So too with the 

 plants and the higher animals which still survive. 

 Some forms have become extinct, but few or none 

 which remain display any transitional gradations into 

 new species. We must admit that such transitions 

 have occurred, that indeed they have been in progress 

 ever since organised existence began upon our planet, 

 and are doubtless taking place now. But we cannot 



