ON THE GENETIC VIEW OF NATURE. 



365 



the mechanical and eosmical importance was clearly fore- 

 seen by Lord Kelvin in 1852, but which is hardly 

 assimilated yet by scientific, much less by popular, 

 thought. 



The two doctrines of the conservation of matter and 

 of energy would lead to the idea that nature is a kind 

 of perpetuum mobile, nothing in the way of matter or 

 energy being lost ; and that such a reversal of her pro- 

 cesses is possible as we are accustomed to deal with in 

 purely mechanical contrivances. But a closer examina- 

 tion of the processes of nature, as distinguished from 

 those of artificial machines, revealed the fact that, 



speaks of " periods of mutation " 

 i.e., of rapid change of species, of 

 which he gives various instances. 

 He concludes that " as many steps 

 as the organisation has taken since 

 the beginning, so many periods of 

 'mutation' must have existed." 

 He considers the vital processes to 

 be built up out of "units." "Of 

 such units there are probably in 

 the higher plants several thousands, 

 and their ancestors must have run 

 through as many periods of muta- 

 tation." He concludes with the 

 following words : " Although such 

 calculations are naturally exposed 

 to much criticism, they neverthe- 

 less lead on very different roads to 

 identical results. Lord Kelvin, 

 who a few years ago collected and 

 examined critically the various data 

 .referring to. this subject, arrives at 

 the conclusion that provisionally, 

 and with all reservations, the dura- 

 tion of life on the earth can be 

 placed at 24 millions of years. We 

 accordingly take this figure for our 

 biochronic equation. And as we 

 can with great probability estimate 

 the number of elementary pro- 

 perties in one of the higher plants 



at some thousands, it follows that 

 the interval of time between two 

 periods of mutation must have 

 lasted several thousands of years." 

 (See de Vries's Address to the Ger- 

 man Assoc. of Science at Hamburg 

 in 1891, ' Verhandelungen,' &c., p. 

 202, &c. ; also Lord Kelvin (Phil. 

 Mag. (5.) 47, p. 66). Mr Wallace 

 has, from an entirely different point 

 of view, been led to the conclusion 

 that " certain definite portions of 

 man's intellectual and moral nature 

 could not have been developed by 

 variation and natural selection alone, 

 and that, therefore, some other in- 

 fluence, law, or agency is required 

 to account for them." This would 

 account for an apparent, though 

 perhaps not an actual, break in the 

 continuity of all natural processes, 

 which, in the dictum natura non 

 facit saltum, has received a very 

 general expression and acceptance. 

 This dictum supported by the 

 authority of Leibniz is, however, 

 by some modern thinkers de- 

 nounced as a scholastic and anti- 

 quated aphorism. (See Yves 

 Delage, 'L t Here"dite',' &c., p. 266.) 



