220 The Science of Life. 



pleasures and pains, and many of these acquired forms 

 or propensities are transmitted to their posterity." 



Lamarck (1744-1829) worked out with greater care 

 than any of his predecessors a logically consistent 

 theory of evolution. In many ways it closely resembled 

 that of Erasmus Darwin, but there is no evidence that 

 Lamarck was acquainted with his writings. Like 

 Buffon, by whom he was undoubtedly influenced, he 

 passed through a stage of avowed belief in the immuta- 

 bility of species, but, having reached an evolutionary 

 position, he excelled his master in the courage of his 

 convictions and in unwavering consistency. He was 

 one of the first to free himself from the untenable con- 

 ception of a linear genetic series, and to develop that 

 of a branching genealogical tree (1809). In regard to 

 the factors of evolution, he agreed with Buffon and 

 differed from Erasmus Darwin as to the direct influence 

 of the environment upon plants, which he believed to be 

 directly modified by changes of soil, heat, light, &c. ; 

 on the other hand, as regards animals, he differed from 

 Buffon and agreed with Erasmus Darwin as to the 

 indirect action of the environment in evoking changed 

 functional reactions. "Environment", he said, "can 

 effect no direct changes whatever upon the organization 

 of animals. But great changes in environment bring 

 about changes in the habits of animals. Changes in 

 their wants necessarily bring about parallel changes in 

 their habits. If new wants become constant or very 

 lasting they form new habits, the new habits involve 

 the use of new parts, or a different use of old parts, 

 which results finally in the production of new organs 

 and the modification of old ones " (cit. Osborn, 1894, 

 p. 1 68). As is well known, the fundamental postulate 

 of Lamarck's theory was that changes acquired through 

 functional reaction or direct environmental influence (in 

 the case of plants) were transmissible. This he assumed 

 without seeking to prove it, and apparently without 

 thinking that it required proof. 



Lamarck's four laws read as follows : 



I. Life, by its essential activities (propres forces), 

 continually tends to increase the volume of every body 



