596 THE POPULAR SCIENCE MONTHLY. 



This question, as being one that strikes the imagination, naturally arose 

 even before science possessed the means of settling it, and preceded, 

 in the historical order, that thorough study of individuals on whfch its 

 solution really depends. When men of science had begun to study 

 living things with other purposes than simply that of deriving from 

 them knowledge that would be available for the medical art, and had 

 gained sufficient information for inductive generalizations, they no 

 longer contented themselves with theories of the origin of groups, but 

 sought to reduce to general principles the structure of living bodies 

 a thing which previously had been considered only from the topo- 

 graphical point of view, and with reference to what was called the use 

 of the parts ; and on these general principles they sought to rest a 

 scientific theory of the origin of natural grouj^s. 



A man of keen and powerful intellect, who, had he but lived in our 

 time, would have attained the summit of fame, with marvelous acu- 

 men anticipated a doctrine which is steadily tending to become a re- 

 ceived scientific theory, viz., that the changes which have occurred in 

 Nature are the efiects of constant natural laws. Ajjplying this idea 

 to the natural groups of the animal kingdom, he rejected the hypothe- 

 sis which ascribed to geological catastrophes the destruction of entire 

 fauniB, and the preparation of the earth's surface for a fresh special 

 creation. The transformation of lower organisms into higher he re- 

 ferred to the action of modifications which, though in themselves in- 

 considerable, became important from repetition and long accumulation, 

 under the influence of forces whose powers he exaggerated. Species 

 and varieties he regarded as artificial groups. According to him the 

 very simplest organisms are derived, by way of spontaneous genera- 

 tion, from naturally-produced plastic substances ; then they mutually 

 diverged by imperceptible difierences, so as to constitute a linear series, 

 which, but for the gaps caused here and there by lost species, would 

 present to us the aspect of a continuous system. Under favoring cir- 

 cumstances the organs of an animal are modified ; a change in the 

 circumstances causes changes in the structure of the individuals be- 

 longing to a species, and is the starting-point for the formation of a 

 new species. Crossing, by producing hybrids, still further multiplies 

 the number of species. And species appear to be fixed, simply because 

 the circumstances appear to be similarly fixed during the brief period 

 embraced in our observations. Transformation is the rule, and in the 

 regular course which it runs we can discover no indications of plan or 

 purpose. 



The ideas of Lamarck, being but ill supported by positive j^roofs, 

 were looked on as mere speculations, plausible but doubtful, or even 

 as dreams, unworthy of science ; his generalizations were discredited, 

 and even now, when they reappear, backed by a powerful array of 

 facts, but few ever think of giving due honor to their author. 



The attempts made at the same period to form generalizations 



