78 



SCIENCE 



[N. S. Vol. XL. Ko. 1020 



It has been the work of Darwin to accu- 

 mulate a large number of facts and argu- 

 ments, borrowed from the most diverse 

 parts of the physical and biological sci- 

 ences, and to combine the main results of 

 the study of nature in general in order to 

 find a conclusive proof of the idea of 

 Lamarck. Common descent is now ac- 

 knowledged as the natural cause of the 

 unity of organization. Successive slow 

 modifications have produced the great 

 diversity of forms and the diverging lines 

 of evolution which have gradually led to 

 the highest degrees of differentiation. 



But his broad views and comprehensive 

 considerations did not suffice to aiford the 

 desired proof. Comparative anatomy and 

 systematical studies, the knowledge of the 

 laws of the geographical distribution of 

 animals and plants and of their gradual 

 development during the geological epochs, 

 could only outline the broad features of the 

 theory. Evidently its basis must be sought 

 in the study of the process by which one 

 species is produced from another. Which 

 is the nature and which are the causes of 

 this process? "Which are the elementary 

 changes which, by numerous repetitions and 

 combinations, have produced the main 

 evolutionary lines of the animal and vege- 

 table kingdom? 



In order to answer these questions, 

 Darwin studied the experience of the 

 breeders. The improvement of domestic 

 animals was well known at his time, the 

 cultivated races of flowers and vegetables, 

 of cereals and sugar-beets clearly and 

 widely surpassed the same species in nature. 



The method of breeders is based on the 

 principles laid down about the middle of the 

 last century (1840) by P. P. A. Leveque de 

 Vilmorin, the father of the celebrated 

 founder of the culture of sugar-beets. He 

 had observed the high degree of variability 

 of cultivated plants and discovered that by 



means of a choice of the best samples and 

 by their isolation highly improved varieties 

 may be produced. His son has applied this 

 principle to the sugar-beets, one of the most 

 variable of all cultivated forms, and suc- 

 ceeded in increasing the amount of sugar 

 from 7 to 14 per cent. This improvement 

 soon became the basis of a large sugar- 

 industry in many countries of Europe. 

 Prom that time isolation and selection have 

 become the watchwords of a big new 

 industry, which soon produced the most un- 

 expected results in almost all parts of agri- 

 cultural practise. 



Darwin transplanted this principle of 

 practise into pure science. He studied the 

 variability of species in the wild condition 

 and found it as widely spread and as rich 

 in its features as in cultivated forms. He 

 saw that very many species are distributed 

 in nature in such a way as to constitute 

 numbers of isolated colonies, sufficiently dis- 

 tant from one another to exclude the pos- 

 sibility of intercrossing. He discovered the 

 great factor which replaces artificial selec- 

 tion in nature and called it by the name 

 of natural selection. It is the unceasing 

 struggle for existence and the victory of 

 the most endowed individuals. In nature, 

 every plant produces more seeds than can 

 develop into new plants, owing to lack of 

 space. Only those which are most fit for 

 the surrounding conditions will survive, 

 whilst the remainder are condemned to dis- 

 appear. In this manner the struggle for 

 life leads to a selection, which will be re- 

 peated in every generation, and a whole 

 colony may gradually change by this means 

 until at the end the characters are suffi- 

 ciently different from the original ones to 

 constitute a new variety or even an ele- 

 mentary species. 



Natural selection in the struggle for life 

 has now become the main principle of 

 organic evolution. Since species obey in 



