4 INTRODUCTION. 



should be very badly received now-a-days if we were to recon- 

 sider the question upon a burning soil. It has not been so, how- 

 ever. Most Monogenists* have, up to the present time, done the 

 universal wrong of invoking, in proof of their ideas, an autho- 

 rity which it is not allowable to discuss. Science is neither a 

 special attribute of privileged castes, nor given to certain 

 times in preference to others ; it has never been obliged to 

 wait for a revelation; it is universal, and all men, endowed 

 with the same faculties, have always been able, in all countries 

 and at all times, to carry it as far, when they have had the 

 same means and the same occasions of observation ; it is thus 

 that psychology, based upon simple reflection, has not farther 

 progressed in our days than at Athens or at Alexandria ; from 

 Plato to Descartes there is only the distance between one 

 system and the other. 



" Historians of that which is," has said the illustrious chief 

 of the philosophical school of France, Etienne Geoffroy Saint- 

 Hilaire, " we cannot fail, except when we cease to relate the 

 truth." t Now, truth in science cannot be governed except by 

 two means, reasoning after the manner of mathematics, and 

 observation, of which experiment is but a variety. Every idea 

 d priori, every hypothesis is only good if we accept it with a 

 strong determination of abandoning it if the facts are no longer 

 explicable by its means. Without this, its influence is dis- 



* "All monogenists," we said in the first edition of this book. M. de 

 Quatrefages has exclaimed loudly against these words (Unite de I'Espece Hu- 

 maine, 1861, p. 299), and in the same passage has shown himself an open 

 enemy to all mingling of religion in the domain of science. We are too 

 glad of this declaration not to recall it in this place. We should be sorry not 

 to be able always to agree in these pages with the masters of science, with 

 those, indeed, who have been our own. We have been led to touch on 

 several questions already treated of by them, by following another path, 

 by looking at facts from another point of view ; therefore, there are some 

 differences of opinion. Our excuse lies in the universal right of free inquiry ; 

 for the rest, we shall always name the persons with whom we think we do 

 not agree. " Not to do so," as Bayle said, " is in some measure an excess 

 of ceremony prejudicial to the liberty which we ought to enjoy in the re- 

 public of letters; it is to introduce therein works of supererogation. It 

 should be always allowable to name those whom we disprove ; this is sufficient 

 to prevent a bitter, injurious, or dishonest spirit." Dictionnaire Philoso- 

 phique, art. Pereira, note D. 



t E. Geoffroy Saint-Hilaire has not, however, been able to free himself 

 completely from the unhappy influences which we endeavour to oppose. See 

 Comptes rendus de V Academic des Sciences, vol. iv, p. 78. 



