45 6 THE HISTORY OF BIOLOGY 



in 1875, ^^^^^ having some years previously lost both his sight and his wife, 

 who had been the mainstay of his life and his work. 



Ly ell's act uali Stic geology 

 Like Hutton, Lyell takes as his starting-point the present form of the earth's 

 surface, studies its changes as the result of various natural influences, and 

 finally draws the conclusion that the same forces have always, and approxi- 

 mately in the same degree as in our own time, been operating on the earth's 

 surface; he who declares otherwise must substantiate his argument with 

 proofs; it is the upholders of the catastrophe theory whose duty it is to 

 prove the correctness of their views, and not vice versa. This conception of 

 the evolution of the earth — it has been named the "actualistic" — forces 

 Lyell to follow it through to its extreme consequences and far beyond what 

 science in modern time is prepared to admit. Thus, in his Principles of Geol- 

 ogy he absolutely denies the possibility of the earth's having originally 

 existed in an incandescent state; he likewise definitely rejects Lamarck's 

 theory that the animal world in earlier ages consisted of entirely different 

 species from those in modern times and declares that mammals and birds 

 have existed from the very earliest times. But apart from these extravagant 

 statements, which as a matter of fact he afterwards partly corrected, his 

 strict adherence to the principle that the phenomena of past ages should 

 be explained from what is known from the phenomena of the present time 

 has formed the basis on which it has been possible to construct a truly 

 scientific geology. The earlier geological theories, both ingenious and fool- 

 ish, had all been mere products of the imagination; Lyell introduced the 

 principle, which must inevitably be adopted by every empirical science, of 

 starting from what is known and has been investigated and thence pro- 

 ceeding gradually towards the more remote and the unknown. If past natu- 

 ral phenomena in general are to be calculated or at least reconstructed with 

 fair probability, it is necessary to start from the present, whose course 

 of events it is possible to survey. This astronony has long done with its 

 calculations of the position and motions of the heavenly bodies in past ages; 

 and modern geology has in certain spheres, as, for instance, in the deter- 

 mination of annual stratifications out of water during preceding periods, 

 reached a degree of accuracy that should not be far inferior to astronomi- 

 cal calculation. And this principle essentially represents Lyell's service to 

 science. 



His criticism of La7narck 

 Moreover, Lyell has made important contributions in his above-mentioned 

 work to problems of the development of life upon the earth. His criticism 

 of Lamarck's theory undeniably touches the latter's weakest spot, when he 

 maintains that Lamarck never even attempted to find out the origin of a 

 single vital organ, but merely occupies himself with modifications in those 



