External and Internal Factors in- Evolution 301 



that of Lamarck. The central idea of Geoffroy's view was 

 that species of animals and plants undergo change as the 

 environment changes ; and it is important to note, in passing, 

 that he did not suppose that these changes were always for 

 the benefit of the individual, i.e. they were not always adap- 

 tive. If they were not, the forms became extinct. So long 

 as the conditions remain constant, the species remains con- 

 stant ; and he found an answer in this to Cuvier's argument, 

 in respect to the similarity between the animals living at 

 present in Egypt and those discovered embalmed along with 

 mummies at least two thousand years old. Geoffroy Saint- 

 Hilaire said, that since the climatic conditions of Egypt 

 had remained exactly the same during all these years, the 

 animals of Egypt would also have remained unchanged. 



Geoffroy's views were largely influenced by his studies in 

 systematic zoology and by his conception of a unity of plan 

 running through the entire animal kingdom. His study of 

 embryology and paleontology had led him to believe that 

 present forms have descended from other organisms living in 

 the past, and in this connection his discovery of teeth in the 

 jaws of the embryo of the baleen whale and also his dis- 

 covery of the embryonic dental ridges in the upper and in 

 the lower jaws of birds, were used with effect in supporting 

 the theory of change or evolution. Lastly, his remarkable 

 work in the study of abnormal forms prepared the way for 

 his conception of sudden and great changes, which he be- 

 lieved organisms capable of undergoing. He went so far in 

 fact, in one instance, as to suppose that it was not impossible 

 that a bird might have issued fully equipped from the egg of 

 a crocodile. Such an extreme statement, which seems to us 

 nowadays only laughable, need not prejudice us against the 

 more moderate parts of his speculation. 



His study of the fossil gavials found near Caen led him 

 to believe that they are quite distinct from living crocodiles. 

 He asked whether these old forms may not represent a link 



