130 LAMARCK, HIS LIFE AND WORK 
the first genealogical tree; his phylogeny, in the 
second volume of his Phzlosophie zoologique (p. 463), 
proves that he realized that the forms leading up to 
the existing ones were practically extinct, as we now 
use the word. Lamarck in theory was throughout, 
as Houssay well says, at one with us who are now 
living, but a century behind us in knowledge of the 
facts needed to support his theory. 
In this first published expression of his views on 
paleontology, we find the following truths enumerated 
on which the science is based: (1) The great length of 
geological time ; (2) The continuous existence of ani- 
mal life all through the different geological periods 
without sudden total extinctions and as sudden re- 
creations of new assemblages; (3) The physical envi- 
ronment remaining practically the same throughout in 
general, but with (4) continual gradual but not catas- 
trophic changes in the relative distribution of land 
and sea and other modifications in the physical geog- 
raphy, changes which (5) caused corresponding changes 
in the habitat, and (6) consequently in the habits of 
the living beings; so that there has been all through 
geological history a slow modification of life-forms. 
Thus Lamarck’s idea of creation is evolutzonal rather 
than wnxtformitarian. There was, from his point of 
view, not simply a uniform march along a dead level, 
but a progression, a change from the lower or gener- 
alized to the higher or specialized—an evolution or 
unfolding of organic life. In his effort to disprove 
catastrophism he failed to clearly see that species, as 
we style them, became extinct, though really the 
changes in the species practically amounted to extinc- 
