slightly differing but yet permanently distinct species, nor was any
reason given why such slight yet constant differences should exist at
all.


_Scientific Opinion before Darwin._

In order to show how little effect these writers had upon the public
mind, I will quote a few passages from the writings of Sir Charles
Lyell, as representing the opinions of the most advanced thinkers in the
period immediately preceding that of Darwin's work. When recapitulating
the facts and arguments in favour of the invariability and permanence of
species, he says: "The entire variation from the original type which any
given kind of change can produce may usually be effected in a brief
period of time, after which no further deviation can be obtained by
continuing to alter the circumstances, though ever so gradually,
indefinite divergence either in the way of improvement or deterioration
being prevented, and the least possible excess beyond the defined limits
being fatal to the existence of the individual." In another place he
maintains that "varieties of some species may differ more than other
species do from each other without shaking our confidence in the reality
of species." He further adduces certain facts in geology as being, in
his opinion, "fatal to the theory of progressive development," and he
explains the fact that there are so often distinct species in countries
of similar climate and vegetation by "special creations" in each
country; and these conclusions were arrived at after a careful study of
Lamarck's work, a full abstract of which is given in the earlier
editions of the _Principles of Geology_.[2]

Professor Agassiz, one of the greatest naturalists of the last