42 
IOWA ACADEMY OF SCIENCE Voi.. XXVII, 1920 
In its philosophical aspects the species question is of interest; 
but from that point of view there is no pressing need of solution. 
As a scientific problem, however, it affects our daily work, and 
may become a barrier to progress. 
Much has been said of the ideality versus the reality of the 
species concept. While the conception of a species may be purely 
a matter of the mind ; and while there may still exist the debatable 
question as to whether the group or the individual is the real 
unit in nature ; yet the fact remains that in practice we must have 
a unit. 
When we endeavor to trace the historical development of any 
general idea in science it is customary to look as far back, at 
least, as Aristotle for a starting point. But in this case we do not 
find that Aristotle possessed any clear and defined notion of what 
we now call species. He recognized, and had names for, the 
different kinds of animals and plants, of course; but these dif- 
ferentiations were probably not based upon any generalized 
notions. 
The first definition of species is usually attributed to John Ray, 
the Englishman, who lived in the seventeenth century. The dom- 
inant principle in Ray’s conception was community of descent. 
As interpreted by Hertwig, Ray’s ’definition of species was as 
follows: “For plants there is no other more certain character- 
istic for determining species than their origin from the seeds of 
specifically or individually like parents ; that is to say, generalized 
for all organisms, to one and the same species belong individuals 
which spring from similar ancestors.” 
The next important contribution to the subject was made by 
Linnaeus, who said : “There are as many different species as 
there were different forms created in the beginning by the Infinite 
Being.” (“Species tot sunt diversas formas ab initio creavit 
infinitum ens.”) The problem in Linnaeus’s time was to establish 
the reality of species and their immutability, rather than to ex- 
amine critically the criteria by which they might be recognized. 
Buffon’s definition was: “A constant succession of individuals 
similar to and capable of reproducing each other.” DeCandolle 
defined a species as “an assemblage of ah those individuals which 
resemble each other more than they do others, and which are 
able to reproduce their like, in such a manner that they may be 
supposed by analogy to have descended from a single being or a 
single pair.” 
