(Tl 
professor forbes’s views on the life of a species. 
(using the term in the sense of an assemblage of individuals, presenting certain characters in common 
and derived from one original protoplast or stock) passes through a series of phases comparable with 
those which succeed each other in definite order during the life of a single individual—that it has its 
epochs of origin, of maturity, of decline, and of extinction, dependent upon the laws of an inherent 
vitality. This notion has two sources—the one direct, the other indirect. It is not an induction, nor 
pretended to he, hut an hypothesis assumed through apparent analogies. Its first and principal source 
may be discovered in the comparison suggested by certain necessary phases in the duration of a species; 
with others in the life of an individual, such as,—each has its commencement, and each has its cessa¬ 
tion. The second and more indirect source of the notion of the life of a species may be traced in 
apparent analogies half perceived between the centralization of generic groups in time and space, and the 
limited duration of both species and individual. But in this case ideas are compared which are 
altogether and essentially distinct. The nature of this distinction is expressed among the following 
propositions, in which an attempt is made to contrast the respective relations of individual, species, and 
genus to geological time and geographical space. 
A. The individual , whether we restrict the word to the single organism, however produced—or 
extend it to the series of organisms, combined or independent, all being products of a single ovum—has 
but a limited and unique existence in time, which, short as it must be, can be shortened by the influ¬ 
ence of unfavourable circumstances, but which no combination of favouring circumstances can prolong 
beyond the term of life allotted to it according to its kind. 
B. The species —whether we restrict the term to assemblages of individuals resembling each other 
in certain constant characters, or hold in addition, the hypothesis (warranted, as might be shown from 
experience and experiment), that between all the members of such an assemblage, there is the rela¬ 
tionship of family, the relationship of descent, and consequently that they are the descendants of one 
first stock or protoplast (how that protoplast appeared is not part of the question)—is like the in¬ 
dividual insomuch as its relations to time are unique : once destroyed it never re-appears. But (and 
this is the point of view now advocated), unlike the individual, it is continued indefinitely so long as 
conditions favourable to its diffusion and prosperity—that is to say, so long as conditions favourable 
to the production and sustenance of the individual representatives or elements—are continued coinci- 
dently with its existence. 
C. The genus , in whatever degree of extension we use the term, so long as we apply it to an 
assemblage of species intimately related to each other in common and important features of organization, 
appears distinctly to exhibit the phenomenon of centralization in both time and space, though with a 
difference, since it would seem that each genus has a unique centre or area of development in time, 
but in geographical space may present more centres than one. 
1. a:—An individual is a positive reality. 
b:—A species is a relative reality. 
c:—A genus is an abstraction—an idea; but an idea impressed on nature, and not arbitrarily 
dependent on man’s conceptions. 
2. a :—An individual is one. 
/3:—A species consists of many resulting from one. 
7 :—A genus consists of more or fewer of these manies resulting from one, linked together, not 
by a relationship of descent, but by an affinity dependent on a divine idea. 
3. a :—An individual cannot manifest itself in two places at once; it has no extension in space ,• 
its relations are entirely with time ; but the possible duration of its existence is regulated by the law 
of its inherent vitality. 
b :—A species has correspondent and exactly analogous relations with time and space—the duration 
of its existence as well as its geographical extension is entirely regulated by physical conditions. 
c:—A genus has dissimilar, or only partially, comparable relations with time and space, and 
occupies areas in both, having only partial relations to physical conditions. 
