[FOR THE USE OF MEMBERS. | 
Royal Justitutton of Great Britatir. 
1852. 
WEEKLY EVENING MEETING, 
Friday, May 7. 
W. R. Grove, Esq. M.A. F.R.S. Vice President, in the Chair. 
Proressor Epwarp Forsss, F.R.S. 
On the supposed Analogy between the Life of an Individual and the 
Duration of a Species. 
In Natural History and Geology a clear understanding of the rela- 
tions of Individual, Species, and Genus to Geological Time and 
Geographical Space is of essential importance. Much, however, of 
what is_generally received concerning these relations will scarcely 
bear close investigation. Among questionable, though popular no- 
tions upon this subject the Lecturer would place the belief that the 
term of duration of a species is comparable and of the same kind 
with that of the life of an individual. 
The successive phases in the complete existence of an individual 
are Birth, Youth, Maturity, Decline, and Decay terminating in Death. 
Whether we regard an individual as a single self-existing organism 
however produced, or extend it to the series of organisms, combined 
or independent, all being products of a single ovum, its term of 
duration can be abbreviated but not prolonged indefinitely, nor can 
the several phases of its existence be repeated. Conditions may 
arrest or hasten maturity, or prematurely destroy, but cannot, how- 
ever favourable, reproduce a second maturity after decline has com- 
menced. 
Now, it is believed by many that a species (using the term in the . 
sense of an assemblage of individuals presenting certain constant 
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. 
If this notion be true the theory of Geology will be proportion- 
ately affected; since in this case the duration of species must be 
regarded as only influenced, not determined, by the. physical condi- 
tions among which they are placed ;—and, thus, species should 
characterise epochs or sections of time, independent of all physical 
changes and modifying influences short of those which are absolutely 
No. 13. P 
