160. 103 
850.1 
Il 
Scientific Proofs versus ‘A Priori’ Assumptions 
NTIL the great impetus had been given by Darwin to the 
acceptance of the Doctrine of Evolution, by the publication 
of his “ Origin of Species,” natural science mainly consisted of the 
observation of facts. Thus, old text-books of botany contained the 
names and descriptions of the various organs of plants with little 
or no attempt to deal with their physiological uses, much less with 
their origins. The old idea, that ‘species’ were fixed entities, 
created as we now see them, with all their organs complete, led 
men tacitly to assume that such descriptions were all that was 
necessary. Botany mostly consisted of the accumulation of morpho- 
logical facts to aid the systematist. If any suggestions were pro- 
posed as to the purpose of this or that organ, the use of which was 
not very obvious, ‘ teleological guesses,’ as they might be called, were 
thought to be amply sufficient to account for them. The Bridge- 
water treatises may be taken as the type of that old method of 
interpretation of ‘uses, which was, in fact, simply that of a prior: 
assumptions without any strictly scientific bases to go upon; by 
which I mean neither any accurate observations nor experiments, 
wherewith to verify the supposed uses. 
Like that of teleology, it has now come to be generally recog- 
nised that the inherent fallacy underlying metaphysics is due to the 
want of external observations and experimental proofs; so that no 
worker in natural science can well be a metaphysician at the same 
time, for the methods of proof—if any such term can be applicable 
to metaphysics at all—lie in opposite directions. The scientific 
student should be satisfied only with objective facts; the meta- 
physician is contented with subjective imaginations. 
Darwin published “The Origin of Species” in 1859. This 
work at once broke down the old ideas of the fixity of species, 
as having been created such, and having unalterable forms; but 
the question immediately arose: How are new forms worked out by 
evolution in nature ? 
Darwin and Dr Wallace simultaneously propounded the theory 
of Natural Selection. Though differing in some important points, 
both based their conclusions on the following statements :— 
(1) That more offspring are born than can ever live to maturity 
and so leave fresh offspring. 
(2) That no two individuals of the same kind are ever abso- 
