GENERAL KNOWLEDGE NEEDFUL. 345 
only by long-enduring transmission, by inheritance of 
acquired adaptations of the brain, out of originally empiric 
or experiential “knowledge a posteriori” (vol. i. p. 31). 
The objections to the Theory of Descent here discussed 
and refuted are, I believe, the most important which have 
been raised against it; I consider also that I have sufficiently 
proved to the reader their futility. The numerous other 
objections which besides these have been raised against the 
Theory of Development in general, or against its biological 
part, the Theory of Descent in particular, arise either from 
such a degree of ignorance of empirically established facts, 
or from such a want of their right understanding, and from 
such an incapacity to draw the necessary conclusions, that 
it is really not worth the trouble to go further into the 
refutation. There are only some general points in regard 
to which, I should like, in a few words, to draw attention. 
In the first place I must observe, that in order thoroughly 
to understand the doctrine of descent, and to be convinced 
, of its absolute truth, it is indispensable to possess a general 
knowledge of the whole of the domain of biological phe- 
nomena. The theory of descent is a biological theory, and 
hence it may with fairness and justice be demanded that 
those persons who wish to pass a valid judgment upon it 
should possess the requisite degree of biological knowledge. 
Their possessing a special empiric knowledge of this or that 
domain of zoology or botany, is not sufficient; they must 
possess a general insight into the whole series of phenomena, 
at least in the case of one of the three organic kingdoms. 
They ought to know what universal laws result from the 
comparative morphology and physiology of organisms, but 
more especially from comparative anatomy, from the indi- 
