578 
they would probably prevail at the expense of those which 
did not proceed as quickly. If there is no evidence of 
this, there is evidently no variety of structure on which 
Natural Selection can act. 
But it might be said that what is not true in the case of 
fission is true in connection with the phenomenon of con 
jugation. Mr. Spencer argues that,— 
“along with that remai'kable process which, beginning in minute forms 
with what is called conjugation, developed into sexual generation, 
there came into play causes of frequent and marked fortuitous 
variations. The mixtures of constitutional proclivities, made more or 
less unlike by unlikenesses of physical conditions, inevitably led to 
occasional concurrences of forces producing deviations of structure. 
These were, of course, mostly suppressed, but sometimes increased 
by survival of the fittest.”—(p. yj.) 
In reply to this argument, we must ask once more what 
we really mean by “ fortuitous ” variations. All scientific 
people, I suppose, would denounce the idea that these 
variations arise by chance, accepting that word in the 
ordinary unphilosophical sense of the word. If we say 
that these variations arise from causes of which we are 
ignorant, that cannot help any physical or biological 
theory. The scientific man may be compelled to tolerate 
such ignorance as exists for the present, but he denies 
that there is any point beyond which research cannot be 
successful. He believes that there is a physical cause for 
every phenomenon which can be proved to exist. By him 
every problem is regarded as capable of solution, if still 
unsolved. We may apply this principle to two kinds 
of variation : the modifications due to all the conceiv 
able influences which act on organisms, directly or 
indirectly; and the variations which are the inevitable 
result of sexual reproduction, the results of which cannot 
be foreseen by man, but the causes of which would per 
haps be clear if we could see the process which takes