that they do exist;
so far, therefore, the hypothesis does not break down.

But in the next place comes a much more difficult inquiry:--Are the
causes indicated competent to give rise to the phenomena of organic
nature? I suspect that this is indubitable to a certain extent. It is
demonstrable, I think, as I have endeavoured to show you, that they
are perfectly competent to give rise to all the phenomena which are
exhibited by RACES in nature. Furthermore, I believe that they are
quite competent to account for all that we may call purely structural
phenomena which are exhibited by SPECIES in nature. On that point also
I have already enlarged somewhat. Again, I think that the causes assumed
are competent to account for most of the physiological characteristics
of species, and I not only think that they are competent to account
for them, but I think that they account for many things which
otherwise remain wholly unaccountable and inexplicable, and I may say
incomprehensible. For a full exposition of the grounds on which this
conviction is based, I must refer you to Mr. Darwin's work; all that I
can do now is to illustrate what I have said by two or three cases taken
almost at random.

I drew your attention, on a previous evening, to the facts which are
embodied in our systems of Classification, which are the results of
the examination and comparison of the different members of the animal
kingdom one with another. I mentioned that the whole of the animal
kingdom is divisible into five sub-kingdoms; that each of these
sub-kingdoms is again divisible into provinces; that each province may
be divided into classes, and the classes into the successively smaller
groups, orders, families, genera, and species.

Now, in each of these groups, the resemblance in structure among the
members of the group is closer in proportion as the group is smaller.
Thus, a man and a worm are members of the animal kingdom in virtue of
certain apparently slight though really fundamental resemblances which
they present. But a man and a fish are members of the same sub-kingdom
'Vertebrata', because they are much more like one another than either of
them is to a worm, or a snail, or any member of the other sub-kingdoms.
For similar reasons men and horses are arranged as members of the
same Class, 'Mammalia'; men and apes as members of the same Order,
'Primates'; and if there were any animals more like men than they
were like any of the apes, and yet