Biology | Page 7

made, have we not a right to believe that we are employing a
useful working hypothesis?
But let us now turn to a second example that will illustrate a class of
phenomena which have thus far almost wholly eluded all attempts to

explain them. The one that I select is at present one of the most
enigmatical cases known, namely, the regeneration of the lens of the
eye in the tadpoles of salamanders. If the lens be removed from the eye
of a young tadpole, the animal proceeds to manufacture a new one to
take its place, and the eye becomes as perfect as before. That such a
process should take place at all is remarkable enough; but from a
technical point of view this is not the extraordinary feature of the case.
What fills the embryologist with astonishment is the fact that the new
lens is not formed in the same way or from the same material as the old
one. In the normal development of the tadpole from the egg, as in all
other vertebrate animals, the lens is formed from the outer skin or
ectoderm of the head. In the replacement of the lens after removal it
arises from the cells of the iris, which form the edge of the optic cup,
and this originates in the embryo not from the outer skin but as an
outgrowth from the brain. As far as we can see, neither the animal itself
nor any of its ancestors can have had experience of such a process.
How, then, can such a power have been acquired, and how does it
inhere in the structure of the organism? If the process of repair be due
to some kind of intelligent action, as some naturalists have supposed,
why should not the higher animals and man possess a similar useful
capacity? To these questions biology can at present give no reply. In
the face of such a case the mechanist must simply confess himself for
the time being brought to a standstill; and there are some able
naturalists who have in recent years argued that by the very nature of
the case such phenomena are incapable of a rational explanation along
the lines of a physico-chemical or mechanistic analysis. These writers
have urged, accordingly, that we must postulate in the living organism
some form of controlling or regulating agency which does not lie in its
physico-chemical configuration and is not a form of physical
energy--something that may be akin to a form of intelligence
(conscious or unconscious), and to which the physical energies are in
some fashion subject. To this supposed factor in the vital processes
have been applied such terms as the "entelechy" (from Aristotle), or the
"psychoid"; and some writers have even employed the word "soul" in
this sense--though this technical and limited use of the word should not
be confounded with the more usual and general one with which we are
familiar. Views of this kind represent a return, in some measure, to

earlier vitalistic conceptions, but differ from the latter in that they are
an outcome of definite and exact experimental work. They are therefore
often spoken of collectively as "neo-vitalism."
It is not my purpose to enter upon a detailed critique of this doctrine.
To me it seems not to be science, but either a kind of metaphysics or an
act of faith. I must own to complete inability to see how our scientific
understanding of the matter is in any way advanced by applying such
names as "entelechy" or "psychoid" to the unknown factors of the vital
activities. They are words that have been written into certain spaces
that are otherwise blank in our record of knowledge, and as far as I can
see no more than this. It is my impression that we shall do better as
investigators of natural phenomena frankly to admit that they stand for
matters that we do not yet understand, and continue our efforts to make
them known. And have we any other way of doing this than by
observation, experiment, comparison and the resolution of more
complex phenomena into simpler components? I say again, with all
possible emphasis, that the mechanistic hypothesis or machine-theory
of living beings is not fully established, that it may not be adequate or
even true; yet I can only believe that until every other possibility has
realty been exhausted scientific biologists should hold fast to the
working program that has created the sciences of biology. The vitalistic
hypothesis may be held, and is held, as a matter of faith; but we cannot
call it science without misuse of the word.
When we turn, finally, to the genetic or historical part of our task, we
find ourselves confronted with precisely the same general problem as in
case of the