THE BEGINNINGS OF THINGS (_continued_)
We have now considered, as far as is compatible with the character of a
work of this kind, the beginning and development of the embryo taken as
a whole, and for the remaining part of our study of this subject we may
devote our attention to the beginnings of some of the more important
organs and functions in the new individual. It will be impossible to
deal in detail with all the important parts which ultimately constitute
the new personality, but a selection may be made which will give some
general idea of how great results spring from very small beginnings.
What will be said here it may be hoped will be just sufficient to
stimulate the interest of those to whom the subject appeals, and who may
then turn their attention to some of the larger works which go into
greater detail in this subject, a list of which will be found in the
bibliography at the end of this volume.
It must be remembered that quite a large number of the characteristics
that we usually associate with a normal human being only come into
existence, or at any rate only become obvious, at some period longer or
shorter after birth. True, these characteristics depend for their
ultimate appearance upon the development of the corresponding structures
and organs in the growing embryo, but in the case of some of these,
those organs are not fully developed in embryonic life, and the
manifestation of the functions associated with them may be delayed
perhaps for years. This is notably the case, for example, with the
reproductive organs which, though developed during the life of the
embryo, remain functionless until the period of adolescence. The
development of the human mind and intellect too, although depending, of
course, upon the embryonic growth of the brain and the nervous system
generally, is a matter of time and the environment subsequent to birth.
It should be realised, however, in this connection, that the mind of the
new individual, and all that is involved in that term, dates back
ultimately, as regards its possibilities, to the moment at which the two
germ-cells from the male and female respectively united in
fertilisation. The adult mind develops from the mind of the infant. The
infant mind appears as the result of the possibilities and the
tendencies which were inherent in the germ-cells from which not merely
the brain but the whole embryo sprang; in other words, all that a single
human mind connotes results from the possibilities in a single cell.
Such a thought is a startling one indeed, and at first sight appears,
perhaps, somewhat incredible. But a moment's careful attention to the
problem will show at once that it is in reality no more wonderful than
the fact that this single cell produces all the millions of other cells
which in due time give rise to the skin, bone, nerve, blood, and so
forth, which make up the entire body of the embryo. The human mind,
therefore--and indeed the human soul, if that term be used in any
intelligible sense--takes its origin in the products of the
multiplications of germ-cells acted upon by their subsequent
surroundings.[1]
[1] The detailed study of this part of the subject is dealt
with in the writer's work, _The Greatest Life_ (Duckworth, London),
to which readers who are interested in this phase of the subject are
referred.
With this passing reference to the fact that some important parts of an
individual only grow to their full manifestations after embryonic life,
we may pass to the consideration of the development of some of the more
interesting parts of the embryo itself.
Amongst the most striking, and certainly the most interesting, of the
various parts of the developing embryo, those which go to form the
special senses are prominent. They are interesting not merely from their
actual mode of growth, but especially also in connection with their
evolutionary history. The study of how they have come into their present
state in the higher animals leads us back to very small
beginnings--indeed, to the time when there was no such thing as special
sense organs for sight, hearing, smell, and so forth, but where the
organism had what may be termed a diffused tactual sense over and
throughout the entire body. In the course of time this diffused general
sense became specialised, no better example of which could be quoted
than that of the sense of sight, which was referred to, as many of our
readers will doubtless remember, in Tyndall's famous Belfast address. He
was referring to Herbert Spencer's theory of the manner in which vision
was evolved. He pointed out that, as above noted, in the lowest
organisms sensation is a general thing diffused throughout the body, a
kind of general tactual sense. As the result of environment, and gradual
adaptation to external influences, certain parts of the general surface
of the organism became more responsive to these external stimuli than
other parts. These areas, being those points at which sensation was most
acutely felt, were nothing more or less than primitive sense organs.
Thus in the progress of evolution the stimulus of the eye gradually
became most pronounced in certain cells which contain pigment, these
cells being more responsive to the light stimulus than the rest of the
body. That was the beginning of an eye; a group of cells more receptive,
more easily influenced by light, than any other cells. In a slightly
higher stage of evolution we find a special overgrowth of the skin which
covers over the area in which these pigmented cells lie, obviously a
protective measure on behalf of the specialised cells referred to. Then,
still later, a lens is added, and the whole organ becomes more and more
adapted to the necessities of the case, until it reaches the
extraordinary perfection that is seen in the eye of such a bird as an
eagle. On the same general principle, the other special senses also took
their origin from this general diffused tactual sense, certain cells
becoming specially adapted for receiving the stimulus of sound, others
for taste, others for smell, and so forth.