" {39}

Those who accept evolution insist on unbroken physical continuity between
the earliest known life and ourselves, so that we both are and are not
personally identical with the unicellular organism from which we have
descended in the course of many millions of years, exactly in the same
way as an octogenarian both is and is not personally identical with the
microscopic impregnate ovum from which he grew up. Everything both is
and is not. There is no such thing as strict identity between any two
things in any two consecutive seconds. In strictness they are identical
and yet not identical, so that in strictness they violate a fundamental
rule of strictness--namely, that a thing shall never be itself and not
itself at one and the same time; we must choose between logic and dealing
in a practical spirit with time and space; it is not surprising,
therefore, that logic, in spite of the show of respect outwardly paid to
her, is told to stand aside when people come to practice. In practice
identity is generally held to exist where continuity is only broken
slowly and piecemeal, nevertheless, that occasional periods of even rapid
change are not held to bar identity, appears from the fact that no one
denies this to hold between the microscopically small impregnate ovum and
the born child that springs from it, nor yet, therefore, between the
impregnate ovum and the octogenarian into which the child grows; for both
ovum and octogenarian are held personally identical with the newborn
baby, and things that are identical with the same are identical with one
another.

The first, then, and most important element of heredity is that there
should be unbroken continuity, and hence sameness of personality, between
parents and offspring, in neither more nor less than the same sense as
that in which any other two personalities are said to be the same. The
repetition, therefore, of its developmental stages by any offspring must
be regarded as something which the embryo repeating them has already done
once, in the person of one or other parent; and if once, then, as many
times as there have been generations between any given embryo now
repeating it, and the point in life from which we started--say, for
example, the amoeba. In the case of asexually and sexually produced
organisms alike, the offspring must be held to continue the personality
of the parent or parents, and hence on the occasion of every fresh
development, to be repeati