after the age at which its species begins ordinarily to continue its
race; for we cannot suppose offspring to remember anything that
happens to the parent subsequently to the parent's ceasing to
contain the offspring within itself. From the average age,
therefore, of reproduction, offspring should cease to have any
further steady, continuous memory to fall back upon; what memory
there is should be full of faults, and as such unreliable. An
organism ought to develop as long as it is backed by memory--that is
to say, until the average age at which reproduction begins; it
should then continue to go for a time on the impetus already
received, and should eventually decay through failure of any memory
to support it, and tell it what to do. This corresponds absolutely
with what we observe in organisms generally, and explains, on the
one hand, why the age of puberty marks the beginning of completed
development--a riddle hitherto not only unexplained but, so far as I
have seen, unasked; it explains, on the other hand, the phenomena of
old age--hitherto without even attempt at explanation.

Sixthly, those organisms that are the longest in reaching maturity
should on the average be the longest-lived, for they will have
received the most momentous impulse from the weight of memory behind
them. This harmonizes with the latest opinion as to the facts. In
his article of Weismann in the Contemporary Review for May, 1890,
Mr. Romanes writes: "Professor Weismann has shown that there is
throughout the metazoa a general correlation between the natural
lifetime of individuals composing any given species, and the age at
which they reach maturity or first become capable of procreation."
This, I believe, has been the conclusion generally arrived at by
biologists for some years past.

Lateness, then, in the average age of reproduction appears to be the
principle underlying longevity. There does not appear at first
sight to be much connection between such distinct and apparently
disconnected phenomena as 1, the orderly normal progress of
development; 2, atavism and the resumption of feral characteristics;
3, the more ordinary resemblance inter se of nearer relatives; 4,
the benefit of an occasional cross, and the usual sterility of
hybrids; 5, the unconsciousness with which alike bodily development
and ordinary physiological functions proceed, so long as they are
normal; 6, the ordinary non-inheritance, but occasional inheritance
of m