shown very low in
the scale, to offspring and apparently to comrades, ought to have come
in more prominently in your table than appears to be the case. Secondly,
if you give any instance of the appreciation of different stimulants by
plants, there is a much better case than that given by you--namely,
that of the glands of Drosera, which can be touched roughly two or three
times and do not transmit any effect, but do so if pressed by a weight
of 1/78000 grain ("Insectivorous Plants" 263). On the other hand, the
filament of Dionoea may be quietly loaded with a much greater weight,
while a touch by a hair causes the lobes to close instantly. This has
always seemed to me a marvellous fact. Thirdly, I have been accustomed
to look at the coming in of the sense of pleasure and pain as one of the
most important steps in the development of mind, and I should think it
ought to be prominent in your table. The sort of progress which I have
imagined is that a stimulus produced some effect at the point affected,
and that the effect radiated at first in all directions, and then that
certain definite advantageous lines of transmission were acquired,
inducing definite reaction in certain lines. Such transmission
afterwards became associated in some unknown way with pleasure or pain.
These sensations led at first to all sorts of violent action, such as
the wriggling of a worm, which was of some use. All the organs of sense
would be at the same time excited. Afterwards definite lines of action
would be found to be the most useful, and so would be practised. But it
is of no use my giving you my crude notions.

LETTER 421. TO S. TOLVER PRESTON. Down, May 22nd, 1880.

(421/1. Mr. Preston wrote (May 20th, 1880) to the effect that
"self-interest as a motive for conduct is a thing to be commended--and
it certainly [is] I think...the only conceivable rational motive of
conduct: and always is the tacitly recognised motive in all rational
actions." Mr. Preston does not, of course, commend selfishness, which is
not true self-interest.

There seem to be two ways of looking at the case given by Darwin. The
man who knows that he is risking his life,--realising that the personal
satisfaction that may follow is not worth the risk--is surely admirable
from the strength of character that leads him to follow the social
instinct against his purely personal inclination. But the man who
blindly obeys the social instinct is a more useful member of a socia