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Autumn 1875

Sterility &c

One great character of a living organism is that it can form, from inorganic material, tissue like itself

This character is Growth or Nutrition or Reproduction

Another character is that they it possess the power of "replying" to changes in their its environment─ The most characteristic important kind of "replying" is the power of changing form shape in answer to certain changes in their environment ─ eg the shrinking of a mass of protoplasm on being touched ─ But a change in the environment not only produces this change of form but it produces its effect on the process of growth, so that the character of every fresh increment to the tissue of an organism will depend on the nature of the environment at the during the period of growth of that increment─

Out of the simple irritability of protoplasm has been built up the nervous system─ & the most highly organised animals have the most highly organised nervous systems.

We see why this is when we consider that individual organism have only will succeeded in developing from a low to high state existing within best way by only by the most delicate adjustment of themselves to external changes ─ & that the nervous system is by a part of the body being specialised to be extremely sensitive of change ─ the body both gains a kind of magnifying glass to inform it of the slightest change in its environment, and leaves the in & has the rest of itself left free to be developed into the other organs necessary to meet such changes

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So far we have only considered the individual ─ now The difference between an indi individual and a group of individuals is just illustrated by the difference between Nutrition (or the increase in size of the indiv), and Reproduction (or the increase in size of the group)─ Thus in low organisms Reproduction is only the splitting off of a bit piece of body new tissue produced by Nutrition─ If an organism always produced by nutritionnew portions of tissue which were identical are with another ─ Then when Nutrition supplemented by fusion gave rise to Reproduction we should have a group of organisms each precisely alike But we have seen that a great character of living individual organisms is the power of varying or replying both by irritability & by differences in the character of their growth ─ to changes in their environment ─ It follows therefore that no two individuals of a group will be absolutely identical─

Let us If we now compare the life of all individual with the life of a species ─ Those individua fact that the most highly organised animals have the most highly developed nervous systems points to the conclusion

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Let us compare the life of the Indiv with that of the group of Individuals

Life being the adaptation of internal change to external change ─ it follows that an animal that adapts itself most delicately to external change is the highest animal─ The nervous system is a part of the body specialised to exaggerate be extremely sensitive to external change ─ it thus it acting like a magnifying glass for the rest of the body & making each part sensible of changes which could not otherwise have affected them ─ And since it is impossible that an animal should be sensitive very delicate in it's the adaptation of itself to external changes, without being easily sensible of such changes in it follows that to be highly organised developed it must have a highly developed nervous system.

On In the same way no species group of individu

The life of a group of individuals considered as a group has nothing to do with separate existence of its group constituents ─ its life consists merely in the reproduction of the group over and over again in successive generations ─ The only activity it possesses is that of Reproduction ─ If we suppose that the circumst environment of a group of individuals ie if ─ a species ─ is slowly varying in a certain direction, then if the act of reproduction

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that the individuals composing such highly organised groups have better then any other animals solved the problem of existence ─ that is they adapt themselves more delicately than any other animals to changes in their environment

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goes on just as if no change had taken place in the environment the in species will be unable to vary and will therefore die ─ but if the reproductive system is sensitive to change, some kind of variations will be produced & the species will continue to exist through in a slightly changed form ─ (*Just as if we have an animal slowly move over hand I over down into an animal, if it possesses sufficient irritability to shrink away at the change if light caused by the shadow of the hand ─ it will escape ─ in a changed form be it observed)

[several words in the margin illegible]

It is therefore evident that sensitiveness to change will be a necessary quality for a highly organised reproductive system─

If we take a wild animal & pro domesticate it the most one important thing we do is thar we protect it from its enemies & from the need to struggle for life ─ And since in a state of nature it depends for victory in the struggle in the fineness of its senses in the when it is freed from the need to struggle it loses the need of fine senses Unless The lop ear of the rabbit is "an outward & visible sign of the inward & spiritual" loses of nervous sensibility

In the same way a species being tamed species being protected Nat Seln has lost the necessity of being having a reproductive system extremely sensitive to change its the and consequently loses that sensibility ─

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Thus the nervous system & the Reproductive systems are two specialisations of properties originally inherent in all parts of the bodies of the lower animals ─

The Nervous system has been developed by the needs of the individual life

The Reproductive system by the needs of the life of the species ─

The nervous system has two main functions the perception of external change and the produ regulation of internal change

The Reproductive System is usually supposed to have but one function the production of a new individual attached that it is produces the regulation of internal change what I mean is imagine that it must possess as well something like the specialised sensibility to external change powered by the nervous system─

[in margin by Darwin:] I think it must have, but incidentally?

If the development of the reproductive system has

There is one more analogy ─ a slight stimulation ie change of a nerve produces increase of its function a [illeg] stimuln prevents it ─ A slight change of circumstances increases function of reproduction a great change prevents it altogether