=== Passages from Origin species ===
This fundamental subject of natural selection will be treated at some
length in the fourth chapter; and we shall then see how natural
almost inevitably causes much extinction of the less improved forms of
life, and leads to what I have called divergence of character.
When, by renewed elevation, the islands were reconverted
into a continental area, there will again have been very severe
competition; the most favoured or improved varieties will have been
to spread; there will have been much extinction of the less improved
and the relative proportional numbers of the various inhabitants of
reunited continent will again have been changed; and again there will
been a fair field for natural selection to improve still further the
inhabitants, and thus to produce new species.
The modified offspring from the later and more highly improved
branches in the lines of descent, will, it is probable, often take the
place of, and so destroy, the earlier and less improved branches:
represented in the diagram by some of the lower branches not reaching
the upper horizontal lines.
Within the same large group, the
later and more highly perfected sub-groups, from branching out and
on many new places in the polity of nature, will constantly tend to
supplant and destroy the earlier and less improved sub-groups. Small
broken groups and sub-groups will finally disappear. Looking to the
future, we can predict that the groups of organic beings which are now
large and triumphant, and which are least broken up, that is, which
yet suffered least extinction, will, for a long period, continue to
as has just been remarked, leads to divergence of character and to
extinction of the less improved and intermediate forms of life. On
principles, the nature of the affinities, and the generally well
distinctions between the innumerable organic beings in each class
throughout the world, may be explained.
=== What does natural selection act solely only on ? ===
As natural selection acts solely by the preservation of profitable
modifications, each new form will tend in a fully-stocked country to
the place of, and finally to exterminate, its own less improved parent-
and other less-favoured forms with which it comes into competition.
extinction and natural selection go hand in hand. Hence, if we look
each species as descended from some unknown form, both the parent and
the transitional varieties will generally have been exterminated by
very process of the formation and perfection of the new form.
=== What can natural selection not do ? ===
To sum up, I believe that species come to be tolerably well-defined
objects, and do not at any one period present an inextricable chaos of
varying and intermediate links: first, because new varieties are very
slowly formed, for variation is a slow process, and natural selection
do nothing until favourable individual differences or variations
until a place in the natural polity of the country can be better
some modification of some one or more of its inhabitants.
=== Improved supplants the less improved ===
It is the same with our domestic productions: when a new and slightly
improved variety has been raised, it at first supplants the less
varieties in the same neighbourhood; when much improved it is
far and near, like our short-horn cattle, and takes the place of other
breeds in other countries. Thus the appearance of new forms and the
disappearance of old forms, both those naturally and artificially
are bound together. In flourishing groups, the number of new specific
forms which have been produced within a given time has at some periods
probably been greater than the number of the old specific forms which
been exterminated; but we know that species have not gone on
increasing, at least during the later geological epochs, so that,
to later times, we may believe that the production of new forms has
the extinction of about the same number of old forms.
NS preserves the most divergent =
As each species tends by its geometrical rate of reproduction to
inordinately in number; and as the modified descendants of each
will be enabled to increase by as much as they become more diversified
habits and structure, so as to be able to seize on many and widely
different places in the economy of nature, there will be a constant
tendency in natural selection to preserve the most divergent offspring
any one species.
=== follows not logically from above ===
Hence during a long-continued course of modification, the
slight differences characteristic of varieties of the same species,
be augmented into the greater differences characteristic of the
the same genus. New and improved varieties will inevitably supplant
exterminate the older, less improved and intermediate varieties; and
species are rendered to a large extent defined and distinct objects.
=== Organs specialized ===
Recent forms are generally looked upon as being, on the whole, higher
in the scale of
organisation than ancient forms; and they must be higher, in so far as
later and more improved forms have conquered the older and less
forms in the struggle for life; they have also generally had their
more specialised for different functions.
=== Extinction of less improved forms ===
These laws, taken in the largest sense,
being Growth with reproduction; Inheritance which is almost implied by
reproduction; Variability from the indirect and direct action of the
conditions of life, and from use and disuse; a Ratio of Increase so
to lead to a Struggle for Life, and as a consequence to Natural
entailing Divergence of Character and the Extinction of less improved
forms. Thus, from the war of nature, from famine and death, the most
exalted object which we are capable of conceiving, namely, the
of the higher animals, directly follows. There is grandeur in this
life, with its several powers, having been originally breathed by the
Creator into a few forms or into one; and that, whilst this planet has
circling on according to the fixed law of gravity, from so simple a
beginning endless forms most beautiful and most wonderful have been,
are being evolved.
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