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Intersting
explanation of natural selection -Real Player
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Darwin's Basic Premise
Darwin's On the Origin of Species by Means of Natural
Selection, or the Preservation of Favoured Races in the
Struggle for Life, made several points that had major impact
on nineteenth-century thought:
 1.That
biological types or species do not have a fixed, static
existence but exist in permanent states of change and
flux;
2.that all life, biologically considered, takes the form of
a struggle to exist -- more exactly, to exist and produce
the greatest number of offspring;
3.that
this struggle for existence culls out those organisms less
well adapted to any particular ecology and allows those
better adapted to flourish -- a process called Natural
Selection;
4.that
natural selection, development, and evolution requires
enormously long periods of time, so long, in fact, that the
everyday experience of human beings provides them with no
ability to interpret such histories;
5.that the genetic variations ultimately producing increased
survivability are random and not caused (as religious
thinkers would have it) by God or (as Lammarck would have
it) by the organism's own striving for perfection.
The effect of all these points was to move man away from
the center of creation and imply that God could hardly be
nature's driving force. These are direct quotes from
Darwin's book Origin Of The Species, in which he
outlines his theory.
1.
The struggle for existence: Nothing is easier than to
admit in words the truth of the universal struggle for
life, or more difficult -- at least I have found it so --
than constantly to bear this conclusion in mind. Yet
unless it be thoroughly engrained in the mind I am
convinced that the whole economy of nature, with every
fact on distribution, rarity, abundance, extinction, and
variation, will be dimly seen or quite misunderstood. We
behold the fact of nature bright with gladness, we often
see superabundance of food;we do not see, or we forget,
that the birds which are idly singing round us mostly
live on insects or seeds, and are thus constantly
destroying life. . . . I use the term Struggle for
Existence in a large and metaphorical sense, including
dependence of one being on another, and including (which
is more important) not only the life of the individual,
but success in leaving progeny. . . . As more individuals
are produced than can possibly survive, there must in
every case be a struggle for existence, either one
individual with another of the same species, or with the
individuals of distinct species, or with the physical
conditions of life. It is the doctrine of Malthus applied
with manifold force to the whole animal and vegetable
kingdoms (Chapter 3, "Struggle for Existence").
2.
Darwin's emphasis upon abundance (and his use of
metaphor): In looking at Nature, it is most necessary to
keep the foregoing considerations always in mind -- never
to forget that every single organic being around us may
be said to be striving to the utmost to increase in
numbers; that each lives by a struggle at some period of
its life; that heavy destruction inevitably falls either
on the young or old, during each generation or at
recurrent intervals. Lighten any check, mitigate the
destruction ever so little, and the number of the species
will almost instantaneously increase to any amount. The
face of Nature may be compared to a yielding surface,
with ten thousand sharp wedges packed close together and
driven inwards by incessant blows, sometimes one wedge
being struck, and then another with greater force
(Chapter 3).
3.
(A) Adaptation for survival; (B) Relation in opposition:
The structure of every organic being is related, in the
most essential yet often hidden manner, to that of all
other organic beings, with which it comes into
competition for food or residence, or from which it has
to escape, or on which it preys. This is obvious in the
structure of the teeth and talons of the tiger; and in
that of the legs and claws of the parasite which clings
to the hair on the tiger's body. But in the beautifully
plumed seed of the dandelion, and in the flattened and
fringed legs of the water-beetle, the relation seems at
first confined to the elements of air and water. Yet the
advantage of plumed seeds no doubt stands in the closest
relation to the land being already thickly clothed by
other plants; so that the seeds may be widely distributed
and fall on unoccupied ground. In the water-beetle, the
structure of its legs, so well adapted for diving, allows
it to compete with other aquatic insects, to hunt for its
own prey, and to escape serving as prey to other animals
(Chapter 3).
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