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Natural Selection: the keynote of the Darwinian Theory. The
fittest to survive are not necessarily those which are ideally

most perfect.

Changes in environment. Geological evidence of changes of climate
in England and in Greenland.

Comparison between Natural and Artificial Selection. Natural
Selection acts for the good of the Species. Artificial Selection
is directed solely towards the benefit or the pleasure of Man.

Fossils are the actual remains, as bones, teeth, shells, etc., or the

indications, as, e.g., footprints, of the animals that formerly in-

habited the earth. Amongst them, were our collections com-

plete, would be the entire series of the ancestors of all living

animals. The actual age of Fossils cannot be determined, but

their relative ages are known from the position of the strata in

which they are found.

The Imperfection of the Geological Record. Only certain parts of
certain animals can be preserved as fossils: special conditions
are necessary for their preservation, and for their subsequent
exposure at places accessible to man. It is irrational to expect
fossils to yield continuous series of forms, save under exceptional
circumstances. " A Chapter of Accidents."

The Geological Evidences of Evolution. Life on the earth has been
continuous. Cuvier's Cataclysms have no place in nature. In
passing from the older to the more recent strata, there is a
general advance in organisation, and a gradual approach
towards the existing condition. Fossils are "generalized
forms" rather than directly intermediate links. The geological
history of the Horse, of Birds and Reptiles, and of Paludina.

The Extinction of Species. Persistent types. Comparison of the
Geological Record with the History of Man.

THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

The Problems of Geographical Distribution; and the methods of
attacking them. The clue to the present condition is afforded
by the study of past history.

The Geographical Distribution of Camels, Marsupials, and Tapirs.

THE ARGUMENT FROM EMBRYOLOGY.

Embryology as a clue to Zoological affinities. The development of an
animal often gives us evidence, otherwise unattainable, as to its
relations with other animals or groups of animals. Good illus-
trations of this are afforded by Ascidians, by Barnacles, and by
many groups of Parasitic animals.

The Recapitulation Theory. The doctrine of Evolution tells us that
animals, like men, have pedigrees. The study of Embryology
reveals to us this ancestry, because every animal in its develop-
ment tends to repeat the history of the race.

Illustrations of Recapitulation. The development of Flat fish, Crabs,

Prawns and Barnacles.

Embryology and Paleontology. Examples of Recapitulation as seen
in Fossils. The Shells of Foraminifera and of Mollusca. The
Embryology of Ammonites. The Antlers of Deer.

Rudimentary or Vestigial Organs: structures which are present in a

condition in which they can be of no use to their possessors.

Natural Selection will not account for the formation or

perpetuation of such structures; but the Recapitulation Theory

explains these at once, as organs which were of functional value

to the ancestors of their present possessors, and which appear

in the development of existing forms owing to the tendency to

repeat ancestral characters. Examples of Vestigial Organs:

their Zoological importance.

Causes tending to falsify the Ancestral History as preserved in actual

development.

1. The tendency to condensation of the Ancestral History.

2. The tendency to the omission of Ancestral Stages. The

structure of an egg. Germ yolk and food yolk. The causes
regulating the number and size of the eggs produced by
different animals.

3. The tendency to distortion of Ancestral Stages.

LECTURE V. (Pp. 116-150.)

THE COLOURS OF ANIMALS AND OF PLANTS.

Colour may be non-significant, as in the case of the redness of the
blood of many animals, or the colours of animals living in dark-
ness. More usually, however, colour can be shown to have a
direct relation to the welfare of the individual or species, and to
be attributable to the action of Natural Selection.

Of late years our knowledge on this subject has advanced

greatly, mainly through the observations of Mr. Wallace, sup-

plemented by those of Mr. Bates, Mr. Trimen, Mr. Poulton,

and others.

COLOURS OF ANIMALS.

1. Apatetic Coloration.

Apatetic Coloration serves to hinder recognition: it may be

considered under three heads :-

(a) Protective resemblances : aiding escape from enemies. The

resemblances are usually either to plants, as in the case of the
leaf insects, and stick insects, and of the green coloured cater-
pillars and other frequenters of plants or trees; or else to
inanimate objects, as in the case of the whiteness of the Arctic
Hare, and of other defenceless Arctic animals.

A peculiar and interesting form of protective resemblance is
afforded by the cases of mimicry, in which a defenceless butter-
fly or other animal escapes attack through its superficial
resemblance to a noxious or venomous animal.

(b) Aggressive resemblances are cases in which the object
gained, like that of the wolf in sheep's clothing, is to facilitate
approach to the prey through a superficial resemblance to other

objects. Examples are afforded by the whiteness of the Polar
Bear and other predacious Arctic animals, or the colouring of
the Lion or Tiger.

(c) Alluring resemblances are cases in which the coloration is
such as to cause the animal to resemble a flower or other
attractive object, and so to entice the approach of prey.

Under this head all the cases of Sexual Coloration are

included, in which, as in the Peacock, the bright colouring is
confined to one sex, or is at any rate more marked in it, and is
displayed for the purpose of attracting the opposite sex.

The bright colours of Flowers and of Fruits serve to attract
the insects which fertilise the flowers, and birds and mammals
which secure the dispersal of the seeds.

Cross-Fertilisation. The methods of ensuring cross-fertilisation in

Orchids.

"Natural Selection tends only to make each organic being as per-
fect as, or slightly more perfect than, the other inhabitants of
the same country with which it comes into competition." "It
will not produce absolute perfection."

"Natural Selection cannot possibly produce any modification in a
species exclusively for the good of another species."

Missing Links. Erroneous ideas as to the true nature of " links,"
and as to their supposed absence. "Links" are nearly always
indirect, rarely direct; they may combine the special charac-
ters of both the forms they connect, but more usually have the
characters of neither. The true link between any two forms is
afforded by the common ancestor from whom both alike are
descended. Examples of links of various kinds.

Persistent Types. Many instances are known of genera of animals

which have persisted, without appreciable modifications in

structure, for enormously long periods, and in some cases from

Silurian times to the present day. The occurrence of such

persistent types is in no way opposed to the Theory of Natural

Selection

Degeneration or Retrograde Development. An animal may be less
highly organised when adult than it is in its earlier stages of
existence. During development, organs such as eyes, legs, etc.,
that are present in the young animals may disappear or become
vestigial. This again is not opposed to the theory of Natural
Selection. Natural Selection tends to preserve those forms
which are best adapted to their environment, and not necessarily
those which are ideally most perfect. Examples of degeneration
of individual organs, and of entire animals.

Difficulty as to the persistence of lowly organised animals alongside the

higher forms.

Alleged uselessness of small variations. The whole theory and practice

of breeding domestic animals depend on selecting the right

animals by scrupulous attention to minute differences. The

objection that the right variation may not be present is met by

the fact that variation affects all organs and occurs in all

directions.

Difficulty as to the earliest commencement of organs. Natural Selection

can only act on an organ after it has already attained sufficient

size to be of practical importance and utility. The Theory of

Change of Function: an organ may lose its original purpose and

yet persist because it is of use for some other purpose: one of

these purposes may predominate at one time, another at

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