CLASSIFICATION, groups subordinate to groups. Natural system. Rules and
difficulties in classification, explained on the theory of descent with
modification. Classification of varieties. Descent always used in
classification. Analogical or adaptive characters. Affinities, general,
complex and radiating. Extinction separates and defines groups.
MORPHOLOGY, between members of the same class, between parts of the
same individual. EMBRYOLOGY, laws of, explained by variations not
supervening at an early age, and being inherited at a corresponding
age. RUDIMENTARY ORGANS; their origin explained. Summary.
From the first dawn of life, all organic beings are found to resemble
each other in descending degrees, so that they can be classed in groups
under groups. This classification is evidently not arbitrary like the
grouping of the stars in constellations. The existence of groups would
have been of simple signification, if one group had been exclusively
fitted to inhabit the land, and another the water; one to feed on
flesh, another on vegetable matter, and so on; but the case is widely
different in nature; for it is notorious how commonly members of even
the same subgroup have different habits. In our second and fourth
chapters, on Variation and on Natural Selection, I have attempted to
show that it is the widely ranging, the much diffused and common, that
is the dominant species belonging to the larger genera, which vary
most. The varieties, or incipient species, thus produced ultimately
become converted, as I believe, into new and distinct species; and
these, on the principle of inheritance, tend to produce other new and
dominant
species. Consequently the groups which are now large, and which
generally include many dominant species, tend to go on increasing
indefinitely in size. I further attempted to show that from the varying
descendants of each species trying to occupy as many and as different
places as possible in the economy of nature, there is a constant
tendency in their characters to diverge. This conclusion was supported
by looking at the great diversity of the forms of life which, in any
small area, come into the closest competition, and by looking to
certain facts in naturalisation.
I attempted also to show that there is a constant tendency in the forms
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