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Updated: May 6, 2025
We see why certain characters are far more serviceable than others for classification; why adaptive characters, though of paramount importance to the beings, are of hardly any importance in classification; why characters derived from rudimentary parts, though of no service to the beings, are often of high classificatory value; and why embryological characters are often the most valuable of all.
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.
He is relatively unsheltered from any forces that make for adaptive change, as contrasted with the case of his betters; and however sluggish and reluctant may be his response to such discipline as makes for a displacement of outworn preconceptions, yet it is always out of the mass of this common humanity that those movements of disaffection and protest arise, which lead, on occasion, to any material realignment of the institutional fabric or to any substantial shift in the line of policy to be pursued under the guidance of their betters.
In the evolution, then, of modern locomotives, differences have come about, even though the common ancestor is one single type; and these differences have an adaptive value to certain specific conditions. A second illustration will be useful.
The adaptive relation is not the only common characteristic of these somatic sexual characters. Another most important fact is not only that they are fully developed in one sex, absent or rudimentary in the other, but that their development is connected with the functional maturity and activity of the gonads.
We can understand why we value certain resemblances far more than others; why we are permitted to use rudimentary and useless organs, or others of trifling physiological importance; why, in comparing one group with a distinct group, we summarily reject analogical or adaptive characters, and yet use these same characters within the limits of the same group.
Nothing shows the distinction better than convergent adaptation. Owls resemble birds of prey in bill and claw and mode of life, yet they are related to insect-eating swifts and goat-suckers and not to eagles and hawks. Swifts and swallows are similar in adaptive characters, but not in those which show relationship.
It would be straining the natural possibilities of any bitch to expect her to bring up eighteen puppies healthily. Half that number would tax her natural resources to the extreme. But Nature is extraordinarily adaptive in tempering the wind to the shorn lamb, and a dam who gives birth to a numerous litter ought not to have her family unduly reduced.
He thus explained adaptation to new conditions and divergence of several species from a common ancestor. Characters which were not obviously adaptive were explained either by correlation or by the supposition that they had a utility of which we were ignorant. Darwin also admitted the direct action of conditions as a subordinate factor.
With every exercise of these powers the organ and its corresponding function became better developed. Every gain either in function or in organ was transmitted to those of the next generation, who were thus enabled to start where their parents left off. The general environment constantly gave the stimuli that led to the adaptive changes.
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