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Export to Excel select * from OriginOfSpecies where ordinal = '40' order by subject, title, ordinal limit 36, 4 (Page 10: Row)
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13 - Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Or 13-05 - Descent always used in classification 40 Geographical distribution may sometimes be brought usefully into play in classing large and widely-distributed genera, because all the species of the same genus, inhabiting any distinct and isolated region, have in all probability descended from the same parents.

We can understand, on these views, the very important distinction between real affinities and analogical or adaptive resemblances.

Lamarck first called attention to this distinction, and he has been ably followed by Macleay and others.

Jean Baptiste Lamarck
Jean Baptiste Lamarck

William Sharp Macleay
William Sharp Macleay
13 - Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Or 13-08 - Extinction separates and defines groups 40 We shall certainly never succeed in making so perfect a collection: nevertheless, in certain classes, we are tending in this direction; and Milne Edwards has lately insisted, in an able paper, on the high importance of looking to types, whether or not we can separate and define the groups to which such types belong.

Henri Milne Edwards
Henri Milne Edwards


Finally, we have seen that natural selection, which results from the struggle for existence, and which almost inevitably induces extinction and divergence of character in the many descendants from one dominant parent-species, explains that great and universal feature in the affinities of all organic beings, namely, their subordination in group under group.

We use the element of descent in classing the individuals of both sexes and of all ages, although having few characters in common, under one species; we use descent in classing acknowledged varieties, however different they may be from their parent; and I believe this element of descent is the hidden bond of connexion which naturalists have sought under the term of the Natural System.

On this idea of the natural system being, in so far as it has been perfected, genealogical in its arrangement, with the grades of difference between the descendants from a common parent, expressed by the terms genera, families, orders, &c., we can understand the rules which we are compelled to follow in our classification.

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.

We can clearly see how it is that all living and extinct forms can be grouped together in one great system; and how the several members of each class are connected together by the most complex and radiating lines of affinities.

We shall never, probably, disentangle the inextricable web of affinities between the members of any one class; but when we have a distinct object in view, and do not look to some unknown plan of creation, we may hope to make sure but slow progress.
14 - Recapitulation and Conclusion 14-01 - Recapitulation of the difficulties on the theory of Natural Selection 40 Turning to geographical distribution, the difficulties encountered on the theory of descent with modification are grave enough.

All the individuals of the same species, and all the species of the same genus, or even higher group, must have descended from common parents; and therefore, in however distant and isolated parts of the world they are now found, they must in the course of successive generations have passed from some one part to the others.

We are often wholly unable even to conjecture how this could have been effected.

Yet, as we have reason to believe that some species have retained the same specific form for very long periods, enormously long as measured by years, too much stress ought not to be laid on the occasional wide diffusion of the same species; for during very long periods of time there will always be a good chance for wide migration by many means.

A broken or interrupted range may often be accounted for by the extinction of the species in the intermediate regions.

It cannot be denied that we are as yet very ignorant of the full extent of the various climatal and geographical changes which have affected the earth during modern periods; and such changes will obviously have greatly facilitated migration.

As an example, I have attempted to show how potent has been the influence of the Glacial period on the distribution both of the same and of representative species throughout the world.

We are as yet profoundly ignorant of the many occasional means of transport.

With respect to distinct species of the same genus inhabiting very distant and isolated regions, as the process of modification has necessarily been slow, all the means of migration will have been possible during a very long period; and consequently the difficulty of the wide diffusion of species of the same genus is in some degree lessened.
14 - Recapitulation and Conclusion 14-02 - Recapitulation of the general and special circumstances in its favour 40 If then we have under nature variability and a powerful agent always ready to act and select, why should we doubt that variations in any way useful to beings, under their excessively complex relations of life, would be preserved, accumulated, and inherited?

Why, if man can by patience select variations most useful to himself, should nature fail in selecting variations useful, under changing conditions of life, to her living products?

What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature, -- favouring the good and rejecting the bad?

I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life.

The theory of natural selection, even if we looked no further than this, seems to me to be in itself probable.