Quotes About Variation

Let it also be borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other and to their physical conditions of life; and consequently what infinitely varied diversities of structure might be of use to each being under changing conditions of life.

Sexual selection will also be largely dominated by natural selection tending towards the general welfare of the species.

For forms existing in larger numbers will always have a better chance, within any given period, of presenting further favourable variations for natural selection to seize on, than will the rarer forms which exist in lesser numbers.

It seems pretty clear that organic beings must be exposed during several generations to the new conditions of life to cause any appreciable amount of variation; and that when the organisation has once begun to vary, it generally continues to vary for many generations.

there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be NATURALLY SELECTED.

They also carried on commerce with other nations. All this clearly shows, as Heer has remarked, that they had at this early age progressed considerably in civilisation; and this again implies a long continued previous period of less advanced civilisation, during which the domesticated animals, kept by different tribes in different districts, might have varied and given rise to distinct races.

A grand and almost untrodden field of inquiry will be opened, on the causes and laws of variation, on correlation of growth, on the effects of use and disuse, on the direct actions of external conditions, and so forth.

He who believes that each being has been created as we now see it, must occasionally have felt surprise when he has met with an animal having habits and structure not at all in agreement.

Showing that they descend from common parents, and consequently must be ranked as varieties.

It has already been stated that various parts in the same individual, which are exactly alike during an early embryonic period, become widely different and serve for widely different purposes in the adult state. So again it has been shown that generally the embryos of the most distinct species belonging to the same class are closely similar, but become, when fully developed, widely dissimilar.

El aislamiento también es un elemento importante en la modificación de las especies por medio de la selección natural. En un área limitada o aislada, si no es muy grande, serán generalmente casi uniformes las condiciones orgánicas e inorgánicas de la vida, de modo que la selección natural tenderá a modificar de la misma manera a todos los individuos que varíen en la misma especie.

Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare? Yet these relations are of the highest importance, for they determine the present welfare, and, as I believe, the future success and modification of every inhabitant of this world.

puede llegar a deducir que las especies no han sido creadas independientemente, sino que han descendido como variedades de otras especies.

immutable productions

like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, etc., as the only possible cause of variation. In one very

I have called this principle, by which each slight variation, if useful, is preserved, by the term natural selection, in order to mark its relation to man's power of selection. But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient.

unusual degree. This family became divided eight generations

We shall best understand the probable course of natural selection by taking the case of a country undergoing some slight physical change, for instance, of climate. The proportional numbers of its inhabitants will almost immediately undergo a change, and some species will probably become extinct.

What natural selection cannot do, is to modify the structure of one species, without giving it any advantage, for the good of another species; and though statements to this effect may be found in works of natural history, I cannot find one case which will bear investigation.

las variaciones y diferencias individuales favorables, y la destrucción de aquellas que son nocivas, es lo que hemos llamado selección natural o supervivencia de los más aptos.

But that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species.

Puede decirse metafóricamente que la selección natural está haciendo diariamente, y hasta por horas, en todo el mundo, el escrutinio de las variaciones más pequeñas; desechando las que son malas, conservando y acumulando las que son buenas, trabajando insensible y silenciosamente donde y cuando se presenta una oportunidad, en el mejoramiento de todo ser orgánico en relación con sus condiciones orgánicas e inorgánicas de vida.

The differences of Mr. [Patrick] Matthew's views from mine are not of much importance: he seems to consider that the world was nearly depopulated at successive periods, and then re-stocked;

On peut démontrer ainsi ni la stérilité ni la fécondité ne fournissent aucune distinction certaines entre les espèces et les variétés.