M Database Inspector (cheetah)
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|OriginOfSpecies - 475 Rows|
|14 - Recapitulation and Conclusion||14-06 - Concluding remarks||20||
As all the living forms of life are the lineal descendants of those which lived long before the Silurian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world.
Hence we may look with some confidence to a secure future of equally inappreciable length.
And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us.
These laws, taken in the largest sense, being Growth with Reproduction; inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms.
Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows.
There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
|01 - Variations Under Domestication||01-04 - Inheritance||20||
Any variation which is not inherited is unimportant for us.
But the number and diversity of inheritable deviations of structure, both those of slight and those of considerable physiological importance, are endless. Dr. Prosper Lucas's treatise, in two large volumes, is the fullest and the best on this subject.
No breeder doubts how strong is the tendency to inheritance; that like produces like is his fundamental belief: doubts have been thrown on this principle only by theoretical writers.
When any deviation of structure often appears, and we see it in the father and child, we cannot tell whether it may not be due to the same cause having acted on both; but when amongst individuals, apparently exposed to the same conditions, any very rare deviation, due to some extraordinary combination of circumstances, appears in the parent- say, once amongst several million individuals- and it reappears in the child, the mere doctrine of chances almost compels us to attribute its reappearance to inheritance.
Every one must have heard of cases of albinism, prickly skin, hairy bodies, &c., appearing in several members of the same family.
If strange and rare deviations of structure are really inherited, less strange and commoner deviations may be freely admitted to be inheritable.
Perhaps the correct way of viewing the whole subject would be, to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly?
|13 - Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Or||13-03 - Rules and difficulties in classification, explained on the theory of descent with modification||40||
Any one of these characters singly is frequently of more than generic importance, though here even when all taken together they appear insufficient to separate Cnestis from Connarus.' To give an example amongst insects, in one great division of the Hymenoptera, the antennae, as Westwood has remarked, are most constant in structure; in another division they differ much, and the differences are of quite subordinate value in classification; yet no one probably will say that the antennae in these two divisions of the same order are of unequal physiological importance.
Any number of instances could be given of the varying importance for classification of the same important organ within the same group of beings.
Again, no one will say that rudimentary or atrophied organs are of high physiological or vital importance; yet, undoubtedly, organs in this condition are often of high value in classification.
No one will dispute that the rudimentary teeth in the upper jaws of young ruminants, and certain rudimentary bones of the leg, are highly serviceable in exhibiting the close affinity between Ruminants and Pachyderms.
Robert Brown has strongly insisted on the fact that the rudimentary florets are of the highest importance in the classification of the Grasses.
|02 - Variations Under Nature||02-06 - Many of the Species included within the Larger Genera resemble Varieties in being very closely, but unequally, related to each other, and in having restricted ranges||20||
And what are varieties but groups of forms, unequally related to each other, and clustered round certain forms- that is, round their parent-species. Undoubtedly there is one most important point of difference between varieties and species; namely, that the amount of difference between varieties, when compared with each other or with their parent-species, is much less than that between the species of the same genus.
But when we come to discuss the principle, as I call it, of Divergence of Character, we shall see how this may be explained, and how the lesser differences between varieties tend to increase into the greater differences between species.
There is one other point which is worth notice.
Varieties generally have much restricted ranges: this statement is indeed scarcely more than a truism, for, if a variety were found to have a wider range than that of its supposed parent-species, their denominations would be reversed.
But there is reason to believe that the species which are very closely allied to other species, and in so far resemble varieties, often have much restricted ranges.
For instance, Mr. H. C. Watson has marked for me in the well-sifted London Catalogue of Plants (4th edition) 63 plants which are therein ranked as species, but which he considers as so closely allied to other species as to be of doubtful value: these 63 reputed species range on an average over 6.9 of the provinces into which Mr. Watson has divided Great Britain. Now, in this same Catalogue, 53 acknowledged varieties are recorded, and these range over 7.7 provinces; whereas, the species to which these varieties belong range over 14.3 provinces.
So that the acknowledged varieties have nearly the same
restricted average range, as have the closely allied forms, marked for me by Mr. Watson as doubtful species, but which are almost universally ranked by British botanists as good and true species.