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|OriginOfSpecies - 475 Rows|
|02 - Variations Under Nature||02-03 - Doubtful Species||60||
When a young naturalist commences the study of a group of organisms quite unknown to him, he is at first much perplexed in determining what differences to consider as specific, and what as varietal; for he knows nothing of the amount and kind of variation to which the group is subject; and this shows, at least, how very generally there is some variation.
But if he confine his attention to one class within one country, he will soon make up his mind how to rank most of the doubtful forms.
His general tendency will be to make many species, for he will become impressed, just like the pigeon or poultry fancier before alluded to, with the amount of difference in the forms which he is continually studying; and he has little general knowledge of analogical variation in other groups and in other countries, by which to correct his first impressions.
As he extends the range of his observations, he will meet with more cases of difficulty; for he will encounter a greater number of closely-allied forms.
But if his observations be widely extended, he will in the end generally be able to make up his own mind: but he will succeed in this at the expense of admitting much variation,- and the truth of this admission will often be disputed by other naturalists.
When he comes to study allied forms brought from countries not now continuous, in which case he cannot hope to find intermediate links, he will be compelled to trust almost entirely to analogy, and his difficulties will rise to a climax.
|02 - Variations Under Nature||02-03 - Doubtful Species||70||
Certainly no clear line of demarcation has as yet been drawn between species and sub-species- that is, the forms which in the opinion of some naturalists come very near to, but do not quite arrive at, the rank of species: or, again, between sub-species and well-marked varieties, or between lesser varieties and individual differences. These differences blend into each other by an insensible series; and a series
impresses the mind with the idea of an actual passage.
|02 - Variations Under Nature||02-03 - Doubtful Species||80||
Hence I look at individual differences, though of small interest to the systematist, as of the highest importance for us, as being the first steps towards such slight varieties as are barely thought worth recording in works on natural history.
And I look at varieties which are in any degree more distinct and permanent, as steps towards more strongly-marked and permanent varieties; and at the latter, as leading to sub-species, and then to species.
The passage from one stage of difference to another may, in many cases, be the simple result of the nature of the organism and of the different physical conditions to which it has long been exposed; but with respect to the more important and adaptive characters, the passage from one stage of difference to another may be safely attributed to the cumulative action of natural selection, hereafter to be explained, and to the effects of the increased use or disuse of parts.
A well-marked variety may therefore be called an incipient species; but whether this belief is justifiable must be judged by the weight of the various facts and considerations to be given throughout this work.
|02 - Variations Under Nature||02-01 - Variability||10||
BEFORE applying the principles arrived at in the last chapter to organic beings in a state of nature, we must briefly discuss whether these latter are subject to any variation.
To treat this subject properly, a long catalogue of dry facts ought to be given; but these shall reserve for a future work.
Nor shall I here discuss the various definitions which have been given of the term species.
No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.
Generally the term includes the unknown element of a distant act of creation. The term "variety" is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved.
We have also what are called monstrosities; but they graduate into varieties.
By a monstrosity I presume is meant some considerable deviation of structure, generally injurious, or not useful to the species.
Some authors use the term "variation" in a technical sense, as implying a modification directly due to the physical conditions of life; and "variations" in this sense are supposed not to be inherited; but who can say that the dwarfed condition of shells in the brackish waters of the Baltic, or dwarfed plants on Alpine summits, or the thicker fur of an animal from far northwards, would not in some cases be inherited for at least a few generations?
And in this case I presume that the form would be called a variety.