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Updated: May 10, 2025
So, again, there are cases known of animals which have been thought by naturalists to be undoubted species, which have yielded perfectly fertile hybrids; while there are other species which present what everybody believes to be varieties* which are more or less infertile with one another.
They are alive with men, at least as compared with the solitude which our Scottish Highlands present. I had brought thither my notions of a valley taken from the narrow winding and infertile straths of Scotland, capable of feeding only a few scores of inhabitants. Here I found that a valley might be a country, and contain almost a nation in its bosom.
He liked rivulets better than rivers. He could not bear the sight of the sea; its infertile bosom and blind restless tumblings filled him with melancholy. The ruins of a park affected him more than the ruins of castles. It is true that no plain, however beautiful, ever seemed so in his eyes; he required torrents, rocks, dark forests, mountains, and precipices.
It was formerly supposed that when a union proved infertile, it was the wife who was at fault.
In city life their thrift, industry, and enterprise, unsurpassed in the United Kingdom, have built up a world-wide commerce. In rural life they have drawn the largest yield from relatively infertile soil. Such, in brief, is the achievement of Ulster Protestantism in the realm of industry. It is a story of which, when a united Ireland becomes more than a dream, all Irishmen will be proud.
On the other hand, not only is it not proved that all species give rise to hybrids infertile inter se, but there is much reason to believe that, in crossing, species exhibit every gradation from perfect sterility to perfect fertility. Such are the most essential characteristics of species.
But between species, in many cases, you cannot succeed in obtaining even the first cross: at any rate it is quite certain that the hybrids are often absolutely infertile one with another. Here is a feature, then, great or small as it may be, which distinguishes natural species of animals.
So that with dimorphic species two unions, which may be called legitimate, are fully fertile; and two, which may be called illegitimate, are more or less infertile. With trimorphic species six unions are legitimate, or fully fertile, and twelve are illegitimate, or more or less infertile.
A queer piece of advice, intelligible only if the land was infested with malaria. Many of their luxurious habits assume another import, on this hypothesis. Like the inhabitants of the malarious Etruscan region, they were adepts at draining, and their river is described, in one of the minor works attributed to Galen, as "rendering men infertile" a characteristic result of malaria.
"As we see it now, the main cause of infertile soils or the deterioration of soils is the improper sanitary conditions originally present in the soil or arising from our injudicious culture and rotation of crops. It is, of course, exceedingly difficult to work out the principles which govern the proper rotation for any particular soil."
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