2014年 09月 09日
wiki見てたら"ダーウィンは、『種の起源』の中で、evolution ではなく、Descent with modification という単語を使っている。これは Evolution という語が進歩や前進を意味しており、ダーウィンは進化にそのような意味を込めていなかったからである。" とあったので The Origin of Species を眺めてみた。
The Origin of Species
"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."
一方、変化を伴う由来（Descent with modification）の方はそこら中にでてきた。
In 1846 the veteran geologist N. J. d'Omalius d'Halloy published in an excellent though short paper ("Bulletins de l'Acad. Roy Bruxelles,' tom. xiii. p. 581) his opinion that it is more probable that new species have been produced by descent with modification than that they have been separately created: the author first promulgated this opinion in 1831.
May not those naturalists who, knowing far less of the laws of inheritance than does the breeder, and knowing no more than he does of the intermediate links in the long lines of descent, yet admit that many of our domestic races have descended from the same parents may they not learn a lesson of caution, when they deride the idea of species in a state of nature being lineal descendants of other species?
The term 'variety' is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved.
There is no exception to the rule that every organic being naturally increases at so high a rate, that if not destroyed, the earth would soon be covered by the progeny of a single pair. Even slow-breeding man has doubled in twenty-five years, and at this rate, in a few thousand years, there would literally not be standing room for his progeny. Linnaeus has calculated that if an annual plant produced only two seeds and there is no plant so unproductive as this and their seedlings next year produced two, and so on, then in twenty years there would be a million plants. The elephant is reckoned to be the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase: it will be under the mark to assume that it breeds when thirty years old, and goes on breeding till ninety years old, bringing forth three pairs of young in this interval; if this be so, at the end of the fifth century there would be alive fifteen million elephants, descended from the first pair.
So it is when we travel northward, but in a somewhat lesser degree, for the number of species of all kinds, and therefore of competitors, decreases northwards; hence in going northward, or in ascending a mountain, we far oftener meet with stunted forms, due to the directly injurious action of climate, than we do in proceeding southwards or in descending a mountain. When we reach the Arctic regions, or snow-capped summits, or absolute deserts, the struggle for life is almost exclusively with the elements.
"descendants" "descends" 等54カ所
Natural Selection * its power compared with man's selection * its power on characters of trifling importance * its power at all ages and on both sexes * Sexual Selection * On the generality of intercrosses between individuals of the same species * Circumstances favourable and unfavourable to Natural Selection, namely, intercrossing, isolation, number of individuals * Slow action * Extinction caused by Natural Selection * Divergence of Character, related to the diversity of inhabitants of any small area, and to naturalisation * Action of Natural Selection, through Divergence of Character and Extinction, on the descendants from a common parent * Explains the Grouping of all organic beings
Difficulties on the theory of descent with modification * Transitions * Absence or rarity of transitional varieties * Transitions in habits of life * Diversified habits in the same species * Species with habits widely different from those of their allies * Organs of extreme perfection * Means of transition * Cases of difficulty * Natura non facit saltum * Organs of small importance * Organs not in all cases absolutely perfect * The law of Unity of Type and of the Conditions of Existence embraced by the theory of Natural Selection
No complex instinct can possibly be produced through natural selection, except by the slow and gradual accumulation of numerous, slight, yet profitable, variations. Hence, as in the case of corporeal structures, we ought to find in nature, not the actual transitional gradations by which each complex instinct has been acquired for these could be found only in the lineal ancestors of each species but we ought to find in the collateral lines of descent some evidence of such gradations; or we ought at least to be able to show that gradations of some kind are possible; and this we certainly can do.
For no amount of exercise, or habit, or volition, in the utterly sterile members of a community could possibly have affected the structure or instincts of the fertile members, which alone leave descendants. I am surprised that no one has advanced this demonstrative case of neuter insects, against the well-known doctrine of Lamarck.
He who can read Sir Charles Lyell's grand work on the Principles of Geology, which the future historian will recognise as having produced a revolution in natural science, yet does not admit how incomprehensibly vast have been the past periods of time, may at once close this volume.
From these and similar considerations, but chiefly from our ignorance of the geology of other countries beyond the confines of Europe and the United States; and from the revolution in our palaeontological ideas on many points, which the discoveries of even the last dozen years have effected, it seems to me to be about as rash in us to dogmatize on the succession of organic beings throughout the world, as it would be for a naturalist to land for five minutes on some one barren point in Australia, and then to discuss the number and range of its productions.
Several facts in distribution, such as the great difference in the marine faunas on the opposite sides of almost every continent, the close relation of the tertiary inhabitants of several lands and even seas to their present inhabitants, a certain degree of relation (as we shall hereafter see) between the distribution of mammals and the depth of the sea, these and other such facts seem to me opposed to the admission of such prodigious geographical revolutions within the recent period, as are necessitated in the view advanced by Forbes and admitted by his many followers.
Would it be thought sufficient to say that because planets revolve in elliptic courses round the sun, satellites follow the same course round the planets, for the sake of symmetry, and to complete the scheme of nature? An eminent physiologist accounts for the presence of rudimentary organs, by supposing that they serve to excrete matter in excess, or injurious to the system; but can we suppose that the minute papilla, which often represents the pistil in male flowers, and which is formed merely of cellular tissue, can thus act?
When the views entertained in this volume on the origin of species, or when analogous views are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history.
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.