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Export to Excel select * from OriginOfSpecies where ordinal = '10' order by subject limit 56, 4 (Page 15: Row)
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05 - Laws of Variation 05-06 - False Correlation 10 We may often falsely attribute to correlated variation structures which are common to whole groups of species, and which in truth are simply due to inheritance; for an ancient progenitor may have acquired through natural selection some one modification in structure, and, after thousands of generations, some other and independent modification; and these two modifications, having been transmitted to a whole group of descendants with diverse habits, would naturally be thought to be in some necessary manner correlated.
05 - Laws of Variation 05-12 - Reversion to Long Lost Characters 10 No doubt it is a very surprising fact that characters should reappear after having been lost for many, probably for hundreds of generations.

But when a breed has been crossed only once by some other breed, the offspring occasionally show for many generations a tendency to revert in character to the foreign breed- some say, for a dozen or even a score of generations.

After twelve generations, the proportion of blood, to use a common expression, from one ancestor, is only 1 in 2048;
and yet, as we see, it is generally believed that a tendency to reversion is retained by this remnant of foreign blood.

In a breed which has not been crossed, but in which both parents have lost some character which their progenitor possessed, the tendency, whether strong or weak, to reproduce the lost character might, as was formerly remarked, for all that we can see to the contrary, be transmitted for almost any number of generations.

When a character which has been lost in a breed, reappears after a great number of generations, the most probable hypothesis is, not that one individual suddenly takes after an ancestor removed by some hundred generations, but that in each successive generation the character in question has been lying latent, and at last, under unknown favourable conditions, is developed.

With the barb-pigeon, for instance, which very rarely produces a blue bird, it is probable that there is a latent tendency in each generation to produce blue plumage.

Barb Pigeon
Barb Pigeon


The abstract improbability of such a tendency being transmitted through a vast number of generations, is not greater than that of quite useless or rudimentary organs being similarly transmitted. A mere tendency to produce a rudiment is indeed sometimes thus inherited.
05 - Laws of Variation 05-13 - Summary 10 Our ignorance of the laws of variation is profound.

Not in one case out of a hundred can we pretend to assign any reason why this or that part has varied.

But whenever we have the means of instituting a comparison, the same laws appear to have acted in producing the lesser differences between varieties of the same species, and the greater differences between species of the same genus.

Changed conditions generally induce mere fluctuating variability, but sometimes they cause direct and definite effects; and these may become strongly marked in the course of time, though we have not sufficient evidence on this head.

Habit in producing constitutional peculiarities and use in strengthening and disuse in weakening and diminishing organs, appear in many cases to have been potent in their effects.

Homologous parts tend to vary in the same manner, and homologous parts tend to cohere.

Modifications in hard parts and in external parts sometimes affect softer and internal parts.

When one part is largely developed, perhaps it tends to draw nourishment from the adjoining parts; and every part of the structure which can be saved without detriment will be saved.

Changes of structure at an early age may affect parts subsequently developed; and many cases of correlated variation, the nature of which we are unable to understand, undoubtedly occur.

Multiple parts are variable in number and in structure, perhaps arising from such parts not having been closely specialised for any particular function, so that their modifications have not been closely cheeked by natural selection.

It follows probably from this same cause, that organic beings low in the scale are more variable than those standing higher in the scale, and which have their whole organisation more specialised.

Rudimentary organs, from being useless, are not regulated by natural selection, and hence are variable.

Specific characters- that is, the characters which have, come to differ since the several species of the same genus branched off from a common parent- are more variable than generic characters, or those which have long been inherited, and have not differed from this same period.
06 - Difficutiles in Theory 06-11 - Organs of Small Importance 10 As natural selection acts by life and death,- by the survival of the fittest, and by the destruction of the less well-fitted individuals,- I have sometimes felt great difficulty in understanding the origin or formation of parts of little importance; almost as great, though of a very different kind, as in the case of the most perfect and complex organs.