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Export to Excel select * from OriginOfSpecies where ordinal = '40' order by subject desc limit 12, 4 (Page 4: Row)
subject Desending Order (top row is last)
title
ordinal
description
06 - Difficutiles in Theory 06-13 - Summary: The Law of Unity of Type and of the Conditions of Existence Embraced by the Theory of Natural Selection 40 Although the belief that an organ so perfect as the eye could have been formed by natural selection, is enough to stagger any one; yet in the case of any organ, if we know of a long series of gradations in complexity, each good for its possessor, then, under changing conditions of life, there is no logical impossibility in the acquirement of any conceivable degree of perfection through natural selection.
eye
eye


In the cases in which we know of no intermediate or transitional states, we should be extremely cautious in concluding that none can have existed, for the metamorphoses of many organs show what wonderful changes in function are at least possible.

For instance, a swimbladder has apparently been converted into an air-breathing lung.
Swim Bladder
Swim Bladder

lungs
lungs


The same organ having performed simultaneously very different functions, and then having been in part or in whole specialised for one function; and two distinct organs having performed at the same time the same function, the one having been perfected whilst aided by the other, must often have largely facilitated transitions.
06 - Difficutiles in Theory 06-12 - Organs not in all Cases Absolutely Perfect 40 With respect to the belief that organic beings have been created beautiful for the delight of man,- a belief which it has been pronounced is subversive of my whole theory,- I may first remark that the sense of beauty obviously depends on the nature of the mind, irrespective of any real quality in the admired object; and that the idea of what is beautiful, is not innate or unalterable.
06 - Difficutiles in Theory 06-11 - Organs of Small Importance 40 In the second place, we may easily err in attributing importance to characters, and in believing that they have been developed through natural selection.

We must by no means overlook the effects of the definite action of changed conditions of life,- of so-called spontaneous variations, which seem to depend in a quite subordinate degree on the nature of the conditions,- of the tendency to reversion to long-lost characters,- of the complex laws of growth, such as of correlation, compensation, of the pressure of one part on another, &c.,- and finally of sexual selection, by which characters of use to one sex are often gained and then transmitted more or less perfectly to the other sex, though of no use to this sex.

But structures thus indirectly gained, although at first of no advantage to a species, may subsequently have been taken advantage of by its modified descendants, under new conditions of life and newly acquired habits.
06 - Difficutiles in Theory 06-08 - Means of Transition 40 According to this view it may be inferred that all vertebrate animals with true lungs are descended by ordinary generation from an ancient and unknown prototype, which was furnished with a floating apparatus or swimbladder.

We can thus, as I infer from Owen's interesting description of these parts, understand the strange fact that every particle of food and drink & which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs, notwithstanding the beautiful contrivance by which the glottis is closed. In the higher Vertebrate the branchiae have wholly disappeared- but in the embryo the slits on the sides of the neck and the loop-like course of the arteries still mark their former position.

But it is conceivable that the now utterly lost branchiae might have been gradually worked in by natural selection for some distinct purpose: for instance, Landois has shown that the wings of insects are developed from the tracheae; it is therefore highly probable that in this great class organs which once served for respiration have been actually converted into organs for flight.
gills
gills

Swim Bladder
Swim Bladder

lungs
lungs

wings
wings