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06 - Difficutiles in Theory 06-12 - Organs not in all Cases Absolutely Perfect 90 How the sense of beauty in its simplest form- that is, the reception of a peculiar kind of pleasure from certain colours, forms, and sounds- was first developed in the mind of man and of the lower animals, is a very obscure subject.

The same sort of difficulty is presented, if we enquire how it is that certain flavours and odours give pleasure, and others displeasure.

Habit in all these cases appears to have come to a certain extent into play; but there must be some fundamental cause in the constitution of the nervous system in each species.
06 - Difficutiles in Theory 06-12 - Organs not in all Cases Absolutely Perfect 100 Natural selection cannot possibly produce any modification in a species exclusively for the good of another species; though throughout nature one species incessantly takes advantage of, and profits by, the structures of others.

But natural selection can and does often produce structures for the direct injury of other animals, as we see in the fang of the adder, and in the ovipositor of the ichneumon, by which its eggs are deposited in the living bodies of other insects.
adder
adder

ichneumon
ichneumon


If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection.

Although many statements may be found in works on natural history to this effect, I cannot find even one which seems to me of any weight.

It is admitted that the rattlesnake has a poison-fang for its own defence, and for the destruction of its prey; but some authors suppose that at the same time it is furnished with a rattle for its own injury, namely, to warn its prey.
rattlesnake
rattlesnake


I would almost as soon believe that the cat curls the end of its tail when preparing to spring, in order to warn the doomed mouse.
cat
cat

mouse
mouse
06 - Difficutiles in Theory 06-12 - Organs not in all Cases Absolutely Perfect 110 It is a much more probable view that the rattlesnake uses its rattle, the cobra expands its frill, and the puff-adder swells whilst hissing so loudly and harshly, in order to alarm the many birds and beasts which are known to attack even the most venomous species.

rattlesnake
rattlesnake

adder
adder


Snakes act on the same principle which makes the hen ruffle her feathers and expand her wings when a dog approaches her chickens; but I have not space here to enlarge on the many ways by which animals endeavour to frighten away their enemies.
chicken
chicken

dog
dog


Natural selection will never produce in a being any structure more injurious than beneficial to that being, for natural selection acts solely by and for the good of each.

No organ will be formed, as Paley has remarked, for the purpose of causing pain or for doing an injury to its possessor.

If a fair balance be struck between the good and evil caused by each part, each will be found on the whole advantageous.

After the lapse of time, under changing conditions of life, if any part comes to be injurious, it will be modified; or if it be not so, the being Will become extinct as myriads have become extinct.
06 - Difficutiles in Theory 06-12 - Organs not in all Cases Absolutely Perfect 120 Natural selection tends only to make each organic being as perfect as, or slightly more perfect than, the other inhabitants of the same country with which it comes into competition.

And we see that this is the standard of perfection attained under nature.

The endemic productions of New Zealand, for instance, are perfect one compared with another; but they are now rapidly yielding before the advancing legions of plants and animals introduced from Europe.
New Zealand
New Zealand

Europe
Europe


Natural selection will not produce absolute perfection, nor do we always meet, as far as we can judge, with this high standard under nature.

The correction for the aberration of light is said by Muller not to be perfect even in that most perfect organ, the human eye.
eye
eye


Helmholtz, whose judgment no one will dispute, after describing in the strongest terms the wonderful powers of the human eye, adds these remarkable words: "That which we have discovered in the way of inexactness and imperfection in the optical machine and in the image on the retina, is as nothing in comparison with the incongruities which we have just come across in the domain of the sensations.

One might say that nature has taken delight in accumulating contradictions in order to remove all foundation from the theory of a pre-existing harmony between the external and internal worlds."

If our reason leads us to admire with enthusiasm a multitude of inimitable contrivances in nature, this same reason tells us, though we may easily err on both sides, that some other contrivances are less perfect.

Can we consider the sting of the bee as perfect, which, when used against many kinds of enemies, cannot be withdrawn, owing to the backward serratures, and thus inevitably causes the death of the insect by tearing out its viscera?
bee
bee