M Database Inspector (cheetah)
Not logged in. Login


105 rows, page 4 of 27 (4/p)
1 2 3 4 5 6 7 8 9 10 20 27

Export to Excel select * from OriginOfSpecies where subject = '04 - Natural Selection' order by subject, title, ordinal limit 12, 4 (Page 4: Row)
subject
title
ordinal
description
04 - Natural Selection 04-05 - Sexual Selection 20 Amongst birds, the contest is often of a more peaceful character. All those who have attended to the subject, believe that there is the severest rivalry between the males of many species to attract, by singing, the females.

bird
bird


The rock-thrush of Guiana, birds of paradise, and some others, congregate; and successive males display with the most elaborate care, and show off in the best manner, their gorgeous plumage; they likewise perform strange antics before the females, which, standing by as spectators, at last choose the most attractive partner.

Rock Thrush
Rock Thrush

Rock Thrush (female)
Rock Thrush (female)

Bird of Paradise
Bird of Paradise

Bird of Paradise (flower)
Bird of Paradise (flower)


Those who have closely attended to birds in confinement well know that they often take individual preferences and dislikes: thus Sir R. Heron has described how a pied peacock was eminently attractive to all his hen birds.

peacock
peacock


I cannot here enter on the necessary details; but if man can in a short time give beauty and an elegant carriage to his bantams, according to his standard of beauty, I can see no good reason to doubt that female birds, by selecting, during thousands of generations, the most melodious or beautiful males, according to their standard of beauty, might produce a marked effect.

Some well-known laws, with respect to the plumage of male and female birds, in comparison with the plumage of the young, can partly be explained through the action of sexual selection on variations occurring at different ages, and transmitted to the males alone or to both sexes at corresponding ages; but I have not space here to enter on this subject.
04 - Natural Selection 04-05 - Sexual Selection 30 Thus it is, as I believe, that when the males and females of any animal have the same general habits of life, but differ in structure, colour, or ornament, such differences have been mainly caused by sexual selection: that is, by individual males having had, in successive generations, some slight advantage over other males, in their weapons, means of defence, or charms, which they have transmitted to their male offspring alone.

Yet, I would not wish to attribute all sexual differences to this agency: for we see in our domestic animals peculiarities arising and becoming attached to the male sex, which apparently have not been augmented through selection by man.

The tuft of hair on the breast of the wild turkey-cock cannot be of any use, and it is doubtful whether it can be ornamental in the eyes of the female bird; indeed, had the tuft appeared under domestication, it would have been called a monstrosity.

Turkey Cock
Turkey Cock
04 - Natural Selection 04-06 - On the generality of Intercross Between Individuals of the Same Species 10 Illustrations of the Action of Natural Selection:
Full Size
04 - Natural Selection 04-06 - On the generality of Intercross Between Individuals of the Same Species 20 In order to make it clear how, as I believe, natural selection
acts, I must beg permission to give one or two imaginary
illustrations.

Let us take the case of a wolf, which preys on various
animals, securing some by craft, some by strength, and
some by fleetness; and let us suppose that the fleetest prey,
a deer for instance, had from any change in the country
increased in numbers, or that other prey had decreased in
numbers, during that season of the year when the wolf was
hardest pressed for food.

wolf
wolf


Under such circumstances the swiftest and slimmest
wolves would have the best chance of surviving and so
be preserved or selected,- provided always that they
retained strength to master their prey at this or some
other period of the year, when they were compelled to
prey on other animals.

I can see no more reason to doubt that this would be the
result, than that man should be able to improve the fleetness
of his greyhounds by careful and methodical selection, or by
that kind of unconscious selection which follows from each
man trying to keep the best dogs without any thought of
modifying the breed.