Artificial selection
In the theory of evolution, artificial selection is the process of intentional or unintentional modification of a species through human actions which encourage the breeding of certain traits over others.Charles Darwin originally coined the term in order to contrast this process from what he called natural selection. He noted that many domesticated animals and plants had special properties that were developed by intentionally encouraging the breeding potential of individuals who both possessed desirable characteristics, and discouraging the breeding of individuals who had less desirable characteristics.
He then postulated that a similar process occurs naturally; individuals in the wild who possess characteristics that enhance their prospects for having offspring would then undergo a similar process of change over time; although in this case "desirable" characteristics would be not those which specifically satisfy human needs, but those which enhance survivability. This natural process forms the basis of the theory of Darwinian evolution.
The most obvious examples of artifical selection can be found in the range of specialised body shapes and even personality types in domesticated dogs. The wide range of sizes and shapes, from dacshund to wolfhound, show the power of artificial selection.
In a more modern sense, human beings are seen as a more integrated part of the whole of our world's ecology, creating a somewhat fuzzier distinction between "natural" and "artificial" selection.
One the one hand, certain characteristics may unintentionally be encouraged while intentionally selecting for a desired result. For example, the domestic chicken has been bred to reach a large size relatively quickly (compared to its feral ancestors). The resulting changes in the chicken's gut have come at the expense of a reduced brain size and relatively smaller leg bones; these latter changes were not intentional artifical selections, but through a parallel process somtimes called "unconcious selection".
On the other hand, human activity in the larger sense creates a new set of unintentional environmental pressures which in turn act in concert with "natural" selection pressures, sometimes in unexpected or ultimately undesirable ways. For example, the general habitat changes caused by the expansion of human communities in North America has tended to select for so-called "weed species" such as the starling and the norwegian rat who thrive in disturbed habitats, while selecting against species such as the spotted owl[?] whose strategies are attuned to a particular stable ecology.
Controversially, examples of artificial selection are sometimes said to be seen in humans themselves, who employ substantial cultural bias in mate selection, most obviously in the preference of human females for socially powerful mates - a factor which isn't directly related to natural ecology or to simple secondary sexual characteristics. Critics of this view point out that selective pressures must be linked to inheritable traits; and that at this point in time, it is unknown which human social traits are inheritable, and which ones are primarily transferred through learning and culture - the so-called "Nature-Nurture" argument.
However, most biologists and evolutionary theorists employ the term artificial selection only to make a distinction between the intentionally human-chosen "artificial" factors and the combination of instinct and ecology that is "natural" without human choice. To describe more deliberate influences on human behavior they may refer to sociobiology, moral selection[?] or ethical selection[?].
External Links
- The Effects of Artifical Selection (http://www.lifesci.utexas.edu/courses/mcmurry/spring98/1/james.html)
Speak the ancient dreams:
You have conquer'd too, one time.
And within your border once
Jew, you had a land one time,
(How it moves the heart!)
Glisten, candles, glisten!
All the grief.html">grief in me,
And the question heard again:
Chanukah Thoughts
Have we been used to weep and sigh,
And seen astonished foemen fly!
We too have rushed into the fray,
And through the spears have fought our way,
And suns arise and set in tears,
Foregone the might of ancient years.
In exile where the wicked reign,
But e'en today each throbbing vein
Have threshed us, yet we have not blenched:
That fire is burning, still unquenched.
Our fall.html">fall is great, our fall is real,
Yet in us lives the old Ideal
Sfere
To laughing with me,--not a word for reply!
And can a Jew laugh when the rule is to cry?
You laughed then, you say? 'tis a sound to affright one!
The laugh of a Jew! It is never a right one,
You deemd that the star of a Jew could be kind?
Jew,--sit down in sackcloth and weep yourself blind!
The garden is green and the woodland rejoices:
But Spring calls not _you_ with her thousand sweet voices!--
In moaning and sighing glides quickly away.
What joy can he find in the splendors of May?
Bewildered and homeless, of whom whoso passes
Say, is it for him to seek flowers and grasses,
On grief and oppression, song.html">song breaks out anew,
And ev'ry note tells me the singer's a Jew.
A skilful musician, and one who is versed
The pitiful song of the Jewish dispersed,
On this, now, alone Jewish fancy is bent.
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