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{{rewrite|Its role in [[Evolution]] is expressed vaguely. How does natural selection "help" bring a new species into existence? Merely by weeding out the "mistakes"?}}

{{rewrite|Its role in [[Evolution]] is expressed vaguely. How does natural selection "help" bring a new species into existence? Merely by weeding out the "mistakes"?}}

The fundamental statement of '''natural selection''' is that heritable traits which are beneficial will become more numerous in successive generations, while heritable traits which are harmful will become more scarce.  This principle is general, and applies to any system of individuals which reproduce; it is most commonly applied to systems of living organisms.   

The fundamental statement of '''natural selection''' is that heritable traits which are beneficial will become more numerous in successive generations, while heritable traits which are harmful will become more scarce.  This principle is general, and applies to any system of individuals which reproduce; it is most commonly applied to systems of living organisms.   

==General Requirements==

==General Requirements==

== Variation and Randomness ==

== Variation and Randomness ==

Natural selection becomes interesting when there is the possibility of random variation in the duplication of individuals--in other words, when an individual is copied, the copy may be slightly different from the original.  It is important to note that, as stated above, the ''mechanism'' for this variation is not explained or even taken into account by natural selection.  All that matters is that there is ''some'' process that produces variation.  Some of the new, slightly different copies of an individual will be evaluated differently from the original, scoring either higher or lower depending on what changed.  If this process is iterated many times, individuals which score well on the evaluations will become more and more numerous, and the highest score of an individual will tend to rise.  It has been suggested<ref>[Richard Dawkins, ''Climbing Mount Improbable'']</ref> that this process can lead to the appearance of design, as the individuals that are present after many iterations of this process will usually score very well on the evaluation (since those that do not score well are eliminated).

Natural selection becomes interesting when there is the possibility of random variation in the duplication of individuals--in other words, when an individual is copied, the copy may be slightly different from the original.  It is important to note that, as stated above, the ''mechanism'' for this variation is not explained or even taken into account by natural selection.  All that matters is that there is ''some'' process that produces variation.  In this case, some of the offspring of an individual will be better (where "better" is defined as "more likely to successfully reproduce"--one can think of it as scoring higher on an evaluation) and some will be worse.  The higher-scoring offspring will soon come to dominate the population, and over successive generations the average score will also rise.

 

 

Natural selection is a principle that was proposed by [[Charles Darwin]] and Alfred Russel Wallace, who noted that organisms which were better adapted to their environment tended to survive longer and reproduce more than less well-adapted organisms.  Together with [[mutation]] (an altogether distinct phenomenon that should not be confused with natural selection), natural selection forms the basis of evolutionary theory.  As stated above, in any system where selection combines with random variation, successive generations will become better adapted to reproduce.  [[Evolution]] is the theory that this combination of genetic variation (which may be either mutation of the parent or, in most cases, sexual reproduction) and natural selection leads to [[speciation]].

== An Example ==

== An Example ==

An engineer starts with 10,000 different sets of plans for a hydroelectric dam.  His dam must complete two basic tasks: it must hold back a lake with minimal flooding of the surrounding area, and it must maximize power generation.  The intrinsic worth of a dam is determined by how well it completes these tasks; a dam which produces 100 kW of electricity while only raising water levels 2 feet is superior to one which produces 10 kW of electricity while raising water levels 5 feet.  In our simplified example, let us assume that the design of a dam is based on just a few numerical parameters: height, width, thickness, concrete mixture, hydroelectric turbine size, curvature, etc.  After evaluating all the dams, the engineer picks the 100 best and discards the rest.  He then copies each of these dams 100 times.  When copying, the engineer randomly introduces minor differences: say he rolls a die each time he copies a design parameter; if he rolls a six, he then changes that parameter by 1%, flipping a coin to determine if he will increase or decrease the parameter.  Once he has finished copying, he will have 10,000 more dams, most of them very similar to the original 100 but with some small differences.  He then evaluates these 10,000 dams again, picks the best 100, and copies them again, introducing random "errors" in the same way.  After completing this process several thousand times, the engineer has 10,000 dams, all of which perform excellently.  He picks the best of them and thus has an excellent design, without ever doing any real "design" himself.  Note that this engineer need not be conscious of the overall goal--he is just applying a simple algorithm over and over.  Indeed, the engineer need not be conscious of anything at all--his task could be performed automatically and without sentience or intelligence.

An engineer starts with 10,000 different sets of plans for a hydroelectric dam.  His dam must complete two basic tasks: it must hold back a lake with minimal flooding of the surrounding area, and it must maximize power generation.  The intrinsic worth of a dam is determined by how well it completes these tasks; a dam which produces 100 kW of electricity while only raising water levels 2 feet is superior to one which produces 10 kW of electricity while raising water levels 5 feet.  In our simplified example, let us assume that the design of a dam is based on just a few numerical parameters: height, width, thickness, concrete mixture, hydroelectric turbine size, curvature, etc.  After evaluating all the dams, the engineer picks the 100 best and discards the rest.  He then copies each of these dams 100 times.  When copying, the engineer randomly introduces minor differences: say he rolls a die each time he copies a design parameter; if he rolls a six, he then changes that parameter by 1%, flipping a coin to determine if he will increase or decrease the parameter.  Once he has finished copying, he will have 10,000 more dams, most of them very similar to the original 100 but with some small differences.  He then evaluates these 10,000 dams again, picks the best 100, and copies them again, introducing random "errors" in the same way.  After completing this process several thousand times, the engineer has 10,000 dams, all of which perform excellently.  He picks the best of them and thus has an excellent design, without ever doing any real "design" himself.  Note that this engineer need not be conscious of the overall goal--he is just applying a simple algorithm over and over.  Indeed, the engineer need not be conscious of anything at all--his task could be performed automatically and without sentience or intelligence.  Note also that the final dam may be very different from any of the original dams.

== Local and Non-Local Improvement ==  

== Local and Non-Local Improvement ==