Changes

==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.  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 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.

==Role in Life Sciences==

==Role in Life Sciences==

Here is an example of how an engineer might use an algorithm that is analogous to the combination of mutation and natural selection in the evolution of organisms.

Here is an example of how an engineer might use an algorithm that is analogous to the combination of mutation and natural selection in the evolution of organisms.

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.

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 plans, the engineer picks the 100 best and discards the rest.  He then copies each of these plans 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.

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 plans, the engineer picks the 100 best and discards the rest.  He then copies each of these plans 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 plans, most of them very similar to the original 100 but with some small differences.  He then evaluates these 10,000 plans 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 plans, all of which perform excellently.  He picks the best of them and thus has an excellent design, without ever doing any real "design" himself.

Once he has finished copying, he will have 10,000 more plans, most of them very similar to the original 100 but with some small differences.  He then evaluates these 10,000 plans 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 plans, 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 plan may be very different from any of the original plans.

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 plan may be very different from any of the original plans.

==Local and Non-Local Improvement==  

==Local and Non-Local Improvement==

The above section illustrates how natural selection and random variation can combine to create improved individuals.  However, it is important to note that there is no long-term planning involved in natural selection.  This means that all changes must be locally beneficial in order to survive.  Essentially, no improvement can take place if a deterioration must take place first.  In order for a change to propagate to future "generations" of individuals, it must not be significantly harmful to ''any'' generation.

The above section illustrates how natural selection and random variation can combine to create improved individuals.  However, it is important to note that there is no long-term planning involved in natural selection.  This means that all changes must be locally beneficial in order to survive.  Essentially, no improvement can take place if a deterioration must take place first.  In order for a change to propagate to future "generations" of individuals, it must not be significantly harmful to ''any'' generation.