Changes

== 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.  In the language of the above example, let us say that one of the dams would be much improved if the curvature were increased by 10%, but would be worsened considerably if the curvature was 3 to 7% higher.  Since curvature can only change by 1% at a time, and a regime of "bad" curvature lies between the current regime and the regime of "good" curvature, the dam will never reach the "good" regime.  Thus, in order for a large change to take place over several generations, it must be beneficial (or at least not significantly harmful) at ''each'' generation.  Again returning to the peacock, it might be an overall advantage to have a very short tail or no tail at all, since predators would be easy to avoid.  However, since a ''slightly'' shorter tail gives little help in avoiding predators and also is much less attractive to females, short tails are unlikely to come about.

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.

* [[Theory of evolution through natural selection]]

In the language of the above example, let us say that one of the plans would be much improved if the curvature were increased by 10%, but would be worsened considerably if the curvature was 3 to 7% higher.  Since curvature can only change by 1% at a time, and a regime of "bad" curvature lies between the current regime and the regime of "good" curvature, the dam will never reach the "good" regime.  Thus, in order for a large change to take place over several generations, it must be beneficial (or at least not significantly harmful) at ''each'' generation.

 

== Natural selection and evolution ==

== Natural selection and evolution ==