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Evolution Explained January 20, 2009

Posted by Ian in Science.
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In a coming series of posts (I have no idea how many yet) I will attempt to address common misconceptions about the theory of evolution which many people (even those who accept evolution by natural selection) often get wrong in my opinion.  Before I start this set of posts however I would like to briefly explain what the theory of evolution is as context for understanding these explanations.  I will probably refer to this post several times in the future. 

Firstly I need to make the point that I am talking specifically about evolution by natural selection.  The word “evolution” alone is generally synonymous with this but the word does have other meanings in other contexts.  I am not interested in those for the purposes of these posts.


 My Definition

Evolution by natural selection is simply the statistical process by which a set of replicators with variation will tend to optimise fitness within its environment.


 

That’s it.  A fascinating and remarkably powerful idea but that power stems from its implications rather than its complexity.  In fact its simplicity is what makes it truly remarkable because you don’t need anything more to explain what might otherwise seem impossible.

I italicised some terms in that definition above which I will explain a bit further below:

Statistical process 
Evolution is not a “thing” but rather just a statistical observation which can be summarised as:  Those that are more likely to survive are more likely to survive.  This can be further shortened to survival of the fittest which becomes true given enough observations (like any statistical thing).  Note that it does not say anything specific about any one organism or any system at any point in time – it only describes a tendency over time.  For example a less fit organism may survive over a more fit organism in the short term but over time the fittest will tend to out-survive the less fit. 

Replicators
A replicator is anything that can create copies of itself within its environment.

Variation 
Perfect replicators are not subject to evolution by natural selection because there is nothing to distinguish individuals in terms of their relative fitness.  However if there are even tiny variations then this is sufficient for evolution by natural selection to work.

Optimise fitness
Optimisation is the process of maximising (or minimising) something in the context of an environment.  Generally organisms want to maximise their numbers in an environment because this almost always will maximise the probability of long term survival.  Note this is not an explicit or defined goal but simply the logical result of any real system – only those that survive can be considered fit in the first place so survival itself becomes necessary by default. 

Also note that fitness is always relative to the environment so it is heavily influenced by other organisms, available matter and energy, and the characteristics of the organism.  Finally optimisation is rarely with respect to the entire system but rather is defined by the fittest place that the replicator could get to with the current state of the system.  This can often mean that a better version of the replicator is possible but unattainable given the environment and nature of the replicator.

Environment
This term is a very general term that basically refers to everything that influences the existence of the replicator including other replicators (both the same and different to the organism), the matter and energy in the environment, and anything else that might matter to the survival or operation of the replicator.


Conclusion
So having established what evolution by natural selection actually is, I will move onto discussing the misconceptions of evolution in the following posts.

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