Monday, April 22, 2013

The Top 5 Most Irritating Terms In Evolution Reporting

The first one, "Survival of the Fittest" is the one that is most annoying to me. Why? Because it is often used as a synonym for evolution, but evolution is about so much more!

1. The fittest are not the only ones who survive.
Y'know who survives? The individuals that are sufficient. Sure, some individuals might be more fit than others, and they may have more offspring than others, but many individuals survive (and reproduce) who are certainly not the fittest. And some, who are arguably the fittest, may not survive to reproduce, just due to chance. 

2. The term is not specific about the difference between individuals and populations
While the fittest individuals may be more likely to survive to reproduce, they are not, themselves, evolving. New mutations occur in individuals, and individuals are subject to their environment. Yes, selection acts on individuals, but evolution occurs on populations. This point, that populations evolve, not individuals is crucial, and also wildly interesting because things as simple as the size and structure of populations can affect the efficiency of natural selection. For example, natural selection is more efficient in large populations. Alternatively, deleterious mutations are more likely to drift to high frequency in small populations. So, the fitness of individuals is related to the overall population of which they are a member.

3. Evolution isn't all (or likely even primarily) about survival of the fittest
Survival of the fittest is often used to refer specifically to positive selection acting to favor the reproductive success of individuals with higher fitness in their given environment. This term gives the implication that nearly all of evolution is selection acting on mutations. with a beneficial effect Yes, this happens. But, there are other forces at work; two very important ones are:

1. purifying selection, which acts to remove harmful mutations from the population. An extreme example: if a mutation occurs that makes it impossible for all sperm to swim, that mutation will be eliminated from the population because the affected individual will not produce offspring.
2. (nearly) neutral evolution, whereby mutations with (little or) no effect on the fitness of the individual may drift to high frequency by chance, or because they are linked to mutations with an effect. For example, there are hundreds of thousands of repetitive elements that invasively insert themselves throughout our genome, and generally have no observable effect on fitness, but  continue to accumulate and even become fixed, simply because they do not significantly adversely affect  fitness. 

Whenever I hear "Survival of the Fittest", I am reminded of this quotation:

Think of how stupid the average person is, and realize half of them are stupider than that.

- George Carlin

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