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The standard answer to the question:

what is evolution?

is:

It is a change in allele frequency over time!

I believe a complete definition should encompass the following concepts:

  • mutations
  • copy number variation (CNV)
  • codon usage
  • chromosome numbers
  • maybe some other things...

My questions are:

  1. Would it be worth it to talk about phenotype in a definition of evolution?
  2. What are the alternative definitions that have been proposed?
  3. What is your definition?

Note: I would rather talk about genetic evolution, but if you think it is worth making one definition for genetic and cultural (and some other stuff maybe) evolution, you're free to suggest it!

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Asking the what our individual definitions are is too subjective. Also, are you looking for a definition? Or an explanation. You mention "worth"... worth to who? – user4518 Nov 9 '13 at 16:45
    
@Sancho I think a definition is never objective. It is totally arbitrary to decide what is hidden behind the word "evolution". Therefore, I would have expected several suggestions of definition. I guess a good definition is a definition that fits quite well the everybody sense of what is the boarder of a concept. "Worth" to any individual person willing to answer this question. – Remi.b Nov 9 '13 at 16:54
    
@Sancho Explanation? Explanation of what? I don't think I'm expecting any explanation about the science of evolutionary biology. I guess my question is close to a question of philosophy but I expected better answer by posting here than on philosophy beta. – Remi.b Nov 9 '13 at 16:54
    
@Remi.b Are there "wrong" answers to this question, then? – user4518 Nov 9 '13 at 17:01
    
@Remi.b What is wrong with "It is a change in allele frequency over time". What things does that not include as evolution that it should? What things does it include as evolution that it shouldn't? – user4518 Nov 9 '13 at 17:04
up vote 2 down vote accepted

What is evolution?

In a non-biological sense, evolution means change:

"a process of [...] change"

Biological evolution (seeing as this is Biology stack exchange) then needs to be tweaked to give a biologically specific context. Many textbooks etc. give definitions of evolution and here are a few good ones from across the history of evolutionary biology:

Charles Darwin:

"Descent with modification".

Mark Ridley1:

"Evolution means change, change in the form and behaviour of organisms between generations. ... When members of a population breed and produce the next generation we can imagine a lineage of populations, made up of a series of populations through time. Each population is ancestral to the descendant population in the next generation: a lineage is an ancestor-descendent series of populations. Evolution is then change between generations within a population lineage."

Brian and Deborah Charlesworth2:

"Evolution means cumulative change over time in the characteristics of a population of living organisms. ... All evolutionary changes require initially rare genetic variants to spread among the members of a population, rising to high frequency..."

All of these have a common theme. Biological information is moving through time, descending with a degree of directionality (e.g. parent $\rightarrow$ offspring), and the information is modified with time.

Personally I would define evolution as:

Evolution is a change in gene frequencies, resulting from four mechanisms (mutation, migration, drift, and selection) which can all affect the transmission of heritable genetic information within populations. Evolution has the potential to cause phenotypic change (when genotype affects phenotype) and has the potential to cause both adaptation (microevolution) and divergence (macroevolution).

This definition captures that biological evolution occurs through changes in heritable genetic information, the prerequisites of evolution, the mechanisms of evolution, and what the consequences of those changes can be.

I think it is important to include mutation (and drift, selection, and migration) because these explicitly state how evolution occurs. I don't think it is necessary to include copy number variation, chromosome numbers, or codon usage as they are not central to the process of evolution (though they can be important).

Whilst only the first sentence of my definition is critical, I think it useful to include the latter part (or something of a similar effect) whenever possible as it helps to clarify evolution and it's relevance.


  1. ISBN: 978-1-4051-0345-9

  2. ISBN: 978-0-9815-1942-5

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Nice +1. It is good to have this short review of definitions. I like your definition, I would just note that often when talking about divergence, people are talking about neutral molecular divergence and not phenotypic divergence. Thanks – Remi.b Mar 15 at 14:41

Theoretical biology spans multiple disciplines and the unaccompanied term evolution is defined differently in each:

As such chemical evolution is different from time evolution in physics and many other systems in theoretical biology that "evolve". These do play a role in theoretical biology.

Also, what standard answer to evolution in the field of theoretical biology are you referring to?

I recall learning that an allele as a special[:species:] gene variant, is defined as such as being present in at least one percent of the population. That definition has broadened meanwhile. A definition that has broadened.

Point in case, I don't believe there to be an evolutionary master-framework to (yet) exist, along the lines of desires for a Theory of Everything in physics.

On the other hand, as soon as you cross the boundaries of biological evolution, like let's say in the most primitive of living, biological entities, you are bound to cross over to cultural evolution as well. ( I am no expert on the subject, there are probably other intermittent steps as well). Synergistic effects in the process of evolution may even be considered in Quorum Sensing's most favorite model: Vibrio fischeri.

A simple search on the subject instantly yielded me:

"Evolution of alkaline phosphatase in marine species of Vibrio". J Bacteriol....

In other words: molecular evolution, as being part of the many evolutiony research focuses.

The idea and gross effects of Darwinian evolution are often rather straightforward at first glance. All the little details, that have to be accounted for -with scientific rigor-, as science itself is evolving, are probably where the team-work starts, as do the discussion.

So the only fixture you can count on is team in science.

The introduction to the evolutionary topic at hand, that you would use in an abstract or introduction would depend on the scientific sub-discipline, and would likely already be readily available through peer-publication.

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