Razib has proposed an interesting challenge: Define evolution in ten words or less.
His definition is this:
Differential fitness correlated with heritable variation results in evolution
John Hawks' suggestion is this:
No evolution means equal offspring for everyone!
But both of these focus only on the genetic or selective aspect of evolution (including genetic drift under that rubric). There's a lot more happening in evolution that selection and drift. So here's my suggestion:
Diversity changes through time at all levels of biology.
Why do I not focus on heredity, variation, or selection? Well, if selection was inoperative, say because inheritance was blending not mendelian, or in those cases in real biology where changes occur in the makeup of a population or species due to drift or contingency (after all bolide impacts, while rare, do affect evolution), there would still be evolution.
Diversity can mean the diversity of individual genes, or groups of genes such as haplotype blocks, or cellular epigenetic (i.e., not nucleotidal) structures, or of populations, or of species, or of higher taxa. Nothing remains stable for very long, given enough time. Species split, go extinct, branch out in radiations of diversification due to adaptive novelties or chance. Genes drift to fixation, or duplicate, or get eliminated. Phenotypic variations come and go; some remain in species of a group, while others are replaced or modified. The central message of evolution is this: Things change, and this affects the diversity we see around us at all levels.
There is a lot of talk about "the" units of evolution, and everything from genes, genetic sequences or blocks, cells, organisms, species and ecosystems have been proposed as the basic elements of evolution. Definitions of evolution that focus on genes alone tend to be one-eyed in what they count as interesting. It's not that none of these things are the units of evolution but rather that all of them are. Evolution is what happens when things that are stable cease to be, and what makes things interesting is that they were stable, and now are not.
Late Note: See Rob Skipper at hpb etc. for another version:
Differential heritable variation via stochastic and deterministic forces.
Much closer to my version, and based on RPM's version at evolgen for much the same reasons.
My two cents.
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I'm just a high school teacher and I hesitate to disagree with a philosopher. However, I advocate:
"A change in allele frequency within a population"
I also advocate distinguishing between evolution as fact and evolution as theory. The other definitions seem to address the latter.
And, frankly, it seems misleading to claim that "diversity changes through time at all levels of biology." That is only true if one uses arbitrary lengths of time. Clonal/asexual populations may go through periods in which no measurable evolution (as defined above) is actually taking place, and (even if it is!) there are no detectable morphological/metabolic/behavioral trends observed.
Cheers....Scott Hatfield
Hey, I'm just a philosopher, and I hesitate to disagree with a real teacher, but "allele frequencies" focuses on genetics.
If you observe stasis, then you are using arbitrary periods of time as well. But in clonal populations, you have a change with every mutation in the "population" structure (I scare quote "population" because a population is defined as an interbreeding group, which is not the case per definition with asexuals). Given the rate of mutation, it is almost inevitable there will mutations most of the time. So I doubt that it is true in the case of clonal organisms that they remain static.
Life reproduces; reproduction causes change; change improving reproduction mostly wins.
;-)
"What succeeds, proceeds."
"taxonomies are written by the victors"
"Races go not to the strongest, nor battles to the fastest."
(whoops, that's 11 words, but worth it for riff value)
OK, these aren't very technical. The thing is, doing this with scientific jargon is an exercise in compression, not expression!
"In the kingdom of the blind, the one-eyed man is king"?
"what doesnt kill us, makes us stronger".
I think "Diversity changes .." fits very well with Darwin's view of Evolution as the fact that things are unstable and his theory as one of several possible explanation of Evolution. But I think that we today have such a good understanding of the mechanism behind the changes that the explanation can be added to the definition. I therefore suggest the following "The non random selection of random changes" or to use the full ten words "The non random selection of random changes, causing incremental adjustment".
This lacks a connection to biology but I don't think this is too much of a weakness as evolution also is used in non biological contexts (I'm thinking of evolutionary programming).
What I like about the definition is that it gives a relation between the random process such as mutations or the fact that my parents happened to meet to the non deterministic such as "survival of the fittest" and my parents sex drive (next time I have to pick an example that doesn't give this bad associations) that really is the cornerstone of evolution.
It's true that allele frequencies focus on genetics, but it seems to me that there are very good pedagogical (and, frankly, political) reasons why we should continue to define evolution per se strictly in terms of genetic change. If you're interested, I could elaborate why I think that's the case.
With respect to clonal populations, I didn't mean to imply that no mutations were occurring. Rather, it's my understanding that in sufficiently large populations it's unlikely that the rate of any change approaches the level of statistical significance.
Respectfully submitted...Scott
I'd be interested to hear what your reasons for focussing on allele frequencies are, Scott. Also, can you expand on the point about clonal populations? This doesn't seem intuitive. If mutations occur, and aren't eliminated by selection or drift, it seems that they will persist.
How about: "Differential reproductive success in an imperfectly reproducing population"
You see the trick is to use long words!
Richard Dawkins has proposed "Life results from non-random survival of randomly varying replicators."