Definition of evolution

[Delta1212]

 

I don't have a problem, but I'm glad I stimulated discussion because the discussion has brought out many interesting aspects, and made several think seriously rather than just quibbling.

 

Thank you for your analogy, quite interesting as well as the concept of process rather than event.

 

The bottom line is that good definitions are a pre-requisite for good communication, no matter how difficult that may be. Otherwise discussion so often ends up as a squabble over definition and the meat gets lost in process.

 

I started out with an unclear and wooly idea of biological evolution and have learned a good deal from this thread. Thanks to all those who contributed.

Perhaps rather than "your problem" I should have said "the problem with attempting to define evolution in this particular way."

 

Regardless, the best definition for evolution really is along the lines of "the change in allele frequency in a population over time." Anything that causes that contributes to evolution, but doesn't necessarily encompass evolution. The death of a single individual will (slightly) change the allele frequency of a population because all of that individual's alleles have lost one instance of themselves. The birth of a single individual does the same thing, as each of their alleles now has another instance present in the population.

 

Every birth and death contributes to evolution in this manner, but you can't, for instance, make death a necessary condition for evolution to have taken place, because birth contributes to evolution but doesn't (have to) involve anyone dying.

[studiot]

Anything that causes that contributes to evolution, but doesn't necessarily encompass evolution

 

Not quite sure I understood this sentence, but yes we can agree

 

It's complicated.

 

As a matter of interest to DH, I was thinking of humans, not finches when I asked about coexistance. White people and black people for instance, though I am not sure who evolved from whom, or whether there was 'parallel evolution' or what.

[Arete]

I think there's a few basic definitions missing from the discussion:

 

allele: a particular genetic state at a particular locus or genome - or in other words, a specific genotype.

frequency: the relative proportion of a given allele/alleles in a population of organisms.

population: a group of organisms which share the same pool of alleles.

 

The process of biological evolution happens at the scale of the population, or the meta-population, and can be defined as a change in frequency of alleles over time. The rate of evolution is generally scaled by effective population size (i.e. the number of individuals in your population), the rate of mutation (i.e. how often mutations happen) and the generation time (how ofter individuals within a population are replaced).

 

As mutations occur randomly for the main, even in the absence of any selection, stochastic changes in allele frequency will occur. As such, all populations of organisms will evolve over time. Differential ability of particular alleles to replicate, and thus contribute to the next generation will determine the direction of evolution.

[StringJunky]

I think there's a few basic definitions missing from the discussion:

 

allele: a particular genetic state at a particular locus or genome - or in other words, a specific genotype.

frequency: the relative proportion of a given allele/alleles in a population of organisms.

population: a group of organisms which share the same pool of alleles.

 

The process of biological evolution happens at the scale of the population, or the meta-population, and can be defined as a change in frequency of alleles over time. The rate of evolution is generally scaled by effective population size (i.e. the number of individuals in your population), the rate of mutation (i.e. how often mutations happen) and the generation time (how ofter individuals within a population are replaced).

 

As mutations occur randomly for the main, even in the absence of any selection, stochastic changes in allele frequency will occur. As such, all populations of organisms will evolve over time. Differential ability of particular alleles to replicate, and thus contribute to the next generation will determine the direction of evolution.

 

What proportion of individuals, that express a mutation, are needed for a population to be said to have evolved?

[Arete]

What proportion of individuals, that express a mutation, are needed for a population to be said to have evolved?

 

Any change in relative frequency of alleles over time would be considered "evolution". It comes down to what is practicable/ measurable.

 

To offer an analogy - if the temperature in the room I am sitting in varies whatsoever, it could be said to have gotten warmer/colder. However, if that change was 0.001 degree, it would be unmeasurable - and probably not practical to refer to as a change, athough in absolute/theoretical terms, it would be a change.

 

In the same sense, if I have a plate of 1x10⁶ bacteria with alleles A and B in equal proportions, and a single A individual replicates whist no B individuals replicate, there has been a frequency change, however for all intents and purposes it would remain undetectable/appreciable.

 

Is that clearer?

Edited May 29, 2013 by Arete

[StringJunky]

Any change in relative frequency of alleles over time would be considered "evolution". It comes down to what is practicable/ measurable.

 

To offer an analogy - if the temperature in the room I am sitting in varies whatsoever, it could be said to have gotten warmer/colder. However, if that change was 0.001 degree, it would be unmeasurable - and probably not practical to refer to as a change, athough in absolute/theoretical terms, it would be a change.

 

In the same sense, if I have a plate of 1x10⁶ bacteria with alleles A and B in equal proportions, and a single A individual replicates whist no B individuals replicate, there has been a frequency change, however for all intents and purposes it would remain undetectable/appreciable.

 

Is that clearer?

 

Yes. Thanks.

[studiot]

I think it is interesting at this point to compare other technical uses of the word evolution.

 

(the original use) In nautical terms it refers to the process whereby a sailing ship starts with bare masts and ends up wiht all sails set. ie running through the full range of a process from start to finish.

 

In mathematical terms it refers to the raising to a power.

 

In chemistry terms it refers to the production of a gas during a reaction.

 

In many other disciplines it refers to development/consolidation eg astrogeoscience "the evolution of the solar system".

[Ophiolite]

Definitions are a means of imposing an artificial structure on a continuum of phenomena. In this instance the definitions (and there are more than just "a change in allele frequency over time") were developed for the natural world. It is questionable whether it is even proper to try to apply them rigorously to the artificial scenario you have posited.

 

Serparately, may I ask where you are trying to get to with this?

Edited May 30, 2013 by Ophiolite

[studiot]

Serparately, may I ask where you are trying to get to with this?

 

 

 

Thank you for your thoughts.

 

I take it that you have read the whole thread (it is not very long) and can therefore find answers to the above in my previous responses.

 

I am particularly proud of the fact that many have contributed to this thread and that it has not descended into the all-to-common ya-boo squabble.

[Ophiolite]

I take it that you have read the whole thread (it is not very long) and can therefore find answers to the above in my previous responses.

 

I am particularly proud of the fact that many have contributed to this thread and that it has not descended into the all-to-common ya-boo squabble.

If I had found the answers in what you had written I would not have asked you where you were going with this? Would you please clarify.

 

I'm not proud of the fact that I find your dismissal of my query offhand and rude. And your throw away line at the end seems - when I wear my paranoia hat - implicitly critical of me for even asking the question. I hope your reply will consign such negative thinking to the waste basket.

[studiot]

Ophiolite, no rudeness was intended so please do not take offence.

 

"Where are you going with this?"

 

Well I am an applied mathematician, not a biologist and I was 'told off' in another thread for my interpretation of the word in a 'biological sense'.

 

So I am attempting to explore what is meant by the term, testing for logical inconsistencies as part of the process. Hopefully I will then be able to distinguish between what is and what is not evolution in the biological sense, without committing any logical errors.

 

The last line was not an attack on anything you may have said, or not said. It was an observation that IMHO the participants in this thread have managed to exchange views and information without a slanging match, in a proper discussing manner.

 

Incidentally I am suprised you can be so personally critical of soneone whose opening reply to your goodself was

 

"Thank you for your thoughts"

 

Why do you think I would have said this if my objective was a personal attack?

[Ophiolite]

Thank you for your measured response. Please keep in mind that on an internet forum we have only the raw words to deal with. Intonation, pace, volume, emphasis are all absent. Body language is totally invisible. Almost any conversation has some degree of sub-text in it. Ignoring this sub-text can lead to one quite missing the point. Trying to interpret it can lead, as it did in this instance for me, to a gross misinterpretation.

 

You asked me why would I think you had made a personal attack when you opened with the phrase "Thank you for your thoughts". Well, I can produce - and suspect you have seen - many examples of where a formal politeness is used to sarcastically attack. Without the voice and the body language distinguishing the two becomes difficult.

 

I would likely have taken the thank you as genuine were it not for your following sentence:

"I take it that you have read the whole thread (it is not very long) and can therefore find answers to the above in my previous responses."

 

I'll translate that into what I understood you may have intended:

"Well, if you've bothered to read the thread, which you shouldn't find all that difficult because it is short, then you wouldn't need to ask the damn question. I mean my intention is clear. You can see where I am going with it. Read the bloody thing and don't expect me to do all the work."

 

So, I can be personally critical when a person's post is ambiguous and the balance of interpretation is negative. However, in this instance I was not personally critical - I criticised what I thought you may have said and meant - I did not criticise you.

 

i notice at this point I have acquired two Likes for the post. I'm not sure what in particular those were for, but it suggests that my proposed interpretation resonated with at least two members sufficiently to cause them to press the green button.

 

Now, just so we are clear - I'm pleased to hear that I misinterpreted your intent. I believe that means we can now move on, or rather back to topic. In that regard I think what could undermine your efforts here is the presumption that there is a single definition of evolution. Certainly the evolution I think of when wearing a miniature botantist's hat is quite different from the one I wore as a student palaeontologist. Would you accept that it is entirely possible to use differing definitions of evolution without this creating any logical errors?

[studiot]

Would you accept that it is entirely possible to use differing definitions of evolution without this creating any logical errors?

 

 

Yes, of course.

Please expand on both themes and any other you wish to present.