Definition of evolution

[studiot]

Is physically passing on the evolved characteristic to a subsequent generation necessary for the change to be classified as evolution?

 

Or is just the appearance of the change itself enough?

 

An does this term only aplly to the first time the change occurs or can it also apply to any instance of this change?

 

For instance if I take two petri dishes of culture and allow (stimulate) identical (evolutionary ?) changes in each and prove that they are transmitted to the next generation by allowing this to happen in one dish, but prevent transmission in the second by killing all the culture or otherwise. Do both instances qualify as being called an evolutionary change?

[pwagen]

Most (if not all) definitions I've seen say evolution is something like "change over time" (simplified), which would mean the second dish would not evolve since there is no change. Practically, I think it would be hard to prevent change in other traits than the ones you're killing off, making them change anyway, which would mean they're still evolving. But looked on as a hypothetical question, in which you can actually stop them from changing through generations, this wouldn't be evolution, since there's no change. At least that's my interpretation of this definition.

 

Then again, there are probably countless definitions and interpretations of definitions. I think you'll be hard pressed to get a clear-cut answer.

[studiot]

Actually I didn't say there was no change.

 

I said that there was change in both (in perhaps the same timescale - is timescale necessary or is this another extraneous variable?).

Edited May 28, 2013 by studiot

[D H]

Given the discussion that generated your question, you are (I think) asking about biological evolution. Every technical field has its own set of jargon, words and phrases that have a special meaning in that field. By way of analogy, consider the word "weight". Legally and colloquially, weight is a synonym for mass. Weight in physics is something different. In elementary physics, weight is the force caused by gravitation. In more advanced physics, weight is the net force of everything but gravitation. Regardless of which physics definition of weight one uses, one thing is certain: It is not a synonym for mass.

 

Biological evolution is about how species change. It pertains to life, not pre-life.

[pwagen]

Actually I didn't say there was no change.

 

I said that there was change in both (in perhaps the same timescale - is timescale necessary or is this another extraneous variable?).

Ah yes, I see what you mean now.

Is physically passing on the evolved characteristic to a subsequent generation necessary for the change to be classified as evolution?

This is a misconception, which might skew your whole question actually. Correct me if I'm wrong, but are you saying an individual bacteria evolves a trait over its lifetime, then passes it on to its "kids"? If so, that's not quite right. In larger animals, that would be equal to saying the ancestors of giraffes had to stretch their necks, thus growing longer necks from stretching, which they then pass down.

 

Normally, individuals don't evolve these changes in their lifetime. Instead, it's when they reproduce that their genome quite often have mistakes in them. Most of these are harmless or neutral. Some are fatal to the offspring. And some give the offspring a slightly better chance at surviving. Then there's natural selection, but that's another topic.

 

So basically, you can't "allow change to happen in both groups then stop one group from passing the changes on", as the changes actually happen when they reproduce.

 

Correct me if I'm assuming incorrectly regarding your question.

[EdEarl]

... are you saying an individual bacteria evolves a trait over its lifetime, then passes it on to its "kids"? If so, that's not quite right. In larger animals, that would be equal to saying the ancestors of giraffes had to stretch their necks, thus growing longer necks from stretching, which they then pass down.

Stress releases hormones that can suppress an immune system make an individual susceptible to infection. If the infection is viral, it may result in DNA change (See: http://www.sciencedaily.com/releases/2010/01/100107103621.htm).

 

A person can choose to do things that are stressful. Thus, it is not totally unreasonable that a person may do something to change their DNA, and perhaps alter evolution. Unless I am missing something.

[pwagen]

Stress releases hormones that can suppress an immune system make an individual susceptible to infection. If the infection is viral, it may result in DNA change (See: http://www.sciencedaily.com/releases/2010/01/100107103621.htm).

 

A person can choose to do things that are stressful. Thus, it is not totally unreasonable that a person may do something to change their DNA, and perhaps alter evolution. Unless I am missing something.

Absolutely. And if I'm not mistaken, radiation is another mean of change in a live individual's genome. And it's quite possible studiot meant to induce changes in live individual which are then either passed on or not, in which case I was mistaken. I'll await studiot's clarification before jumping to conclusions.

[studiot]

No I'm trying to nail down the definition of biological evolution, to borrow a phrase from another thread.

 

Here is an example of what I mean.

 

Suppose I have 50 dishes of culture of palin old fashioned staphylococcus aureus and I 'tease' them with doses of methicillin.

 

After a time at least two of the dishes will have developed the strain MRSA that now creates havoc in our hospitals.

 

In dish #1 I allow successive generations of MRSA to develop.

 

I treat dish#2 with a flame thrower so ther are no successive generations.

 

Do I count both dishes as having evolved, even if I subsequently wipe one out?

 

Or do I say that only in the dish I allowed to continue has the Staph Areus evolved?

[D H]

No I'm trying to nail down the definition of biological evolution, to borrow a phrase from another thread.

 

 

Hmm. Do you have me on ignore? I answered that question in post #4.

[studiot]

DH:

Hmm. Do you have me on ignore? I answered that question in post #4

 

D H post#4

Given the discussion that generated your question, you are (I think) asking about biological evolution.

<discussion about physics>

Biological evolution is about how species change. It pertains to life, not pre-life.

 

 

 

Studiot:

No I'm trying to nail down the definition of biological evolution, to borrow a phrase from another thread.

<example explicitly expounded>

 

Why on earth should I be ignoring you, you are doing your best to offer discussion, for which I thank you.

 

I very clearly acknowledged your post#4, repeating your phraseology for just that reason.

 

However nowhere in this thread did I refer to pre-life.

The example I gave refers to some very much alive organisms.

The phrase I borrowed was from Bignose in his thread about advances by 'unknowns', nothing to do with a recent thread about the speed of evolution, which I admit prompted this current thread.

 

Every science, including biology, needs to have logically consistent definitions.

 

I am simply trying to examine (collectively if others will cooperate) the logical implications of what has been said about the definition, coupled with my own research.

 

Everyone is welcome to offer their own material.

 

 

[StringJunky]

In biology, evolution is change in allele frequency over time, where an allele is one form of possible expression of a gene e.g. short or tall. I might well be wrong but I would have thought the flame-throwered sample's evolutionary line would be classed as becoming extinct, not evolved.

 

If you are also thinking about pre-life 'evolution', encompassing the transition from precursor molecules to the first living organisms, this is called abiogenesis.

[studiot]

change in allele frequency over time

 

 

OK so I have two identical petri dishes, containing identical samples of Staph A, with identical evolutionary histories, ie they have both evolved from non methicillin resistant to methicillin resistant.

 

How long do I have to wait before destroying the second one, to say that it too has evolved?

 

A millisecond, an hour, a day, a year?

[StringJunky]

OK so I have two identical petri dishes, containing identical samples of Staph A, with identical evolutionary histories, ie they have both evolved from non methicillin resistant to methicillin resistant.

 

How long do I have to wait before destroying the second one, to say that it too has evolved?

 

A millisecond, an hour, a day, a year?

 

The keyword in that definition is frequency and I don't know what the established consensus is on the minimum percentage required in the sample for it to be said that the population has evolved. you need a someone more knowledgeable than me to chime in to answer that.

[studiot]

The keyword in that definition is frequency and I don't know what the established consensus is on the minimum percentage required in the sample for it to be said that the population has evolved. you need a someone more knowledgeable than me to chime in to answer that.

 

 

 

Thank you for your input, it has different material from that of others.

 

So far I have heard the ideas that (not all yours)

 

1)A change must be involved.

 

2)The change must be genetically transmissible.

 

3)There is a minimum acceptable % of the population that change, regardless? of whether it is permanent.

 

4)The change must take place over some(undefined) timescale.

 

5)It is generally argued that the pre change and post change entity must be 'alive'

 

6) No restriction has so far been placed on the agent (stimulus) of change.

[StringJunky]

5)It is generally argued that the pre change and post change entity must be 'alive'

 

Yes, evolution, biologically, pertains to living things AFAIK.

 

No restriction has so far been placed on the agent (stimulus) of change.

 

Anything that causes a change in an organism's genome may ultimately alter it's species' evolution, if circumstances favour it..

[Delta1212]

No I'm trying to nail down the definition of biological evolution, to borrow a phrase from another thread.

 

Here is an example of what I mean.

 

Suppose I have 50 dishes of culture of palin old fashioned staphylococcus aureus and I 'tease' them with doses of methicillin.

 

After a time at least two of the dishes will have developed the strain MRSA that now creates havoc in our hospitals.

 

In dish #1 I allow successive generations of MRSA to develop.

 

I treat dish#2 with a flame thrower so ther are no successive generations.

 

Do I count both dishes as having evolved, even if I subsequently wipe one out?

 

Or do I say that only in the dish I allowed to continue has the Staph Areus evolved?

The thing is, you already have successive generations built into your scenario for both dishes. The MRSA strain is a different generation from the original, non-resistant one, and it's not a change that will instantly take over the population, which means you've already had to go through several "generations" of the bacteria to get the resistant strain.

 

You can then wipe out the culture and that strain will go extinct, but it did evolve to get to that point, and did it generationally.

[studiot]

The thing is, you already have successive generations built into your scenario for both dishes. The MRSA strain is a different generation from the original, non-resistant one, and it's not a change that will instantly take over the population, which means you've already had to go through several "generations" of the bacteria to get the resistant strain.

 

You can then wipe out the culture and that strain will go extinct, but it did evolve to get to that point, and did it generationally

 

Thank you for confirming my analysis thus far.

[SeriousBug]

The importrant thing is, the bacteria in the culture must reproduce to evolve. Meaning that, after you expose them to meticillin, lets say that one bacteria in the dish managed to produce meticillin resistance. I suppose you can call this one bacteria as "evolved", however to say that the bacteria in the petri dish has evolved, you would need to let it reproduce and take over the previous nonresistant type.

[studiot]

Which begs the question of 'take over' ?

[SeriousBug]

Sorry, I meant the nonresistant ones going extinct(or falling to low numbers, less than the resistant ones) and the resistant ones surviving. I forgot the word for it, I'll edit my message if I do.

Edit: I checked it, and I think succession would be the correct term.

Edited May 29, 2013 by SeriousBug

[studiot]

So you wish to place the restriction that the former population must die out for the change to be considered evolution.

 

Why can both the old and new not coexist?

[D H]

Why can both the old and new not coexist?

 

They can. Darwin's finches, for example. Related: Google the term "ring species".

[studiot]

So are we going to add take over or displace as condition 7 or not ?

[Delta1212]

Ok, let's take this one at a time.

Is physically passing on the evolved characteristic to a subsequent generation necessary for the change to be classified as evolution?

 

New characteristics are caused by mutations in a subsequent generation. Mutation is one element of evolution.

 

Or is just the appearance of the change itself enough?

 

The appearance would be an example of a change in allele frequency of the population, since there is an allele that didn't exist before, so that would meet that definition of evolution, although, again, you won't get this new characteristic cropping up without reproduction

An does this term only aplly to the first time the change occurs or can it also apply to any instance of this change?

 

Any time a change occurs is a mutation.

For instance if I take two petri dishes of culture and allow (stimulate) identical (evolutionary ?) changes in each and prove that they are transmitted to the next generation by allowing this to happen in one dish, but prevent transmission in the second by killing all the culture or otherwise. Do both instances qualify as being called an evolutionary change?

Any new characteristic that pops up would be the result of a mutation, and any environment you set up to select for that mutation and cause a change in the population that would result in the culture evolving. The change would already have been transmitted to a subsequent generation, so you can't really say that you prevented it from being transmitted in one.

 

 

Part of your problem here is that evolution is a process, not an event. Attempting to define it by required parts is difficult because a lot of things can result in evolution.

 

It's like driving. Is pressing the gas pedal driving? What if the car is off? So the car has to be on. What if you're coasting on the highway? So the car has to be moving? If you're stopped at a red light, are you no longer driving? What if you crash into a wall? Are you still driving while the car hits it? What if you don't have your hands on the wheel or foot on the pedal at that moment? What if you take your hands off the wheel and foot off the pedal while on the highway? What about cars that have a manual transmission? Does the clutch constitute an element of driving? Can you not drive automatic cars then, or is it irrelevant?

 

There are a lot of things that contribute to evolution: reproduction, mutation, and death are major elements. Can you pick out one and say, there, when that happens, is it evolution? Well, in the sense that that event contributes to evolution, yes. In the sense that that event defines evolution, no, because there are other things that can happen which also contribute to evolution taking place.

[studiot]

Part of your problem here is that evolution is a process, not an event. Attempting to define it by required parts is difficult because a lot of things can result in evolution.

 

It's like driving. Is pressing the gas pedal driving? What if the car is off? So the car has to be on. What if you're coasting on the highway? So the car has to be moving? If you're stopped at a red light, are you no longer driving? What if you crash into a wall? Are you still driving while the car hits it? What if you don't have your hands on the wheel or foot on the pedal at that moment? What if you take your hands off the wheel and foot off the pedal while on the highway? What about cars that have a manual transmission? Does the clutch constitute an element of driving? Can you not drive automatic cars then, or is it irrelevant?

 

 

 

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.