Definition of evolution

@prothero,

prothero;121294 wrote:

No that is not so at all. Darwin knew almost nothing about genes, genetics or alleles.

Sure.

The earliest proponents of electricity knew nothing about electrons.

One definition:

"Evolution describes how living organisms came to be in all our complexity and variety."

Is kind of equivalent to the modern idea of:

"Evolution is changes in allele frequency."

But the second definition is modern scientists talking to one another.

In similar ways - gravity is rarely spoken of as "a relationship between objects based on their proximity, density and mass".

But that means the same thing as "the relative heaviness of stuff".

2 Replies

@memester,

[QUOTE=memester;121295]Aedes apparently does not wish people to notice that he switches forth and back on definition, as necessary for his argument.[/QUOTE] Well in seems Aedes emphasizes genetics as the primary mechanism for evolution and you wish to challenge that. Clearly genetic mutation and the phenotypic variation that results is a major mechanism for evolution. It is not the only mechanism and the mere fact that the frequency of an allele increases or decreases in a population over time does not prove that allele has any survival or procreative effects. So you both I would say have a point. The definition of evolution as Darwin presented it, does not depend directly on genetics only on variation and selection.

1 Reply

@memester,

memester;121286 wrote:

so Evolution is "change in allele frequency, in a population, over time" ?
is that so ?

Maybe not. Let's start with common ground and decide if I was right or not. If we assume that biological changes in a population over time are mediated by genetic determinants (and in this I'll include gene silencing, siRNA, and any other epigenetic phenomenon you like), and we assume that populations are compilations of individuals, then it's a pretty reasonable statement to say that evolution comes down to changes in population-based frequency of genetic determinants over time. And since an allele is simply a genetic variant in a given locus, these are close to synonymous.

But I'm willing to accept a better definition if you've got one.

memester;121286 wrote:

why start off with a different definition , then ?

It's not different, I was starting with that to lead to my allele frequency point.

memester;121286 wrote:

what is behaviour, in your statement, that says plants don't employ it but animals do ?

Let's call it centrally-mediated dynamic activities. By central I mean central to the whole organism, so a nucleus for a single cell, a central nervous system for an animal, and -- well -- what for a plant or a multicellular fungus? By dynamic I mean requiring motion. Plants may grow towards the sun, and change direction if you close one window and open a different one, but that is because of differential rapidity of growth, not a light-seeking behavior. So what centrally-mediated movement do plants have for mate-seeking, mating, eating, defending their young, etc? And a venus fly trap doesn't cut it -- tell me about moss, about junipers, about daisies.

Now your turn. What is behavior, in your question, that says plants DO employ it?

---------- Post added 01-20-2010 at 03:09 PM ----------

prothero;121303 wrote:

The definition of evolution as Darwin presented it, does not depend directly on genetics only on variation and selection.

As Darwin presented it it DOES depend directly on genetics in that he says flat out that there is an unknown mechanism that selection acts on. Darwin did not actually (to my knowledge) discuss variation (i.e. drift), only selection.

1 Reply

@prothero,

prothero;121303 wrote:

The definition of evolution as Darwin presented it, does not depend directly on genetics only on variation and selection.

True, but this highlights why using a 150 year old book - no matter how good it is - as your primary source for the current understanding of the theory is misleading.

Variation does depend on genetics (as far as we can tell).

Darwin didn't rule out things like genetics.

In fact, he speculated that something like genetics was waiting to be discovered.

Seeing as genetics is currently thought to drive evolution - and seeing as changes in alleles is what genetic variation's all about - the two definitions can be looked at as being synonymous, really.

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@memester,

Exactly, Dave.

Of course our understanding of scientific theories change over time. We become more precise with our wording and understanding as we discover the intricaties.

"The change in allele frequency, in a population, over time" and the "The change in species over time", mean the same thing. We just now have a finer understanding of what the thing is that actually changes a species - the alternative DNA sequence, allele. Isn't this right?

1 Reply

@Dave Allen,

Dave Allen;121298 wrote:

"Evolution is changes in allele frequency."
But the second definition is modern scientists talking to one another.".

I respectfully disagree
Evolution results in changes in allele frequency over time but defining evolution in terms of changes in allele frequency is (I would say) not correct. Evolution is a complex process resulting from interaction between behaviors, phenotypes, genotypes, and the enviroment. The definition you use gives emphasis to one factor to the exclusion of all others.
Evolution is the change in species not the change in gene frequency although the two are not independent variables.

Can you give a scientific reference for your definition?

2 Replies

@Aedes,

Aedes;121304 wrote:

Darwin did not actually (to my knowledge) discuss variation (i.e. drift), only selection.

He did speculate on something like Drift.

"The preservation of favourable variations and rejection of injurious variations I call natural selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left as a fluctuating element, as perhaps we see in the species called polymorphic."

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@memester,

I think it is the suggestion that the evolution of species is the same as the evolution of genes to which Memester objects and so do I and so would lots of evolutionary biologists and behavioral scientists.

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@prothero,

prothero;121310 wrote:

I respectfully disagree
Evolution results in changes in allele frequency over time but defining evolution in terms of changes in allele frequency is (I would say) not correct. Evolution is a complex process resulting from interaction between behaviors, phenotypes, genotypes, and the enviroment. The definition you use gives emphasis to one factor to the exclusion of all others.
Evolution is the change in species not the change in gene frequency although the two are not independent variables.

Can you give a scientific reference for your definition?

A body of different causes for the changes in frequency occur - but it is the changes in frequency that supply the differences in variation.

So yes - ecological niches, opportunities and disasters and all sorts of other things might influence those frequencies and drive the success of certain forms and the extinction of others.

But - shorn of that - at brass tacks level - all that is happening is the frequency rate change, and the only aspect that is common to all examples of evolution is the frequency rate change.

It's a very cold and dry exploration of the idea I would agree. I would rather talk about the more interesting peripheral stuff myself.

But it is correct.

Evolution is NOT "change in species". Species are a construction of hindsight and evolution occurs within species (different breeds of dog, for example).

But changes of allele frequency do result in different breeds of dog, changes in species do not.

0 Replies

@prothero,

prothero;121310 wrote:

Evolution results in changes in allele frequency over time but defining evolution in terms of changes in allele frequency is (I would say) not correct.

My point has been that the common denominator of all evolution is alteration in allele frequency, irrespective of the mechanism to get it there.

Now this is certainly an oversimplification, though, because total content of DNA changes as species evolve.

Prothero, I think you're getting into a chicken/egg problem above. Let's take for granted that genetic variations spontaneously arise. It's survival, fecundity, and to some degree statistics and chance that determine how frequent a given variant is in a subsequent generation. So yes, in this regard, the passage of generations alters allele frequency.

But in the end, it's this selfsame change in allele frequency that explains the biological variation of a species over time irrespective of whether human behaviors or natural phenomena influence survival.

1 Reply

@Zetherin,

Zetherin;121309 wrote:

"The change in allele frequency, in a population, over time" and the "The change in species over time", mean the same thing. We just now have a finer understanding of what the thing is that actually changes a species - the alternative DNA sequence, allele. Isn't this right?

Pretty much.

In the same way that a journey of 100 miles can be extrapolated from a single step "a change in species" can be extrapolated from "a change in an allele".

1 Reply

@Dave Allen,

Dave Allen;121316 wrote:

Pretty much.

In the same way that a journey of 100 miles can be extrapolated from a single step "a change in species" can be extrapolated from "a change in an allele".

"a change in allele' is not "a change in allele frequency"
here we go with more changes

---------- Post added 01-20-2010 at 03:41 PM ----------

Aedes;121315 wrote:

My point has been that the common denominator of all evolution is alteration in allele frequency, irrespective of the mechanism to get it there.

if evolution is defined as "change in allele frequency". but not , if not.

---------- Post added 01-20-2010 at 03:44 PM ----------

Aedes;121304 wrote:

Maybe not. Let's start with common ground and decide if I was right or not. If we assume that biological changes in a population over time are mediated by genetic determinants (and in this I'll include gene silencing, siRNA, and any other epigenetic phenomenon you like), and we assume that populations are compilations of individuals, then it's a pretty reasonable statement to say that evolution comes down to changes in population-based frequency of genetic determinants over time. And since an allele is simply a genetic variant in a given locus, these are close to synonymous.

But I'm willing to accept a better definition if you've got one.

we already had one to start with, but you intend to equivocate away from it. It said nothing about alleles, but you now insert that genetic changes mediate ALL changes. And that has not been justified.

1 Reply

@memester,

memester;121318 wrote:

"a change in allele' is not "a change in allele frequency"

Agreed. The latter is a population phenomenon.

memester;121318 wrote:

if evolution is defined as "change in allele frequency". but not , if not.

My argument is that the change in allele frequency is the common denominator of evolution, and this is partly because not all allelic variants produce obvious or even apparent phenotypic changes. However, I would argue that allelic variation also underlies epigenetic phenomena. After all, a siRNA (for instance) is acting on a genetic sequence, an intranuclear hormone receptor that binds directly to a promoter is acting on a genetic sequence, etc.

---------- Post added 01-20-2010 at 03:46 PM ----------

memester;121318 wrote:

we already had one to start with, but you intend to equivocate away from it.

Cut the crap and have a conversation like a grownup.

2 Replies

@Aedes,

Aedes;121324 wrote:

Cut the crap and have a conversation like a grownup.

Don't hold your breath.

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@Aedes,

Aedes;121324 wrote:

Agreed. The latter is a population phenomenon.

My argument is that the change in allele frequency is the common denominator of evolution, and this is partly because not all allelic variants produce obvious or even apparent phenotypic changes. However, I would argue that allelic variation also underlies epigenetic phenomena. After all, a siRNA (for instance) is acting on a genetic sequence, an intranuclear hormone receptor that binds directly to a promoter is acting on a genetic sequence, etc.

---------- Post added 01-20-2010 at 03:46 PM ----------

Cut the crap and have a conversation like a grownup.

You offered a starting definition, and without justification, you move to another. You're demonstrating the childish moves. If you cannot back your words, don't lay the blame on my doorstep.

---------- Post added 01-20-2010 at 03:51 PM ----------

Dave Allen;121326 wrote:

Don't hold your breath.

some people devolve into slimy comment makers once they have been contradicted, eh Dave Allen ?

2 Replies

@memester,

memester;121327 wrote:

some people devolve into slimy comment makers once they have been contradicted, eh Dave Allen ?

Depends on the quality of the contradictor.

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@memester,

this is common ground, and this was offered and accepted

Quote:

'evolution' has to do with changes in populations over time

after that you attempt to alter it without justification.

---------- Post added 01-20-2010 at 03:58 PM ----------

Dave Allen;121331 wrote:

Depends on the quality of the contradictor.

as if you would sense any difference. If is what you are intending to do here, I will lodge a complaint.

1 Reply

@memester,

memester;121332 wrote:

as if you would sense any difference

Sure.

For example Prothero offered a contradicting veiwpoint - and it was clearly for debate rather than pedantry - and I wasn't the least bit slimy in return, I feel.

1 Reply

@Dave Allen,

Dave Allen;121336 wrote:

Sure.

For example Prothero offered a contradicting veiwpoint, and I wasn't the least bit slimy in return, I feel.

so that proves something vis a vis your perspicacity ? it does not. You can continue to bait, and I will continue to show your errors.

Quote:

Sword does not reply to that thread very often

he replied exactly ONE post after you removed this part of the thread that questioned YOU, Aedes.

You need to protect something of yours by removing legitimate posts to elsewhere ?

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@Aedes,

[QUOTE=Aedes;121315] My point has been that the common denominator of all evolution is alteration in allele frequency, irrespective of the mechanism to get it there. [/QUOTE] I guess my objection is not so much to the definition but to the notion that genetic mutation is the only cause or in some populations (especially humans) the major cause of evolution. If the blue eyed blonds of a given population decide to kill off all the brown eyed brown haired members of a population those genes (blond with blue eyes) will increase in the population for example.
[QUOTE=Aedes;121315] Now this is certainly an oversimplification, though, because total content of DNA changes as species evolve. [/QUOTE] I would say it is a vast oversimplification.
[QUOTE=Aedes;121315] Prothero, I think you're getting into a chicken/egg problem above. Let's take for granted that genetic variations spontaneously arise. It's survival, fecundity, and to some degree statistics and chance that determine how frequent a given variant is in a subsequent generation. So yes, in this regard, the passage of generations alters allele frequency. [/QUOTE] I guess I feel emphasizing gene or allele frequency as the definition of evolution inappropriately emphasizes genetics over all other factors involved in the evolutionary process. Unquestionably evolution results in changes in allele frequency over time but it not the only and in some populations not even the major cause. It implies cause and effect when in fact it is only a result. The example of the increasing number of deleterious mutations in populations who have access to better medical care comes to mind.
[QUOTE=Aedes;121315] But in the end, it's this selfsame change in allele frequency that explains the biological variation of a species over time irrespective of whether human behaviors or natural phenomena influence survival. [/QUOTE] I am just trying to make that point that there are a lot more factors involved in the process of evolution than just changes in gene frequency and that change in gene frequency results from factors other than the direct (cause and effect) survival or procreative influence of that gene.

2 Replies

Definition of evolution

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