Natural Selection vs evolution

[TruthChaser]

I have been wondering a bit lately about the whole evolution talk... there's a significant difference between natural selection and the idea of evolution of higher species (in the way DNA functions).

Anyone willing to discuss?

[Mohit Pandey]

Natural selection is adaptation of living organisms to environment in a better way due to natural favour. For example, crows may eat only species of the beetle which are blue in colour but not the green ones. Thus, the latter are favoured by nature.
Evolution is simply the generation of diversity and the shaping of the diversity by environmental selection. It is a progress from simpler body designs to complex ones. Thus, natural selection is one factor that results in evolution. The other factor is genetic drift.

[freeztar]

Originally Posted by Mohit Pandey

Natural selection is adaptation of living organisms to environment in a better way due to natural favour.

I would say that NS is an indiscriminate process that selects for traits which improve an organism's fitness.

For example, crows may eat only species of the beetle which are blue in colour but not the green ones. Thus, the latter are favoured by nature.

While this is a good example of NS, it's important to note that NS can be driven by internal stimuli as well as external.

Evolution is simply the generation of diversity and the shaping of the diversity by environmental selection.

I quite like the wiki definition for evolution which states:

Originally Posted by wiki

evolution is a change in the inherited traits of a population from one generation to the next.

It is a progress from simpler body designs to complex ones.

Most often this would be true I think, but it does not have to be the case. NS can select for simpler designs according to environmental factors.

Thus, natural selection is one factor that results in evolution. The other factor is genetic drift.

What about speciation? What about mutation?

Take a look at the wiki on evolution, it is very well put together. The panel on the right lists all the mechanisms and processes of evolution and there are lots of links to follow below that.

Evolution - Wikipedia, the free encyclopedia

[Larv]

Originally Posted by Mohit Pandey

Natural selection is adaptation of living organisms to environment in a better way due to natural favour. For example, crows may eat only species of the beetle which are blue in colour but not the green ones. Thus, the latter are favoured by nature.
Evolution is simply the generation of diversity and the shaping of the diversity by environmental selection. It is a progress from simpler body designs to complex ones. Thus, natural selection is one factor that results in evolution. The other factor is genetic drift.

Hi Mohit,

With intentions of furthering this topic, I'll posit three definitions that may be relevant:

1. Natural selection is a reproductive operation. NS may occur when there is differential reproductive success amongst individuals of a population.

2. Random genetic drift is consequence on reduced population size. Genetic drift may occur when a population size becomes small enough to allow for a redistribution of its alleles.

3. Evolution is an operation of changing allele frequencies. Evolution occurs when there is a change in allele frequencies from one generation to the next.

Items #1 and #2 can cause item #3. But there are three other items to consider that may cause evolution:

a. Mutations of genes resulting in fixable alleles.

b. Gene flow, in which fixable alleles are either imported or exported from a population.

c. Sexual selection, in which there is differential mating amongst individuals of a population.

Any of these causes or "forces" of evolution can work independently or in combination to produce a redistribution of fixable alleles in a population.

So it comes down to fixable alleles that are heritable, and to the generations that fix them. Some people say there is something else at work in evolution—"homoplasy"—which pertains to phenotypical traits, heritable or otherwise, and not necessarily to the inheritance of fixable alleles. I am not a believer in homoplasy, or in other explanations of evolution that somehow evade the principle of heritability.

How 'bout you?

—Larv

[freeztar]

Originally Posted by Larv

With intentions of furthering this topic, I'll posit three definitions that may be relevant:

1. Natural selection is a reproductive operation. NS may occur when there is differential reproductive success amongst individuals of a population.

2. Random genetic drift is consequence on reduced population size. Genetic drift may occur when a population size becomes small enough to allow for a redistribution of its alleles.

3. Evolution is an operation of changing allele frequencies. Evolution occurs when there is a change in allele frequencies from one generation to the next.

Items #1 and #2 can cause item #3. But there are three other items to consider that may cause evolution:

a. Mutations of genes resulting in fixable alleles.

b. Gene flow, in which fixable alleles are either imported or exported from a population.

c. Sexual selection, in which there is differential mating amongst individuals of a population.

Any of these causes or "forces" of evolution can work independently or in combination to produce a redistribution of fixable alleles in a population.

So it comes down to fixable alleles that are heritable, and to the generations that fix them. Some people say there is something else at work in evolution—"homoplasy"—which pertains to phenotypical traits, heritable or otherwise, and not necessarily to the inheritance of fixable alleles. I am not a believer in homoplasy, or in other explanations of evolution that somehow evade the principle of heritability.

How 'bout you?

—Larv

First of all, welcome back Larv!
Great post and I'm glad you mentioned alleles.

To address your question:
Homoplasy does not evade hereditary expression. It offers an explanation for why we see similar traits amongst species that do not show a hereditary link.

Environmental factors weigh heavily upon natural selection, which can precipitate similar features, adapted for that environment, amongst all participants. Homoplasy is simply the definition of this occurrence.

[Larv]

Originally Posted by freeztar

To address your question:
Homoplasy does not evade hereditary expression. It offers an explanation for why we see similar traits amongst species that do not show a hereditary link.

Environmental factors weigh heavily upon natural selection, which can precipitate similar features, adapted for that environment, amongst all participants. Homoplasy is simply the definition of this occurrence.

Hi freeztar,

I wish I could accept homoplasy as easily as you do. Every argument in favor of it, in my opinion, has eluded the possibility of genetic predisposition as "an explanation for why we see similar traits amongst species that do not show a hereditary link." Are you familiar with S. J. Gould's concept of "deep homology"? To me, it seems like a better explanation for this so-called "developmental plasticity." I've read West-Eberhard's book on it and find considerable weaknesses in her arguments.

—Larv
.

[Mohit Pandey]

Freeztar--What about speciation? What about mutation?

Oh!yes,u are correct. What about artificial selection by us? e.g. we have, over more than thousand years, cultivated wild cabbage plant as a food plant and generated different varities from it by selection such as kohlrabi, kale.
Aren't we going off-topic as thread is on differences between NS and evolution? But I disagree with TruthChaser as NS is an aspect(factor) of Evolution.
What are your views?

[freeztar]

Originally Posted by Larv

Hi freeztar,

I wish I could accept homoplasy as easily as you do. Every argument in favor of it, in my opinion, has eluded the possibility of genetic predisposition as "an explanation for why we see similar traits amongst species that do not show a hereditary link."

In that case, imho, those arguments are not very good.
Phenotypical variation is genotypical and environmental. When genotypes do not match then we need an explanation for the distant phylogeny amongst species that show similar traits. It can be argued that every organism shares a common ancestor. So homoplasy becomes merely a tool for "drawing a line", a demarcation if you will. So in that sense, I have to agree with you.

Are you familiar with S. J. Gould's concept of "deep homology"? To me, it seems like a better explanation for this so-called "developmental plasticity."

I'm not very familiar with Gould, and in all honesty I've never done much reading of Gould. I'll look into "deep homology" and get back to you on that. It sounds very interesting.

I've read West-Eberhard's book on it and find considerable weaknesses in her arguments.

I've never heard of her, but again, thanks for the reading list. I need to make a trip to the library now.

[freeztar]

Originally Posted by Mohit Pandey

Oh!yes,u are correct. What about artificial selection by us? e.g. we have, over more than thousand years, cultivated wild cabbage plant as a food plant and generated different varities from it by selection such as kohlrabi, kale.

Ah yes! I recommend a wonderful book entitled "The Botany of Desire" which makes the argument that it is not man that has been "artificially selecting" plants, but it is the plants that have been selecting us to further there own evolution. It's a fascinating read and turns the paradigm on its head. Highly recommended!

Aren't we going off-topic as thread is on differences between NS and evolution? But I disagree with TruthChaser as NS is an aspect(factor) of Evolution.

Yes, we are off-topic, but as the discrepancy has been cleared, I feel that it is perfectly appropriate to discuss evolutionary theory in general now.

[Eclogite]

Originally Posted by TruthChaser

I have been wondering a bit lately about the whole evolution talk... there's a significant difference between natural selection and the idea of evolution of higher species (in the way DNA functions).

Would you explain what you believe this significant difference to be. It's quite flown past my head without a sound.