Perplexing evolutionary notion

[Dory]

http://answers.yahoo.com/question/index ... 941AAAdUPY

So this guy asks "Why is it said that evolution acts on phenotypes and not genotypes?"

He gets 2 answers, each slightly varied, but none of them make a lot of sense to me:

Answer 1:

Natural selection acts on phenotypes not genotypes because it is what you look-like/can do that affects how well you survive. Having a gene that doesn't affect you phenotype (look/function) doesn't affect your ability to survive so natural selection doesn't act on it.

Answer 2:

Evolution acts on phenotypes by its effect through natural selection. A mutation that prevents the formation of a digestive enzyme means that the organism unlucky enough to have it would starve- the mutation is eliminated from gene pool. An bright orange deer would not survive long in the wild because its color would make it an easy target for predators. The mutation that caused such a phenotype would also be quickly eliminated from the genet pool.

And mind you the second poster seems like an expert with 40 years experience of teaching biology.

However, it doesn't make a lot of sense to me. Think about it, can't natural selection act on something that isn't seen (like a better immune system) and evolution can spur from that, without a change in phenotype? Yes it can, if you ask me. This, in my mind, nullifies the two posters above.

[AnInconvenientScotsman]

http://answers.yahoo.com/question/index ... 941AAAdUPY

So this guy asks "Why is it said that evolution acts on phenotypes and not genotypes?"

He gets 2 answers, each slightly varied, but none of them make a lot of sense to me:

Answer 1:

Natural selection acts on phenotypes not genotypes because it is what you look-like/can do that affects how well you survive. Having a gene that doesn't affect you phenotype (look/function) doesn't affect your ability to survive so natural selection doesn't act on it.

Answer 2:

Evolution acts on phenotypes by its effect through natural selection. A mutation that prevents the formation of a digestive enzyme means that the organism unlucky enough to have it would starve- the mutation is eliminated from gene pool. An bright orange deer would not survive long in the wild because its color would make it an easy target for predators. The mutation that caused such a phenotype would also be quickly eliminated from the genet pool.

And mind you the second poster seems like an expert with 40 years experience of teaching biology.

However, it doesn't make a lot of sense to me. Think about it, can't natural selection act on something that isn't seen (like a better immune system) and evolution can spur from that, without a change in phenotype? Yes it can, if you ask me. This, in my mind, nullifies the two posters above.

IIRC the immune system is part of the phenotype - any observable expression of an organism's genes is.

[Dory]

http://answers.yahoo.com/question/index ... 941AAAdUPY

So this guy asks "Why is it said that evolution acts on phenotypes and not genotypes?"

He gets 2 answers, each slightly varied, but none of them make a lot of sense to me:

Answer 1:

Natural selection acts on phenotypes not genotypes because it is what you look-like/can do that affects how well you survive. Having a gene that doesn't affect you phenotype (look/function) doesn't affect your ability to survive so natural selection doesn't act on it.

Answer 2:

Evolution acts on phenotypes by its effect through natural selection. A mutation that prevents the formation of a digestive enzyme means that the organism unlucky enough to have it would starve- the mutation is eliminated from gene pool. An bright orange deer would not survive long in the wild because its color would make it an easy target for predators. The mutation that caused such a phenotype would also be quickly eliminated from the genet pool.

And mind you the second poster seems like an expert with 40 years experience of teaching biology.

However, it doesn't make a lot of sense to me. Think about it, can't natural selection act on something that isn't seen (like a better immune system) and evolution can spur from that, without a change in phenotype? Yes it can, if you ask me. This, in my mind, nullifies the two posters above.

IIRC the immune system is part of the phenotype - any observable expression of an organism's genes is.

So there are no examples we can't see that improves the ability of the organism to survive?
\

[Feck]

It's not always about what we can see , phenotype is not just an obvious visual thing ,it can be a lot more subtle like the change in one aminoacid may make a slight change to the tertiary structure of a large protein that may make it worse or better at it's function etc.

[julietooo]

http://answers.yahoo.com/question/index ... 941AAAdUPY

So this guy asks "Why is it said that evolution acts on phenotypes and not genotypes?"

He gets 2 answers, each slightly varied, but none of them make a lot of sense to me:

Answer 1:

Natural selection acts on phenotypes not genotypes because it is what you look-like/can do that affects how well you survive. Having a gene that doesn't affect you phenotype (look/function) doesn't affect your ability to survive so natural selection doesn't act on it.

Answer 2:

Evolution acts on phenotypes by its effect through natural selection. A mutation that prevents the formation of a digestive enzyme means that the organism unlucky enough to have it would starve- the mutation is eliminated from gene pool. An bright orange deer would not survive long in the wild because its color would make it an easy target for predators. The mutation that caused such a phenotype would also be quickly eliminated from the genet pool.

And mind you the second poster seems like an expert with 40 years experience of teaching biology.

However, it doesn't make a lot of sense to me. Think about it, can't natural selection act on something that isn't seen (like a better immune system) and evolution can spur from that, without a change in phenotype? Yes it can, if you ask me. This, in my mind, nullifies the two posters above.

IIRC the immune system is part of the phenotype - any observable expression of an organism's genes is.

So there are no examples we can't see that improves the ability of the organism to survive?
\

I think you're misunderstanding 'phenotype' - the phenotype is not necessarily what you can outwardly see - it's just how the genotype is expressed in the organism...to use your example, the mutation that make the immune system better is on the genotype, and changes the phenotype. The phenotype in this case is the more effective immune system.

[Dory]

ah.....gotcha. Thanks guys.

[hackenslash]

The question is misleading. Natural selection operates on the phenotype, but natural selection is NOT evolution, it's merely one factor in evolution. In that regard, the question 'why is it said that evolution acts on phenotype, not genotype' is mis-stated. To see the error, you need to think about what evolution and natural selection are. Evolution is a population phenomenon, while natural selection operates (roughly) at the level of the organism.

[Psi Wavefunction]

Technically, selection acts on the organism. What constitutes this organism isn't always clear, and may vary from taxon to taxon. Also, multi-level selection seems to be the way to go these days, with the organism usually at the most dominant level, and selective force kinda tapering off in either direction from there.

[Tero]

Well, you gotta change the genes and the phenes. It is the chicken and egg thing again.

[Psi Wavefunction]

Well, genes are not the sole units of hereditary information in an organism. There's also epigenetics as well as cytoplasmic/membrane inheritance...

[GenesForLife]

Genomes are, though

Dory, a phenotype is any trait that emerges from the activity of genes, either single genes or in many cases, networks of genes. It does NOT have to be visible, just observable by whatever experimental method catches your fancy.

[JimC]

Genomes are, though

Dory, a phenotype is any trait that emerges from the activity of genes, either single genes or in many cases, networks of genes. It does NOT have to be visible, just observable by whatever experimental method catches your fancy.

It may not even be observable by current technology. All it has to do is make a difference to the interaction of that organism with its environment, and selection can act upon it...

The question is misleading. Natural selection operates on the phenotype, but natural selection is NOT evolution, it's merely one factor in evolution. In that regard, the question 'why is it said that evolution acts on phenotype, not genotype' is mis-stated. To see the error, you need to think about what evolution and natural selection are. Evolution is a population phenomenon, while natural selection operates (roughly) at the level of the organism.

Certainly natural selection is not the only player in evolution, but it remains a key player, in the sense that the vast array of adaptive structures and functions that are a dominant feature of living things are carved by natural selection. Particular details may well come from random chance and genetic drift, but the features of an organism which show survival and reproductive functionality cannot emerge any other way.

Consider a stick insect. Both the elongated body, the nobbly exoskeleton, the colour and the swaying behaviours are beautiful examples of adaptive features directly caused by selective pressure, in this case predation by visually guided predators. However, the exact pattern of the nobbly bits in a given population most probably comes from stochastic, non-selective processes. Run the tape again, and you would have another population of well-adapted stick insects, but with a somewhat different array of exoskeletal protruberances...

[Dory]

Genomes are, though

Dory, a phenotype is any trait that emerges from the activity of genes, either single genes or in many cases, networks of genes. It does NOT have to be visible, just observable by whatever experimental method catches your fancy.

Woah, don't answer so soon. I hardly got to finish the question!

[Psi Wavefunction]

Genomes are, though

Dory, a phenotype is any trait that emerges from the activity of genes, either single genes or in many cases, networks of genes. It does NOT have to be visible, just observable by whatever experimental method catches your fancy.

It may not even be observable by current technology. All it has to do is make a difference to the interaction of that organism with its environment, and selection can act upon it...

The question is misleading. Natural selection operates on the phenotype, but natural selection is NOT evolution, it's merely one factor in evolution. In that regard, the question 'why is it said that evolution acts on phenotype, not genotype' is mis-stated. To see the error, you need to think about what evolution and natural selection are. Evolution is a population phenomenon, while natural selection operates (roughly) at the level of the organism.

Certainly natural selection is not the only player in evolution, but it remains a key player, in the sense that the vast array of adaptive structures and functions that are a dominant feature of living things are carved by natural selection. Particular details may well come from random chance and genetic drift, but the features of an organism which show survival and reproductive functionality cannot emerge any other way.

Consider a stick insect. Both the elongated body, the nobbly exoskeleton, the colour and the swaying behaviours are beautiful examples of adaptive features directly caused by selective pressure, in this case predation by visually guided predators. However, the exact pattern of the nobbly bits in a given population most probably comes from stochastic, non-selective processes. Run the tape again, and you would have another population of well-adapted stick insects, but with a somewhat different array of exoskeletal protruberances...

Oh JimC... we could have a vicious debate about this Incidentally, likely will end up doing PhD with a fairly famous proponent of the importance of non-adaptive evolutionary mechanisms. Just an FYI to everyone: there are multiple definitively different frameworks in evolutionary biology, it's not one theory. Though we do all agree it happened – but that's about it

Genomes are, though

Nope, genomes are not the only heritable system in the cell*. Very few people think about non-genomic inheritance though, as most people focus on large multicellular things where the effects of cellular inheritance are much less dramatic. I propose that it may be a very significant phenomenon in microbial (unicellular) evolution, however, and insist it is worth investigating. Writing that into my NSF research proposal anyway :twisted:

*Sorry, I get a bit twitchy when people get carried away with genome = organism (codes for, whatever) fallacy...

[JimC]

Psi Wavefunction wrote:

Oh JimC... we could have a vicious debate about this Incidentally, likely will end up doing PhD with a fairly famous proponent of the importance of non-adaptive evolutionary mechanisms. Just an FYI to everyone: there are multiple definitively different frameworks in evolutionary biology, it's not one theory. Though we do all agree it happened – but that's about it

The real debate is not whether there are other mechanisms than natural selection which are important factors in the evolutionary history of life on Earth. Only a straw-man uber adaptationist (non-existent, in reality...) would go down that path... Many aspects of the tree of life are down to genetic drift and other mechanisms...

Weirdly, there seems to be a question as to whether whether selection has any place at all. There seems to be an incredible pressure to down-play the role of selection to a bit-player in the theatre of evolution...

Absolutely absurd, of course, when the interesting adaptive features of living things are precisely the features that an "Intelligent Design" proponent would seize on as god's handiwork...

Or would you put the features of a stick insect I described earlier down to non-selective processes?