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starlarvae

starlarvae's thread hijack (from, "Does evolution follow the scientific method? If so, how?")

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starlarvae    11
[L]ots of things, including random chance, can cause differential reproductive success.

 

Darwinian evolutionary theory does not specify particular causes for differential reproductive success. Anything will do, and quite a few very different things have done at one time or another - from slightly lighter colored bark to rocks falling out of the sky.

 

Right. All kinds of contingencies can be responsible for differential reproductive success. So, what are the necessary and sufficient conditions whereby we attribute the success to natural selection? Or to luck? Or to genetic drift?

 

My point is that the science gets sloppy when we say that we surmise various mechanisms but can't determine which ones contribute how much to any particular outcome. Shouldn't a science be picky about distinguishing one causal agent from another? For example, what are we to make of the notion of "fitness" -- or should we just drop it, since we have no criteria for distinguishing it from reproductive success? Is it just a synonym for reproductive success? Or what about "adaptation"? To say that phenotypes are adapted to their environments is just to say that there are such phenotypes (tip o' the hat to J. Fodor). At the very least, couldn't the theory of evolution clean up its terminology and get rid of extraneous jargon?

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Strange    2478

My point is that the science gets sloppy when we say that we surmise various mechanisms but can't determine which ones contribute how much to any particular outcome.

 

Sometimes we can (with absolute certainty), sometimes we are not sure and sometimes we don't know. You seem the be obsessing on the last.

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starlarvae    11

 

Sometimes we can (with absolute certainty), sometimes we are not sure and sometimes we don't know. You seem the be obsessing on the last.

Science has its limits. No news there. Are you agreeing with me that "the science gets sloppy when we say that we surmise various mechanisms but can't determine which ones contribute how much to any particular outcome."?

 

This comment was made in the context of evolution theory. If we can't discern causality there, then the theory is that much weaker for it. ( I'm not an evolution denier, but I do want the mechanisms to be identified as precisely as possible. )

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Strange    2478

Are you agreeing with me that "the science gets sloppy when we say that we surmise various mechanisms but can't determine which ones contribute how much to any particular outcome."?

 

Of course not. You have given no reason to agree with that.

Edited by Strange

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starlarvae    11

Luck, genetic drift, rocks falling out of the sky, etc, are all perfectly good mechanisms of natural selection. They fit into standard Darwinian theory smoothly and easily.

 

If we can't discern causality there, then the theory is that much weaker for it How so? As no particular cause is implied by the theory, and root causes of differential reproductive success are often obscure and complex, being able to pin down a specific cause for a specific example is hardly to be expected in general.

 

If luck and falling rocks are perfectly good mechanisms of natural selection, then we should try to correct the widespread misunderstanding that natural selection has to do with the particulars of phenotypes and the fitness contributed to them by their various traits.

 

 

If the theory doesn't imply particular causes, then it's not much of a scientific theory. That is, it's merely descriptive, but not explanatory.

 

 

 

 

Edited by starlarvae

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Strange    2478

If luck and falling rocks are perfectly good mechanisms of natural selection, then we should try to correct the widespread misunderstanding that natural selection has to do with the particulars of phenotypes and the fitness contributed to them by their various traits.

 

What makes you think that is a misunderstanding?

 

If the theory doesn't imply particular causes, then it's not much of a scientific theory. That is, it's merely descriptive, but not explanatory.

 

The theory isn't about the causes of natural selection but the effects.

 

I'm not an evolution denier

 

You do a very good impression of one.

Edited by Strange

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starlarvae    11

OK, so there's this phenomenon that occurs, which we call natural selection. It produces effects, which we can observe. These observable effects have to do with gene and trait distributions becoming modified as ancestors give rise to descendants.

But all we're observing is changes in gene and trait distributions as a result of differential reproductive success. And we don't need natural selection to explain that. Given the endless contingencies involved (rocks and luck, and such), it might be useless to try to explain it.

 

Whatever differential reproductive success produces, by way of gene and trait distributions, natural selection can claim credit for it. So natural selection explains nothing.

 

By the way, Strange, truncating my words to create straw men, as you did in your quote, is not a gentlemanly mode of discourse, but a mode of fallacious reasoning.

Edited by starlarvae
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Strange    2478

By the way, Strange, truncating my words to create straw men, as you did in your quote, is not a gentlemanly mode of discourse, but a mode of fallacious reasoning.

 

I was concentrating on the relevant points. I have restored the full text. Although I don't see it makes any difference.

Whatever differential reproductive success produces, by way of gene and trait distributions, natural selection can claim credit for it. So natural selection explains nothing.

 

Differential reproductive success is natural selection. (Or vice versa, if you prefer.)

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starlarvae    11
Differential reproductive success is natural selection. (Or vice versa, if you prefer.)

 

That's where I figured you'd end up.

 

If the two terms are equivalent, then we can drop "natural selection" from our vocabulary, and we'll be none the poorer for it. Nor will evolution theory be any the poorer. If we want to be scientific, then "Differential reproductive success" has to be the preferred term, because it's empirical. We can measure it. "Natural selection" is not only superfluous, but "selection" is a lousy word in this context, because it suggests deliberate agency.

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starlarvae    11

 

No, these are aspects are stochastic events that contrast with natural selection. The latter is specifically tied to differential reproductive success under given conditions. I.e. selective forces act on a given gene pool and shapes the resulting frequency.

 

Why doesn't a falling rock, which kills some members of the local population of some given species, qualify as a "selective force" if it acts on a given gene pool and shapes the resulting frequency?

 

Why exclude "stochastic events" from the list of nature's selective forces? Would a forest fire be a stochastic event? How about a flood, or a drought, or an epidemic?

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Strange    2478

Why doesn't a falling rock, which kills some members of the local population of some given species, qualify as a "selective force" if it acts on a given gene pool and shapes the resulting frequency?

 

If it happens rarely (e.g. the number of people killed by falling rocks) then it will have no selective effect.

 

But if the population lived in an environment where falling rocks killed a significant number of individuals, across the population as a whole, then it could be a selective pressure. Individuals with keener hearing, thicker skulls, eyes nearer the top of their head, faster reactions, etc. might be selected for. Delicate, slower moving individuals would tend to be eliminated.

 

Would a forest fire be a stochastic event? How about a flood, or a drought, or an epidemic?

 

Many plants (e.g. California redwoods) depend on forest fires to propagate. There are plants and animals that have adapted to regular drought. So yes, these "random" events (which actually tend to be fairly periodic) can drive evolution.

 

Can't think of any related to epidemics. Although pandemic diseases can be significant. For example, the development of sickle cell and similar disorders as a response to malaria.

Actually, thinking about it some more, without epidemics, our immune system probably wouldn't have evolved the way it has.

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CharonY    1604

 

Why doesn't a falling rock, which kills some members of the local population of some given species, qualify as a "selective force" if it acts on a given gene pool and shapes the resulting frequency?

 

Why exclude "stochastic events" from the list of nature's selective forces? Would a forest fire be a stochastic event? How about a flood, or a drought, or an epidemic?

 

The example was provided in the context of random effects, such as drift and luck). Which means that all individuals were equally likely to be eliminated. But of course in Strange's example it is not a stochastic event anymore, as now there are individuals that are less likely to die from rock fall.

 

To summarize, a stochastic event in this context is essentially anything affecting the gene pool regardless of its composition. If there are differential reproductive success due to events (such as disease or antibiotics resistance) they are not considered random anymore, as they shape the gene pool in a specific manner.

 

Also note that phenotypes generally do not arise as a response to something. Mutations leading to sickle cell arise with or without malaria. However, their frequency in the population are affected by it.

Edited by CharonY

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starlarvae    11

You seem to think the existence of some kinds of selection events excludes others. Why? For example: How does the occasional asteroid killing everything on land over 40 pounds prevent an incremental improvement in reproductive survival odds via camouflage, in between asteroids?

 

And yet it has explained so much. How do you explain that?

 

 

The terminology is confusing. I want to understand how evolution works. That will require teasing apart cause and effect, or rather the multiplicity of putative causes, when it comes to determining phenotypes.

 

The effect we need to explain is gene and trait distributions in descendant generations. I distinguish gene and trait to accommodate heritable epigenetic effects, which allow given genes to produce variant phenotypic traits, which then presumably can, in various ways, influence reproductive success.

 

It seems that gene and trait distributions can be influenced by almost anything, but maybe we can attribute the distributions to these general categories of causes: Natural selection, genetic drift, epigenetic (quasi-Lamarckian) effects, bad luck and good luck.

 

I suppose that these mechanisms can interact in various ways and to varying degrees and in nature would be pretty much impossible to tease apart.

 

Which makes me wonder what justifies the notion of natural selection.

Can somebody provide a clear definition of natural selection? Here's what wikipedia says,

 

"Natural selection is the gradual process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution."

 

The problem with this definition is the phrase, "as a function of," because if we observe differential reproductive success, and the resulting gene and trait distributions, then how do we determine what exactly the differential reproductive success is a function of? How do we justify saying that it is a function of "the effect of inherited traits" rather than something else, when so many possible influences can contribute to outcomes?

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Ophiolite    1811

 

I suppose that these mechanisms can interact in various ways and to varying degrees and in nature would be pretty much impossible to tease apart.

I am bemused that you would think this. You appear to have some knowledge of evolution - at least you have some of the vocabulary - yet you are unaware of the many instances in the literature where the causes of particular changes have been tied to the particulars of the environment. I begin with three examples that are so well known I decline to provide citations for them:

1. The Galapagos finches.

2. The moths of the English Midlands.

3. Dwarfism in originally large animals confined to islands.

 

Here are three examples, pulled arbitrarily from the literature, that further demonstrate the falsity of your supposition.

1. Linkage of stout spines on gastropod shells to presence of predatory fishes that feed upon gastropods. Here.

2. Turnover of ammonite species correlating with regressive/transgressive events in the Jurassic. Here.

3. The irreversible loss of olfactory sensitivity in domesticated pigs. Here.

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MonDie    133

...

But all we're observing is changes in gene and trait distributions as a result of differential reproductive success. And we don't need natural selection to explain that. Given the endless contingencies involved (rocks and luck, and such), it might be useless to try to explain it.

 

Whatever differential reproductive success produces, by way of gene and trait distributions, natural selection can claim credit for it. So natural selection explains nothing.

 

...

 

The null hypothesis is that survival is random. Then allele frequencies wouldn't change in a sufficiently large population. Natural selection explains why allele frequencies do change in sufficiently large populations, and why different changes occur in isolated populations.

 

 

 

...

 

If we want to be scientific, then "Differential reproductive success" has to be the preferred term, because it's empirical. We can measure it. "Natural selection" is not only superfluous, but "selection" is a lousy word in this context, because it suggests deliberate agency.

 

Prepare separate cultures or populations. Expose the experimental group to the mechanism of selection.

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starlarvae    11

 

 

No, because that completely misses the point: favourable traits are selected.

 

What makes the traits favorable, other than their being selected?

 

This is a longstanding criticism of natural selection theory: It is a tautology, as in

 

"What gets selected?"

 

"Favorable traits."

 

"What makes a trait favorable?"

 

"It's one that gets selected."

 

BTW, what qualifies as a trait? A fingernail? A finger? A hand? An arm?

The concept of trait is completely arbitrary.

I begin with three examples that are so well known I decline to provide citations for them:

1. The Galapagos finches.

2. The moths of the English Midlands.

3. Dwarfism in originally large animals confined to islands.

 

Here are three examples, pulled arbitrarily from the literature, that further demonstrate the falsity of your supposition.

1. Linkage of stout spines on gastropod shells to presence of predatory fishes that feed upon gastropods. Here.

2. Turnover of ammonite species correlating with regressive/transgressive events in the Jurassic. Here.

3. The irreversible loss of olfactory sensitivity in domesticated pigs. Here.

I'm not sure what this list proves, if anything.

The finches descended from a common ancestral population on the mainland. Members of that population would have varied phenotypically. When the birds went to the islands, they just ended up wherever they found suitable accommodations, as far as edible food and whatever else they found to be agreeable. Shorter beaks took up residence here and longer beaks there. The peppered moths apparently are largely nocturnal, so the coloration/camouflage story doesn't carry much weight. At least some of the widely circulated photos of moths on light and dark trees were staged, and meant for illustrative purposes only. The gastropod shell research is interesting, but no more instructive than research into any other predator / prey relationship. Differential reproductive success can tune the piano, but it can't compose the melody.

 

 

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Strange    2478

I'm not an evolution denier

 

I was willing to give you the benefit of the doubt but ...

 

This is a longstanding criticism of natural selection theory: It is a tautology

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delboy    29

 

This is a longstanding criticism of natural selection theory: It is a tautology, as in

 

"What gets selected?"

 

"Favorable traits."

 

"What makes a trait favorable?"

 

"It's one that gets selected."

 

 

 

Surely not a problem with the theory, just the language. How about:

 

What do organisms have?

 

Traits.

 

What happens?

 

Some get selected. Those could then be defined as favourable traits.

 

BTW, what qualifies as a trait? A fingernail? A finger? A hand? An arm?

The concept of trait is completely arbitrary.

 

 

Anything within the phenotype.

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Delta1212    894

 

What makes the traits favorable, other than their being selected?

 

This is a longstanding criticism of natural selection theory: It is a tautology, as in

 

"What gets selected?"

 

"Favorable traits."

 

"What makes a trait favorable?"

 

"It's one that gets selected."

 

 

That's not a criticism, it's a feature. It actually boggles my mind that something so tautologically simple as that isn't understood by some people, although I guess I now see that even understanding this fact doesn't really seem to aid comprehension.

 

There will be more copies of things that make more copies of themselves. That's how natural selection works. Things that are better at copying themselves will gradually increase in number over time in comparison to things that are not as good at copying themselves. How do you define whether something is good at copying itself? By how many copies it successfully produces.

 

Throw in variation among all of the copying and this inevitably leads to an accumulation of traits that that make things into better self-copiers, because eventually the majority will always be made up of whatever made the most copies of itself.

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starlarvae    11

 

Surely not a problem with the theory, just the language. How about:

 

What do organisms have?

 

Traits.

 

What happens?

 

Some get selected. Those could then be defined as favourable traits.

 

 

Anything within the phenotype.

 

That's still part of the tautology problem. First they're "selected," and then they are dubbed "favorable," after the fact, for having been selected. Is there any distinction to be drawn between selected traits and favorable traits? If not, then let's drop the favorable business and just call them selected traits, because that's the more empirical term. We can count noses and talk about what got selected. "Favorable" just means selected.

If a trait is anything within the phenotype, then a complex organism is made up of an astronomical number of traits. How in the world can we determine in that crow in the tree which of her traits were selected and which just came along for the ride? was the beak selected? or the beak plus the nerves and muscles that move it? or all that plus the geometry of the skull that supports the beak? or the whole bird?

 

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MonDie    133

...

 

BTW, what qualifies as a trait? A fingernail? A finger? A hand? An arm?

The concept of trait is completely arbitrary.

...

 

A trait is usually some manifestation of an allele. For example, purple petals and white petals are two possible traits for pea plant petal color, and they result from different alleles at the same locus.

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Strange    2478

That's still part of the tautology problem. First they're "selected," and then they are dubbed "favorable," after the fact, for having been selected.

 

And that's a problem because ... ?

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Essay    89

How in the world can we determine in that crow in the tree which of her traits were selected and which just came along for the ride?

 

Those hard-to-define, or arbitrary, and astronomically-large number of traits are all “along for the ride” as well as all being subject to ‘selection pressures’ at any given time. It might be a lot of pressure or a little bit or none, or it might operate sporadically to pressure selection, favoring one direction over another, but something will usually be affecting success.

 

And as with any complex phenomenon, it will be nearly impossible to predict specific outcomes by just analyzing the simple parts that make up the whole. But as with most complex phenomena, it is fairly easy to see in retrospect how the simple parts interacted to create the complex whole ...or outcome or phenotype.

 

The Web of Life, by Capra, is a good book for showing how that all works; see also: http://www.scottlondon.com/reviews/capra.html

The Web of Life: A New Scientific Understanding of Living Systems by Fritjof Capra, Anchor Books, Doubleday, New York, 1996.

 

~

Edited by Essay

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starlarvae    11

 

And that's a problem because ... ?

It's akin to circular reasoning, like in Plato's Euthyphro, where, in a nutshell, "piety" is defined as that which pleases the gods. OK, so how do we know which things please the gods? Obviously, it is those things which embody piety. Which is what? That which pleases the gods, of course. And so on.

 

Which traits contribute most to reproductive success (or "adaptation" or "fitness," etc.)? Those which are selected. OK, so how do we know which ones will be selected? Obviously, it is those traits that will contribute most to fitness. But which are those? They are the ones that get selected. And so on.

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Strange    2478

It's akin to circular reasoning

 

You appear to be confusing an informal description of the theory with the theory itself. I guess next you will be attacking "survival of the fittest".

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