Dawkins and the extended phenotype

[twickster]

I’m currently reading Richard Dawkins’s Ancestor’s Tale, and have arrived at the rodents. He uses the opportunity to talk about the beaver as an example of an animal that creates what he calls “extended phenotypes,” which are (as I understand it, and I am not a biologist) expressions of the action of the gene in the external world.

Basically, he’s saying that the phenotype, or external appearance, of the animal [in this case, let’s not even worry about plants or bacteria or whatever] can be considered a secondary byproduct of genetic action, the primary genetic action being protein synthesis. This phenotype is about maximizing reproductive fitness in any of a variety of ways.

That’s all pretty standard stuff.

With the extended phenotype, he’s looking at the actions of the animal in the world outside its body, also with the “goal” (and, yes, I understand that “goal” language is always a little tricky in talking about evolutionary biology) of maximizing reproductive fitness – for instance, by creating shelters. He looks at the specific example of a beaver dam and the resulting lake, and calls the lake – not just the dam – an “extended phenotype.”

Question 1: Am I understanding this right?
Question 2: If a beaver dam is an extended phenotype, I assume a beehive would be as well. Would a spiderweb?
Question 3: How generally accepted is his theory?

(And may I just say here, as a fairly irrelevant aside, that nonfiction books that are not only not footnoted but don’t even have end notes that summarize the main sources of each chapter piss me right the fuck off? I don’t care that your bibliography runs to 327 items if there’s no indication which of those items was read and used – or refuted – for what points.)

TIA, Colibri – or whoever.

[muttrox]

That’s how I understood it also. He basically is saying that you can have a richer view of a gene’s expression if you don’t limit your viewpoint to only the organism, but consider it’s impact on nature and other organisms.

[Quercus]

I haven’t read him (so #1 don’t know if you have it right).
But your description makes sense to me, and (#2) -from my understanding a spiderweb would certainly be in the same category as a beaver dam.

As to #3, I wouldn’t really call the ‘extended phenotype’ concept (as you describe it) a scientific theory. It doesn’t make any predictions that can be tested. And it’s not really saying anything that the current neo-Darwinian model of evolution doesn’t say. It’s really just sort of pointing out what’s important to focus on, or at most slighting shifting definitions, but in a way that only changes the vocabulary, not the explanation. And additionally, the definitions in either case are pretty fuzzy.

So asking whether scientists ‘accept’ it is not going to have a yes/no answer. Most scientists would probably say something like “There’s nothing really there to argue with. In some cases, using that expression might be useful and save some time, but in others it could obscure important issues.”

[twickster]

@Quercus

So asking whether scientists ‘accept’ it is not going to have a yes/no answer. Most scientists would probably say something like “There’s nothing really there to argue with. In some cases, using that expression might be useful and save some time, but in others it could obscure important issues.”

Good point. I’ll remove the word “theory” as not being technically apropos, and rephrase #3 as “is this a way of talking about things that other evolutionary biologists find helpful?”

[Frylock]

By the way, in case you didn’t know OP, Dawkins wrote a whole 'nother book titled The Extended Phenotype.

-FrL-

[twickster]

@Frylock

By the way, in case you didn’t know OP, Dawkins wrote a whole 'nother book titled The Extended Phenotype.

-FrL-

Yeah, he mentions that. (Gotta say that the version of his personality that comes through his writing isn’t one that appeals to me.)

Anyway, I’m still brooding about the lake formed by the beaver dam, and not just the dam, being considered an extended phenotype.

Quoting Dawkins (p. 187):

how can it possibly be right to use the same word, phenotype, on the one hand for a tail of flesh, bone and blood, and on the other for a body of still water, stemmed in a velley by a dam? The answer is that both are manifestations of beaver genes; both have evolved to become better and better at preserving those genes; both are linked to the genes they express by a similar chain of embryological links.

Okay – this is where it stops making sense. I can see the dam functioning as a phenotype, it being the direct creation of the beavers – but the lake itself … well, yeah, apparently the dam is made “in order to” create the lake, the lake providing a watery protection for the den …

Ugh. Maybe.

As I said – are people other than the Great Dawkins Himself persuaded by this?

[dracoi]

I’m not persuaded by anything Dawkins says, but…

Think of it this way: if beavers built dams and ponds didn’t form, there would be one less reason to build dams. Virtually any burrow or nest would be sufficient, especially versions that would take a lot less work to build and maintain.

Or this way: if ponds were the primary breeding ground of some great beaver devouring predator, beavers with dams that created ponds would very quickly be eaten. Thus, you’d expect them to quit building dams or at least build the dams with holes in them.

Either way, natural selection is working on beaver genes based on whether the pond (as an expression of the genes) is helpful or not.

[runcible_spoon]

To continue dracois’s line of reasoning, extending the extended phenotype to include the lake seems reasonable. I think the difference is in what you’re looking at as the criteria for including something in the extended phenotype. If you use ‘things created by the beaver’, the dam looks like a better candidate than the lake - after all, the beaver isn’t directly forming the lake. Instead, I’d use ‘changes the beaver causes in its environment’, because it’s really not important how the change is caused (directly or indirectly) but that it exists, and was a result of some aspect of the beaver’s genotype.

[Smeghead]

I don’t know. Speaking as someone in the field, I don’t think of it as an argument that I need to be persuaded by. I’d describe it more as an interesting way of looking at things that has some validity and may be useful in some situations, but probably not in others. Something to keep in the toolbox rather than a dogma to believe in.

[Darwin_s_Finch]

@runcible_spoon

To continue dracois’s line of reasoning, extending the extended phenotype to include the lake seems reasonable. I think the difference is in what you’re looking at as the criteria for including something in the extended phenotype. If you use ‘things created by the beaver’, the dam looks like a better candidate than the lake - after all, the beaver isn’t directly forming the lake. Instead, I’d use ‘changes the beaver causes in its environment’, because it’s really not important how the change is caused (directly or indirectly) but that it exists, and was a result of some aspect of the beaver’s genotype.

That, however, is far too broad to be useful. By that definition, everything on the planet is the extended phenotype of Homo sapiens, since there are precious few areas that are free from our influence. And, since pretty much everything we have wrought is a function of our brains, which are in turn dictated to a large extent by our genes, well, you can see the road that one is thereby compelled to walk down.

Ultimately, if one is going to put stock in the idea of an extended phenotype, one must consider that the phenotype must be able to be selected upon in some manner, and that selection must (in Dawkins’ view) ultimately express itself upon the gene(s) responsible for the extended phenotype.

The nature of the beaver’s dam, then, can certainly have an effect on the reproductive success of the beaver. The lake itself, however, is an incidental effect of the dam, governed more by factors outside of the organism (or its genes) than within it. The location of the dam, the flow of the stream, the topology of the surrounding land, etc., all affect the form (e.g., size, depth) of the lake more so than the dam or the beavers themselves. And the form of the lake, in turn, has wide-ranging effects on the surrounding ecological communities.

The key point, however, is that as far as the beavers are concerned, wood + mud + water of sufficient depth to offer safety for those within the dam = “good”. Any qualities of the lake beyond that are only incidental to what has actually been selected for with regard to beaver behavior (unless, of course, it can be shown that beavers do build their dams specifically with an eye toward the ecosystem of the resulting lake and environs. However, then we’d have to concede that beaver intelligence is pretty far beyond what we’d normally attribute to rodents, and better than many civil engineers…).

Basically, there’s no way for the lake itself to feed back to the genes of the beaver, therefore it cannot, in my opinion, be viewed as an extension of the beaver’s phenotype.

[twickster]

Thanks for your comments, all – esp. Darwin’s Finch, who, not at all surprisingly, was able to articulate what it was that I was rather confusedly getting stuck on.

And smeghead – “interesting, perhaps, sometimes, but not truly fundamentally useful” sounds about right.

(And dracoi and runcible spoon, thank you also.)

I’m a humanities type – this is so not the way my brain works naturally. I may be back later with an additional “yeah but” or two after I think about this some more.

[ultrafilter]

@twickster

Yeah, he mentions that. (Gotta say that the version of his personality that comes through his writing isn’t one that appeals to me.)

You don’t see that so much in “The Extended Phenotype” or its precursor, “The Selfish Gene”.

[Colibri]

@Darwin_s_Finch

The key point, however, is that as far as the beavers are concerned, wood + mud + water of sufficient depth to offer safety for those within the dam = “good”. Any qualities of the lake beyond that are only incidental to what has actually been selected for with regard to beaver behavior (unless, of course, it can be shown that beavers do build their dams specifically with an eye toward the ecosystem of the resulting lake and environs. However, then we’d have to concede that beaver intelligence is pretty far beyond what we’d normally attribute to rodents, and better than many civil engineers…).

Basically, there’s no way for the lake itself to feed back to the genes of the beaver, therefore it cannot, in my opinion, be viewed as an extension of the beaver’s phenotype.

I’d agree. Lakes of many different shapes and sizes can form behind a beaver’s dam, and all may be equally “good” with respect to allowing the survival of the beaver and hence the selection of its genes. There could be some selective effects of, say, large vs small lakes, but these are probably so nebulous as to be negligible.

[runcible_spoon]

@Colibri

I’d agree. Lakes of many different shapes and sizes can form behind a beaver’s dam, and all may be equally “good” with respect to allowing the survival of the beaver and hence the selection of its genes. There could be some selective effects of, say, large vs small lakes, but these are probably so nebulous as to be negligible.

Hmmm… that’s a good point. How strongly an environmental change affects the selection of the originating species should definitely be kept in mind. I’d argue that something with a negligible effect still part of the extended phenotype, in the same way that, say, the last centimeter of one single hair on my head are still part of my phenotype - but that’s just 'cause I’m a semantic asshole.

As for beavers, well, I just don’t know enough about beaver dam-building to know how extensively the lake plays in natural selection. I could see it being very relevant, if for instance beavers in large bodies of water fare better than in those in smaller - beavers who build big lakes would then do better. But that’s pure speculation on my part.

@Darwin's Finch

That, however, is far too broad to be useful. By that definition, everything on the planet is the extended phenotype of Homo sapiens, since there are precious few areas that are free from our influence. And, since pretty much everything we have wrought is a function of our brains, which are in turn dictated to a large extent by our genes, well, you can see the road that one is thereby compelled to walk down.

I don’t know that there’s one standard for usefulness. For instance, if you’re trying to figure out why a hairless monkey with no muscle tone and shitty survival skills can walk around bits of Alaska without getting et, well, yeah, you’d better be looking at all that environment. Basically, I think you can consider fast-food wrappers and whatnot part of our extended phenotypes, without holding them up as important parts. But if we’re going to have a rigorous definition of extended phenotype (and I’ll acknowledge that that may not even be necessary, since it’s not really a big scientific issue) then we should call even insignificant changes to the environment part of it.

[Half_Man_Half_Wit]

@Darwin_s_Finch

That, however, is far too broad to be useful. By that definition, everything on the planet is the extended phenotype of Homo sapiens, since there are precious few areas that are free from our influence. And, since pretty much everything we have wrought is a function of our brains, which are in turn dictated to a large extent by our genes, well, you can see the road that one is thereby compelled to walk down.

I don’t see how this road leads us to a bad place, though; it seems to me that one could certainly see the effect of humanity on the environment as a part of its extended phenotype – after all, it does manifestly determine our chances of survival, and is at least an indirect result of our genes, by way of culture. Take as an extreme example our wiping ourselves out due to whatever your favourite man-made ecocatastrophe happens to be – I don’t see how this does not mean that culture-creating traits that lead to such results are selected against.

Basically, there’s no way for the lake itself to feed back to the genes of the beaver, therefore it cannot, in my opinion, be viewed as an extension of the beaver’s phenotype.

The existence of the lake does create a genetic feedback, though – it’s a necessary component in enhancing the beaver’s survival chances (through dam building). If the dam building didn’t create a lake, there’d be no point in building a dam at all, it seems to me.

[muttrox]

@Colibri

I’d agree. Lakes of many different shapes and sizes can form behind a beaver’s dam, and all may be equally “good” with respect to allowing the survival of the beaver and hence the selection of its genes. There could be some selective effects of, say, large vs small lakes, but these are probably so nebulous as to be negligible.

My memory of the book is Dawkins believes the characteristics of the lake do have a strong impact on beavers genes. Not all shapes are equally good. Twickster, anyone got a copy handy they can reference the argument?

[Frylock]

@muttrox

My memory of the book is Dawkins believes the characteristics of the lake do have a strong impact on beavers genes. Not all shapes are equally good. Twickster, anyone got a copy handy they can reference the argument?

But is the shape of the lake an expression of the beaver’s genes?

[twickster]

@muttrox

My memory of the book is Dawkins believes the characteristics of the lake do have a strong impact on beavers genes. Not all shapes are equally good. Twickster, anyone got a copy handy they can reference the argument?

Okay – I don’t want to run afoul of our copyright guidelines – or, frankly, do a huge amount of typing – so let me pick and choose here.

After the paragraph I quote above, he goes on as follows (quoting Dawkins, The Ancestor’s Tale, pp. 187 ff.):

The embryological processes by which beaver genes shape beaver tails are not known in detail, but we know the kind of thing that goes on…Genes, in each of the different kinds of cells in a beaver’s tail, behave as if they “know” where they are … There are formidable difficulties in working out how they “know”… but we understand in principle how these difficulties are overcome; and the solutions, like the difficulties themselves, will be of the same general kind when we turn to the development of tiger feet, camel humps and carrot leaves.

They are also of the same general kind in the development of the neuronal and neurochemical mechanisms that drive behavior. Copulatory behavior in beavers is instinctive … In beaver gene pools, genes survived whose phenotypic effects on the brains, the nerves, the muscles, the glands, the bones, and the sense organs of generations of ancestral beavers improved the chances of those very genes passing through those very generations to arrive in the present.

Genes “for” behavior survive in the same kind of way as genes “for” bones, and skin. … Genes are “really” or “directly” responsible only for proteins or other immediate biochemical effects. All other effects, whether on anatomical or behavioral phenotypes, are indirect. But the distinction between direct and indirect is vacuous. What matters in the Darwinian sense is that differences between genes are rendered as differences in phenotypes…

…[definition of phenotype from OED:] “A type of organism distinguishable from others by observable features.” The key word is distinguishable. [goes on to discuss eye color, alleles, etc.] … Gene differences cause phenotypic differences. Gene changes cause phenotypic changes. In Darwinian evolution alleles are selected, vis a vis alternative alleles, by virtue of the differences in their effects on phenotypes.

The beaver’s point is that this comparison between phenotypes can happen anywhere along the chain of causation. All intermediate links along the chain are true phenotypes … There is no such thing as the “ultimate” link in the chain: no final, definitive phenotype. Any consequence of a change in alleles, anywhere in the world, however indirect and however long the chain of causation, is fair game for natural selection, so long as it impinges on the survival of the responsible allele, relative to its rivals.

Now, let’s look at the embryological chain of causation leading to dam-building in beaver. Dam-building bheavior is a complicated stereotypy, built into the brain like a fine-tuned clockwork mechanism… [It] is hard wired in the brain. …

Only beavers have this kind of brain clockwork. … *t must have evolved in slow degrees in ancestral beavers. It evolved because the lakes produced by dams are useful. It is not totally clear what they are useful for, but they must have been useful for the beavers who built them, not just any old beavers. The best guess seems to be that a lake provides a beaver with a safe place to build its lodge, out of reach for most predators, and a safe conduit for transporting food. Whatever the advantage it must be a substantial one …

Like any other useful adaptation, the dam-building clockwork in the brain must have evolved by Darwinian selection of genes. … But which is the phenotype? At which link in the chain of causal links shall we say the genetic difference exerts its effects? The answer, to repeat it, is all links where a difference is seen. [brain “wiring,” cellular chemistry] But also behavior … is a perfectly respectable phenotype. … And, by the same token, the consequences of that behavior are also allowable as phenotypes of genes. What consequences? Dams, of course. And lakes, for these are consequences of dams. Differences between lakes are influenced by differences between dams, just as differences between dams are influenced by differences between behavior patterns, which in turn are consequences of differences between genes. We may say that the characteristics of a dam, or of a lake, are true phenotypic effects of genes, using exactly the logic we use to say that the characteristics of a tail are phenotypic effects of genes.

Conventionally, biologists see the phenotypic effects of a gene as confined within the skin of the individual bearing that gene. The Beaver’s Tale shows that this is unnecessary. The phenotype of a gene, in the ture sense of the word, may extend ouside the skin of the individual. {example: birds’ nests}

[ultrafilter]

@Darwin_s_Finch

Basically, there’s no way for the lake itself to feed back to the genes of the beaver, therefore it cannot, in my opinion, be viewed as an extension of the beaver’s phenotype.

How does the lake differ from old age diseases with a genetic component? There’s no feedback mechanism there either.

[Darwin_s_Finch]

@Half_Man_Half_Wit

I don’t see how this road leads us to a bad place, though; it seems to me that one could certainly see the effect of humanity on the environment as a part of its extended phenotype – after all, it does manifestly determine our chances of survival, and is at least an indirect result of our genes, by way of culture. Take as an extreme example our wiping ourselves out due to whatever your favourite man-made ecocatastrophe happens to be – I don’t see how this does not mean that culture-creating traits that lead to such results are selected against.

It’s not a “bad place”, it’s a useless place when talking about evolution. Every organism ever modifies the environment to some degree. Some of those directly affect the organism (indeed, that’s most likely why they are done). Others are incidental. We pollute beaver lakes with mercury and other toxins, but that’s not because we are genetically pre-disposed to do so. We do it because we don’t care about beavers and their lakes. For a discussion about phenotypes to be of any use in evolutionary discussions, we have to separate the wheat from the chaff; the actual genetically-determined behaviors from the ones that aren’t.

The existence of the lake does create a genetic feedback, though – it’s a necessary component in enhancing the beaver’s survival chances (through dam building). If the dam building didn’t create a lake, there’d be no point in building a dam at all, it seems to me.

As I said, all that matters to the beaver is that the water covering the dam is deep enough. It did not build the dam in hopes of creating a vast lake-based ecosystem. It built it so that its den could be under water, which helps to keep it and its family safe from predators. One’s dam-building abilities can be molded by natural selection, as it is an instinctual behavior. The effects of the dam on the surrounding countryside are the result of physics, not beaver genetics.