Sometimes, people email me with good questions. Here’s one.
When I was a kid, my own visualization of evolution was Lamarckism.
But I didn’t know it. In reading Dawkins and others, I know it doesn’t exist. But it seems this article is claiming it does to some extent. Can you comment? I’m curious as to the current consensus as I’ve been reading a lot about genes that can be turned on and passed to offspring. Can you take a look?
This is a fairly common question. Looked at naively, developmental plasticity seems to be Lamarckian — we’re talking about organisms responding with morphological changes to their environment, just like Lamarck’s example of the giraffe stretching its neck. But that’s only the first step; the transmission of a distribution of traits to the next generation is purely Darwinian.
The article that prompted the question is about an experiment in Polypterus, in which the fish were raised in a terrestrial environment, and consequent changes in their limbs and behavior were observed.
A species of fish native to Africa could shed light on the evolutionary process that led fish to move on to dry land. The Dragon fish, Polypterus senegalus is not a normal fish – it has two lungs, and can survive outside of water. In a new eight-month experiment researchers have shown that if a Dragon fish is raised outside of water, the fish changes notably. The fish raised out of water showed differences in their bones and muscles involved in movement not shown in those raised in water.
Fish moved on to dry land and evolved into quadruped vertebrates around 400 million years ago, and it is thought that the Dragon fish is a living demonstration of a phenomenon known as developmental plasticity. This theory states that a creature’s physiology can be changed by environmental factors, and that overtime, these changes are incorporated in to the animal’s genome.
Hans Larsson, of McGill University’s Redpath Museum says that the aim of the experiment was to see the physical changes on Dragon fish that are raised out of the water.
“We wanted to push them in this new environment to see if we could reveal this cryptic variation, and if it works, what does it look like?”
Here’s a video of the animals, illustrating the outcome of the experiment.
Very cool, right? But it doesn’t contradict modern evolutionary theory at all — in fact, it doesn’t require any new concepts, but only the marriage of an understanding of evolution and development. Let’s take those concepts step by step.
Most genetic variation is neutral or nearly so — it has no detectable effect on the phenotype or on viability. Genetic variation can accumulate by drift, but if the differences don’t have any differential effect on survival or reproduction, selection doesn’t care. Most of the variation between humans, for instance, is cryptic: you don’t see it, it doesn’t do much of anything that we can see, but if you look at genes or proteins directly, you can find little differences. Consider blood types, for example: you can’t tell by looking at someone whether they are type A, B, AB, or O, and mostly these don’t seem to matter to the individual (I’m glossing over immunological effects — there is evidence that the blood groups may have arisen in response to malaria infections, for instance).
In order for selection to work, genetic variation has to be visible to it. These cryptic variations only matter if they are made visible to selection. Blood types didn’t have a major effect on people UNTIL blood transfusions became common responses to major injuries…and then having a rare blood type became a detriment. (Again, or until people are otherwise immunologically challenged by parasites with a differential response to blood antigens)
Organisms are plastic: that is, they change their patterns of gene expression in response to the environment. We don’t change blood types, so developmental plasticity is not going to be a major factor there, but other properties of our body are amenable to change. Exercise regularly, your muscles get bigger; eat lots of candy bars, you accumulate fat. There are also genetic differences within these responses. Some people build muscle easily when working out, others are slow to change; some people can eat lots of calories without storing it all as fat, others have metabolisms that shunt most of their intake directly into fat production.
Changing the environment leads to plastic changes in gene expression, which exposes genetic variation to selection. If candy bars were not readily available, the different degrees of fat storage in different people would not be an issue — nobody has the surplus calories, so everybody has the same lean body. You can’t select for the variants either way. Dump a load of candy bars on that population, though, and selectable differences will emerge.
The experiments with Polypterus show something similar. The animals have an inherent capacity for building stronger limbs that is not visible when they are raised continuously in an aquatic environment, but when they are raised in a terrestrial environment, they tend to reinforce bones to a degree that resembles that of fossil fishopods. This is not surprising, any more than it would be surprising if you grew stronger pecs if I forced you to do pushups every day, all day. It also isn’t Lamarckian if you work out and bulk up.
Where it has evolutionary consequences is in the opportunities it opens for selection. If early fish had a propensity for building more robust bones in a terrestrial environment, which allows them to live longer or be more mobile on land, the act of living on land first creates an opportunity for variants that increase terrestrial mobility to be operated on by selection. These variants would be invisible if the animals were always living in the water, after all.
So this is why when we talk about genetic assimilation and say the phenotype comes first, then the genotype arises to consolidate the adaptation, we aren’t talking about anything contrary to standard Darwinian modes of selection. Developmental plasticity creates situations in which otherwise invisible genes can become subject to selection.
I’m just wow walking fish.
All right. So I need a few dozen bichir, a damp terrestrial environment to raise them in, and a fish-friendly race track…
(Seriously: Great post, PZ, and thank you for explaining this so well.)
“Blood types didn’t have a major effect on people UNTIL blood transfusions became common responses to major injuries…and then having a rare blood type became a detriment”
are rare blood types becoming rarer? Is that really a thing?
No, no shift in ABO frequencies that I know of.
That’s an intriguing nuance to add to my understanding of evolution. Thank you.
Don’t know if anyone has actually studied this, but it is doubtful that transfusions have been around for long enough for the selection pressure to have produced any large changes in the gene distributions, and questionable, with likely future advances in transfusion medicine, that the selection pressure will be sustained long enough into the future to have any significant impact on the gene frequencies in the population…
Actually, that out come would be extremely surprising, given what we know about human physiology.
Thanks, PZ.
And I know you’re a fish guy, so I’m not trying to slight you at all, but nonetheless I’m curious as to Jenny Clack’s take on this as well. Obviously she would come at the experiment from a different place.
i’m not assuming she would answer the question posed to you differently, just that she might find other things about the experiment interesting and worthy of comment.
…Wow, why the hell am I so defensive about this?
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Speaking of fish, there was some other question it recently occurred to me I should ask PZ. Now it’s gone. I do, however, reserve the right to pop back in & ask it at any time.
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Finally, as a followup to PZ:
I really get it that developmental plasticity makes genes “visible” to selection. I really do.
And if “genotype” was a population thing, I would totally get, “the phenotype comes first, then the genotype arises to consolidate the adaptation,”.
As it is, I’m not certain I understand it…and I feel rather stupid about that, since I get most of what you say that doesn’t require organic chem.
My tentative understanding is that you’re saying:
“genetic plasticity makes available certain phenotypes, given the correct environmental stimulus/i. In that sense, an appropriate genotype must already exist. However, the important landmarks in evolution happen when a subsequent mutation actually *restricts* previously available plasticity to an environmentally-advantageous phenotype. At that point, what was an environmental possibility becomes a deterministically inherited trait.”
Is that at all correct?
I believe it has been found, however, that some epigenetic changes are heritable, no? This means there are some Lamarckian-like phenomena, after all. E.g., Transgenerational response to nutrition, early life circumstances and longevity. Not really the same as Lamarck’s idea, but an extension of our understanding. Google “heritable methylation” and you’ll get a ton of stuff. I realize I’m wading into deep water even mentioning this in the kingdom of PZ Myers, but I think it’s worth noting. Maybe PZ will want to say something about it.
Please explain.
Hardly. She’d just go on about the changes to the shape of the shoulder-girdle bones at greater length than the video does.
“Not really the same as Lamarck’s idea” = “there are some Lamarckian-like phenomena, after all”?
I really don’t understand that one, cervantes.
I grant you heritable methylation, but I’m not granting Lamarck.
which is a dramatically different point of view than PZ chose to include in his OP.
We’re not in conflict here, are we?
I’m not granting Lamarck either, I said so explicitly. Can you read?
@cervantes.
Yep. I can read.
I can read where you said, “Not really the same as Lamarck’s idea,”
and
I can read where you said, “there are some Lamarckian-like phenomena.”
Which makes your comment incoherent to those of us with actual English skills. I’d recommend against belittling someone’s skills in a language if the substance of their comment is that your comment’s substance on a topic is either
a) self-contradictory (“It’s Lamarck! But it’s not Lamarck!”)
or
b) trivial to the point of WTF (“I know it’s not Lamarck, but isn’t it true that it’s not really Lamarck?”)
and, in any case, would be better to have been silent on that topic altogether (if, say, your point was that epigenetic inheritance exists, and is cool, and raises questions about definitions of “evolution” being base in change in population gene frequencies over time, which requires no mention of Lamarck at all).
Really, talking about facility with the language being employed is, in this case, not reflecting well on you.
@cervantes
I’m interested in PZ’s take on how epigenetic inheritance relates to this as well. Especially transgenerational epigenetic inheritance as it’s directly relevant to how I’m trying to think about myself at the moment (though it is provisional). My understanding is that the things changing as a result of epigenetic changes are adjustable systems composed of interacting gene products. The environmental stimulus alters the system’s state through gene products that involve CpG methylation, histone acetylation, and other things like regulatory RNAs.
Functionally epigenetic modulation is part of how developmental plasticity works from the womb on (global emotional alterations like depression, anxiety tolerance are sill development even later in life!). The precise role in transgenerational developmental plasticity is more murky, but my money is on significant life experiences triggering a system state change that can be reinforced by the environment (anxiety-generating conditions, environmental nutritional availability and even culture).
Well, we’re going to need to define “Lamarckian-like phenomena”, won’t we? The very term suggests that it is not Lamarckism, but something that resembles, but is not identical, to Lamarckism.
So how “like” is “like”?
Consider a hypothetical evolutionary mechanism that involves natural selection of mutations, but the mutations, somehow, are not random. Would we call that “Darwinian-like”? It shares every property of Darwinian evolution except for one, the randomness of the mutations. But the randomness of the mutations is rather central to the Darwinian mechanism, isn’t it?
So what exactly IS Lamarckian Evolution, anyways?
The way I understand that hypothesis is as follows: Inheritance of phenotype arising from use and/or disuse leading to evolutionary change and the production of evolutionary diversity. (It should be noted that when Lamarckism was first proposed, population genetics did not exist, so “gene frequencies in a population”, or even “phenotype frequencies in a population” is not a part of classical Lamarckism.)
The use/disuse part I will allow to be discarded as non-essential (but that’s just my opinion), granting that there are other mechanisms for phenotypic acquisition that do not involve the use/disuse of organs.
So then is epigenetic changes really Lamarck-like? I think the key here is that the *phenotype* is neither acquired nor inherited. Environmental factors produce epigenetic alterations in the parent that are inherited in the offspring BUT the phenotype that arises in the offspring from these epigenetic alterations (the alteration in gene expression) is typically NOT the same phenotype that the parent acquired – in most cases there are developmental impacts on the offspring that do not manifest in the parent, among other things. In fact the epigenetic alterations do not need to have any impact on the parent at all, and the entire phenotypic effect may be seen only seen in the offspring.
Finally, as far as we currently know, epigenetic alterations do not appear to have a significant direct impact on the evolution of diversity. The epigenetic alterations in gene expression that the offspring inherits do not endure through subsequent generations for long – I think there is some evidence that it can get as far as the third or fourth generation (grandchildren, etc), but no further unless the environmental trigger persists to reset the epigenetic alteration. “Hard-coding” the epigenetic alteration to phenotype such that it persists through time and becomes a source of evolutionary diversity still requires a mutation that fixes the phenotypic plasticity into the genome.
So, at least to me, epigenetic inheritance really *isn’t* very much like Lamarckism at all.
An example of pseudo-Lamarkism I have read about here in Colorado: The same plant can be found growing at different elevations, and will have a different physical form above timberline than in the more hospitable montane or sub-alpine environments. I.e., some of our tiny, ground-hugging tundra flowers are the same species as the wildflowers that bounce around on tall stalks in meadows, though this is not immediately obvious. But here is the pseudo-Lamarkian kicker: If you take seeds from one environment and plant them in the other, supposedly it takes two generations to fully make the shift to the other form. The ability to adapt to different environments is coded in the genes and selected for by natural selection, but there is also a mechanism by which one generation can “warn” the next about conditions. This of course would also be a genetic trait, a handy one, and therefore encouraged by natural selection…but it sure looks like Lamarkism in operation.
@9 cervantes
– You do realize, perhaps on second or reading, the troll-like nature of this sentence?
– I’m trying to remember a time when someone got into “deep water” in the “kingdom” for asking an honest question similar to “why does x not mean y,” or “how does z affect w,” etc. IE, clearly stating a divergent understanding and questioning a percieved discrepancy.
– This has all the appearance of the feigned bravery and taunting for either attention or a slap, depending on the intended goal.
– If you’re after understanding, and even if your own understanding is deep enough to counter a different understanding, you don’t need to do this crap.
– And IF it’s just a case of really wanting an answer, and trying to bump the question, just ask twice. Due to the sheer weight of troll flesh around here, putting on the makeup is likely to attract the cameras.
This sounds to me like an excellent area for a sort of Baldwin effect to drive evolution, no?
Epigenesis is, in a sense, simply another kind of developmental plasticity. It is not Lamarckian.
@ Amphiox 16
I think that “Lemarkian phenomena” as I normally see the examples would be a phenomena where physically altering one form into another results in that form being transmitted through inheritance. I think that part of the conceptual difficulty is related to comparing “physical changes” to “external changes” or “external alterations” (which can be all sorts of things that would make sense for an organism to be sensitive to.
A key point about epigenetic phenomena here is that they are all composed of parts that are all under selection and to which Darwinian principles apply. They are “above genetics” at a system level and and connection to Lemarkian patterns will involve a blend with Darwinian patterns by necessity.
If the phenotype is produced by a system that offers a range of possible responses based on environmental experience, the particular setting can be seen as an inherited phenotype (that may display differently in a particular person’s life-experience and environment). Increased anxiety-like behaviors in a hostile environment for example. Whether or not there are any epigenetic alterations that produce offspring changes but not changes in adults is an interesting issue. What research are you thinking about?
I don’t agree that epigenetic alterations would not have an impact on the evolution of diversity. But this is where the Darwinian component of the phenomena dominates. These systems are themselves under selection and I would not be surprised to see variation that alters various response settings, entry or exit from settings, intensity of signals associated with the settings…
I bloody love the Polypteridae. As a caudate enthusiast (also known as a freak), any group of fishes with external gills in the juvenile phase and lungs is something i’m going to love.
They are also significant to me because i owe them a beautiful moment when i realized that external gills and lungs were plesiomorphic for osteichthyes and not just for sarcopterygii which led to a domino effect of realizations and things making all the sense in the world, which always feels fantastic.
@8 Crip Dyke
Out of my depth, but trying to follow… (so if this is a derail, please say so).
I *think* I’m having trouble with the word “subsequent” here, and in attempting to parse into my head, I get the following and very similar rewordings for the second to last sentence. (Note that I am NOT suggesting any corrections, only trying to get what’s there.)
Unrelated mutation *restricts* a genome to an environment in which a previously available capacity phenotypic adaptation becomes advantageous.
Some occurence *isolates* the genome (or separates a portion of the genome) to an environment in which a previously existing capacity for a phenotypic adaptation becomes advantageous.
@21 Brony
Are you saying that there is a “Lamarckian component?”
…uh…
@knowknot
It’s a bit of a phantom, but can have the aspect of Lemarkian evolution. Any “Lemarkian component” will be a heritable setting (transgenerational and otherwise) of a system constructed of parts that all have Darwinian features.
Are there any examples of acquired immunity to a pathogen being passed down to the next generation after exposure? It seems to me that while DNA cannot support anything like Lamarckism, if an organism had another mechanism of passing things from one generation to the next in addition to DNA, that system could support Lamarckism. Memes, for example, could behave in a Lamarckian fashion.
@Azkyroth
That’s a good example of something relavent. A related phenomena is hyperstimulation. Searching on the term gives lots of little specific examples in various diseases and states with respect to specific neurons and such. You could describe overtraining as a kind of hyperstimulation.
Another hypothetical possibility is the association of autism among career types like engineering and in science. There might be some sort of hyperstimulation of cognitive systems that can be inherited, or become more likely through the environment. But other than referencing the correlation that is still being explored I’m not dismissing environmental chemicals or other things that are being looked at (those chemical will be acting on a system though). I’m not leaving myself out of such possibilities because I’m considering the possibility that my families military/conservative religious heritage is related to my ADHD and Tourette’s Syndrome (but that is just something I am mentally “playing with” and has even less going for it than the correlation with autism).
@26 Brony
@knowknot
Nah, your questions are good. I worked in a lab studying epigenetics in corn for five years where I picked up on some of the history. From what I remember scientists were reluctant to accept the phenomena for a while because it “looked like Lemarkianism” so it’s understandable if the wider cultural appreciation of the phenomena gets muddled in different ways.
Strictly, yes. But the fact that the system is designed to respond to environmental changes creates some usefulness in the analogical use of Lemarkian evolution (but as you can see above we are all using lots of “” and **). It’s like comparing how DNA works to a code, it can be useful but is going to be limited in ways.
It will be a functional set of parts under Darwinian selection that are involved in responding to the environment.
Brony-
Thank you. Seriously.
Working on it.
Yes — adaptive immunity in bacteria via CRISPR.
I’m not even going to try and explain it in a comment. Maybe I should write up a summary sometime.
Is Darwinian really a clear concept in this context or even a scientific term
You have change (evolution) between generations
You have variation in populations
This variation can be inherited
Natural selection will determine if individuals survive long enough to reproduce leading to a change in population
None of this requires genes, DNA or even for something to be ‘alive’.
I’m not sure why if a organism acquires an inheritable trait after its first (or only) cell is created stops any of the above being true. Can anything be ‘Darwinian’ if it talks about DNA or epigenetic which is something Darwin wasnt aware of.
Revising my final life sciences course on evolution at the moment and epigenetics = Lamarkism is described as ‘controversial’ which in exam speak mean no one is going to ask a question on it.
Anyway general point describing something as ‘Darwinian’ is not very useful
I had an exchange with cicley in the lounge where I was interested in her families experience of ADHD where some of this was tossed around if you are curious. I’m only putting in two links so I don’t trigger the moderation trap (if it’s more than two), but some of the previous conversation might be useful if you are curious.
http://freethoughtblogs.com/pharyngula/2014/08/20/lounge-473/comment-page-1/#comment-840109
http://freethoughtblogs.com/pharyngula/2014/08/20/lounge-473/comment-page-1/#comment-840160
Uh, 34 was directed at knowknot.
@mrjonno
It’s not clear too often. This is because you can use the concept of Lemarkian evolution in an analogical sense to understand epigenetics, but it’s not literally that, it’s a collection of things under Darwinian selection that function in responding to the environment.
Yes. But some of the change is because of systems that alter anatomy, physiology and behavior. It’s not precisely evolution if these (poorly understood) changes were already there in terms of phenotype possibilities.
Some individuals have setting A, some have setting B, some have setting C… it’s not the same as changes in DNA sequence.
The system can be A in the first generation. Something changes in the environment that results in a biological reaction that results in the system going to B. If the environmental change persists B will also persist.
Natural selection in terms of DNA and mutations will act on the components that make up the system. These will make the components individually and as a whole more, less or identically fit depending on if they are beneficial, detrimental, or neutral.
Natural selection in terms of the different environmental variables will act on the systems that detect the change and result in switches from A, to B, to C…
It does require genes and DNA because the components of the systems are coded in the DNA. The “alive” issue is more philosophically complex than I can manage at the moment.
In this conversation Darwinian is basically about the DNA. Epigenetics and development are a systems level above that. The critical difference is the selection on the parts of the system, and the selection for responses to environmental variables.
Just about any scientific term can change it’s meaning over time depending on what we discover. Some meanings become useless or less useful. Sometimes we need to invent new terms. It’s a necessary part of the system.
The usefulness depends on the context. But if scientists are themselves having conflicts over how to use them best than of course we will see issues here in the general public.
Good. ADHD is something I
squirrel!
PZ,
I was reading your old piece on genetic assimilation (linked in today’s entry) and was surprised by this: “One of the biases inherent in with working with many lab animals, such as Drosophila or the zebrafish, is that we suspect that development in these fast-growing model systems is highly canalized, i.e. relatively rigid and very strongly determined. Focusing on these organisms gives us an underestimate of the range of variation present in the development of less tightly constrained species.”
Why do we suspect this? What kind of evidence is there? My first guess was the opposite, that species that produce tons of offspring and don’t care for them as much would tolerate a higher failure rate during development, i.e. be less canalized.
pshaw. here in Hobbiton they bloody well climb ropes:
http://www.scoop.co.nz/stories/SC0905/S00020.htm
it should be described as “non existent” since the only cited examples of it, epigenetics, aren’t at all what Lamarck was talking about.
epigenetics is NOT Lamarckism
there are no examples of Lamarckism, anywhere.
Well, shit.
I say “shit” because despite loving science I was always a colossal failure at biology. I took Biology 101 and got a “C”. Did Biology two-oh-something and had to withdraw because I was completely crap at it. And after reading this posting and other postings by PZ, as well as some very nicely crafted explanations in the comments by some of the regulars, I find the flames of interest fired up again for biology. This stuff is fascinating, now that I can semi-get my head around it.
Thanks for the knowledge-nudging, PZ and others. Maybe this time around I won’t drop such a great big bollocks on my studies.
The idea of inheriting acquired characteristics goes back before Lamarck, as in ancient-Greece back.
Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck took that for granted while producing otherwise scientifically productive concepts. [Having his name linked to a fallacy in itself disproves any notion of cosmic justice. See link (Panda’s Thumb) for an appreciation.]
One of his contributions was the word “biology”. So, in an etymological sense, we can call fairly that entire science Lamarckian.
History has not been kind to the Chevalier de Lamarck. The hypothesis now known as “Lamarckism” was not even his. He simply wrote a popular book wherein he described that hypothesis, and it got attached to him. Then Darwin came along and took the scientific community by storm, and the idea that Lamarck put in his book (which was not his) became the de facto “look at this old silly idea that we now know is totally wrong” example to contrast with Darwin’s ideas for historical and teaching purposes.
And now the man is remembered chiefly for being wrong about an idea that was never actually his to begin with….
Also, Darwin’s own theory of heredity turned out to be…Lamarckian. The idea that heredity was not the direct transmission of phenotype, but of an abstract genetic intermediary, was so counterintuitive that no one came up with it before Mendel (at least, as far as I’ve been able to find). There was lots of foreshadowing of Darwinian evolution, but the weirdly novel revolutionary idea turned out to be Mendelism.
I think most of us are still infected by the naive view on evolution of “single cells changing into human beings”. At least I am. I should know better, but sometimes it catches me by surprise, for example when fish grow legs (exaggeration intended) because that was one of the major steps in the process of “single cells changing into human beings”. Now the fish don’t really grow legs. They exercise. That’s pretty obvious, but sometimes obviousness is not so obvious.
@36 None of this requires genes, DNA or even for something to be ‘alive’.
It does require genes and DNA because the components of the systems are coded in the DNA. The “alive” issue is more philosophically complex than I can manage at the moment
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Point I was making it required an inheritable component, it doesn’t require DNA/genes which is just what Earth life happens to use
ok, I’ll bite. what does non-Earth life use?
Kryptonite?
Presumably some sort of complex chemical molecule that could be but is unlikely to be the same as DNA