PZ Myers has started a thread on the definition of evolution [An exercise for the readers]. Here is PZ's choice ...
Evolution is a well-confirmed process of biological change that produces diversity and coherent functionality by a variety of natural mechanisms.And here's what I posted in the comments on his blog.
The minimal definition of evolution is ..This is always an interesting discussion and the comments on Pharyngula make some good points. What do Sandwalk readers think of my definition?Evolution is a process that results in heritable changes in a population spread over many generations. [What Is Evolution?]The truly shocking thing is how many believers in evolution get it wrong. Unfortunately, that includes you PZ. Two of the absolutely essential features of any definition of evolution are: (1) it requires permanent genetic changes and (2) it is populations, not individuals, that evolve. Both of these restrictions are missing from your definition.
What this means is that there are lots of things covered by your definition that do not fit into the scientific definition of evolution. I'll leave it to your readers to come up with a list of such changes.
52 comments :
It sucks. It's taylor-made for the hegemony of population genetics. Population genetics is a very bad framework indeed for evolution in general. It does not satisfactorily adress the origin of evolutionary novelty (you'll need evo-devo there) It loses the organism from sight, collapsed between gene and population. ..population genetics is great for answering questions about... population gentics! but it sucks at questions like how did some fish evolve limbs or a capacity to breathe air.
A definition of evolution with no mention of the phenotype is just silly (and reductionist). It all happens there. Darwin knew better.
Aboiut PZ's defintion...even crappier. Yaylor-made to fight creationist...I think it's just pathetic. Scientifically, completely useless.
for a guy that criticizes zoo-centrism, I hope you understand how the notion that populations evolve is tailor-made for sexual organisms.
The first and most fundamental evolutionary change is organic, structural change, at the level of the individual.
THEN we may get to the population level
I think your definition is pretty good...certainly better than PZ's. I would quibble with the "over many generations" wording, though. Can evolution not occur from just one generation to the next?
My own offering was: Evolution is the change in the distribution of heritable traits in a population over time.
Which is actually pretty close to yours.
I think you guys are just playing anal retentive word games. We all know what is meant by evolution. But you should least specify "Darwinian" evolution, since in it's broadest sense evolution just means "change over time".
I can play these games too. Suppose the human species starts modifying it's own genome in a heritable way? I would consider that to be evolution, but PZ's definition would fail ("natural" mechanisms), and Larry's would too ("many" generations).
What do Sandwalk readers think of my definition?
Oh, it's fine (but "descent with modification" is shorter), and I have started to refer to it a lot. But as the task was to describe evolution for a lay audience (answer "What is evolution" in one sentence), it isn't necessarily the best answer.
Reposting my own answer:
Hmm. That is like someone requesting a one sentence description of gravitation.
What would one describe, the basic phenomena ("attracting masses"), the basic definition ("gravitation is a process that results in a mass giving acceleration in a test mass"), the process ("massenergy tells spacetime how to curve, and spacetime tells massenergy how to move"), or the current theory (Einstein's field equations)?
Considering the audience I would go for the basic phenomena ("heritable changes") instead of a basic definition ("evolution is a process that results in heritable changes in a population spread over many generations", or "descent with modification" for short).
"Evolution is the change and diversification of organisms over generations" sounds good to me, cribbing from ACW's answer.
Suppose the human species starts modifying it's own genome in a heritable way? I would consider that to be evolution, but PZ's definition would fail ("natural" mechanisms), and Larry's would too ("many" generations).
What an interesting opportunity to display more anal retentivity, as I can now reformulate from another comment from the thread:
It is the duty of a theory and its descriptions of observed mechanisms to flesh out and fulfill the definition. For example, for the definition of gravitation, how much acceleration a mass will give to a test mass.
But there is confusion in that there isn't any reason to let a basic definition of a process exclude similar processes; the definition should be short, general and inclusive. It is, as I observed above, the natural task for a theory to exclude other processes.
The theory of evolution is about biological evolution, and for example genetic algorithm software will not exhibit all the mechanisms and other phenomena associated with biology. (At least not yet.)
Similarly to a basic definition of evolution, or the process of life as a population knows it, one can make a consistent definition of a living (individual) organism:
"An organism is the unit element of a continuous lineage with an individual evolutionary history."
[Sorry, Sanders, a genuine population level definition of evolution, organisms, life and 42.]
Note that this is also inclusive, so multicellulars, unicellulars, viruses, plasmids and other evolutionary elements can be included as soon as they have individual histories, as well as software if you wish.
So IMHO human manipulation wouldn't count as natural evolution which the theory describes. But part of it would certainly be related, just as domestication (and its artificial selection) is related to, indeed partly identical to, natural selection.
I believe you have pointed out a possible failure of inclusion in Larry's minimal definition, that "descent with modification" doesn't necessarily have. But OTOH "many" could be just more than one, depending on theory, and would then describe genetic modification between one generation and the next. :-)
Excuse me, while I go and freshen up. :-P
sanders says,
It does not satisfactorily adress the origin of evolutionary novelty (you'll need evo-devo there)
That's because evolution does not require mutations.
Thus, there's a very good reason why the minimal definition of doesn't address the origin of novelty (i.e., mutation).
Let's do a thought experiment. Imagine an isolated population of pine trees on some remote island. Imagine that you prevent any new mutations in that population. Over time, the pre-existing variation will be eliminated by random genetic drift or natural selection and the population of pine trees will eventually have no variation.
Is that an example of evolution?
Re: pine tree thought experiment
I vote "not evolution" with the idea that genetic change without phenotypic change doesn't count.
That's because evolution does not require mutations...Is that an example of evolution?
What? Wow...I thought evolution was a theory that explained "The Origin of Species". Your pine tree example would never ever in a bzmillion years generate anything close to a new species. It's demographic fluctuation, not evolution. Need mutations IMHO.
Anonymous;
Humans are natural - we are part of ecosystems and differ little from other organisms. Your example is perfectly captured by PZ's definition. Anyone who defines the actions of humans as unnatural is ignorant basic biology.
The definition of individual is problematic - a human consists of a population of cells. Many entities can act as both populations and as individuals depending on how they are viewed. Humans have fuzzy edges about which it is unclear as to where their boundaries are found.
Humans can even be viewed as communities laden with commensal prokaryotes and eukaryotes.
Evolution: changes in allele frequencies in a population over time
I don't think either of you have the gestalt of evolution. The best definition I've heard, and have subsequently co-opted for my own use, is "Heritable change over time."
It leaves mechanisms, scope, and scale all by the way-side and cuts to the core of what you want to say. The change could be changes in allele frequency. It could be mutation. It could be the result of incorporating a plasmid, or what have you. It could even be Mary-Jane West-Eberhard's magical heritable environment. If you're attempting to describe such a broad host of phenomenon as evolution encompasses, a broad definition is a must.
Humans are natural - we are part of ecosystems and differ little from other organisms. Your example is perfectly captured by PZ's definition. Anyone who defines the actions of humans as unnatural is ignorant basic biology.
I'd be inclined to agree with you, except that would mean that "whatever is, is natural". "Natural" would then become a rather meaningless word, since it's meaning would overlap with "artificial". The more commonly understood definition of natural excludes mankind's intentional actions.
I have a couple of difficulties with your definition:
Why do you say many generations? Doesn't evolution happen even over short periods of time?
Why do you say that evolution is a process that results in change, rather than just the change itself?
I'll have to agree with Toms. Evolution seems to be the sum of all heritable changes in a population of replicators resulting from a combination of selection processes which influence replicative success.
I think there is an important difference between evolution as a kind of process and evolution as a particular historical event.
Jeff,
Natural is contrasted with supernatural. The belief in human exceptionalism creates endless problems - it allows people to believe they were specially created, it allows people to reject animal research, it allows people believe pristine wilderness excludes humans, it allows people to believe resources aren't limiting - just to name a few.
Humans are just another species and not something special - we are bound by the same laws by which all other living things are bound.
Larry,
Your pine tree example is evolution - how could it not be? extinction like death is a part of life - not all species speciate just like not all individuals reproduce.
michaelf says,
Your pine tree example is evolution - how could it not be?
I agree. It's definitely evolution in my book even though there are no mutations.
It doesn't count as evolution by PZ Myers' definition because it's not producing diversity.
Greg Laden says,
I think there is an important difference between evolution as a kind of process and evolution as a particular historical event.
I agree. There's a big difference between evolutionary theory and the history of life on Earth. While evolution explains that history it's not true that unique events, such as the origin of birds, is part of evolutionary theory.
The role of evolutionary theory is to provide the mechanisms and processes that cause evolution.
The definition of evolution, which is what we're supposed to be discussing here, is something else entirely. The definition is supposed to help us decide what is evolution and what isn't.
Natural is contrasted with supernatural.
This is an old discussion, but to those who believe in what you call "the supernatural" - there is only what "is", and that is natural.
But that's besides the point anyway. Language is about communication, and most people will still see "natural" and "artificial" as antonyms.
NOT evolution. But first, some aclarations.
Larry's has shown us that he can apply his definiton.Evolution is change in gene frequencies . A reduction of frequencies is therefore evolution. An vice-versa, right? That he can apply howver does not make to nay more convincing. I use another definition that also has its own rules to answer that question. I like this other definition much better than Larry's, of course.
But before, some aclarations and customary finger -wagging:
Larry says above that inheritable= genetic (on which he's wrong, of course). Larry's evolution is the same ole dated definition of Dobzhanky's, thinly veiled.
It would be good that Larry researched what both his nominal "heroes" Lewontin and Gould have had to say about Dobzhasky's definition. They don't like it. Mayr doesn't, either. Well of course they don't: The phenotype is missing.
But Dawkins would probably find mentioning the phenotype innecesary, as he tends to think in terms of the ole genotype= phenotype fallacy. Indeed, not only the phenotype but also the environment are in the genotype for Dawkins.
Oh and there is that matter of what are the limits of that blob that we call the population and what sense does it really make, specially for asexual organisms. What is the biological reality of such an evolutionary unit? Surprisingly, if you look up the what Theodosius and neodarwinian synthesis have said, this is a geographic region with arbitrarily defined limits.
I'm not saying these studies are not interesting, only that they are more akin to a demographic and ecological level of description. No matter how cool these studies may be, they are limited as such, and do not prove that the population is the basic unit of evolution.
Those levels of description, in which population gentics is very useful, can clearly be trascended nowadays, theoretically and empirically.
OK so why NOT EVOLUTION? Because I use another, phenotypic defintion of evolution.
Evolution is the transgenerational repetition of a new phenotype. (descent with modification)
IF your example simply wants to visualize a scenario where no actual new phenotype or organic change has arisen in the population, then, it's not evolution. Without organic change, there's not much to be explained, isn't there.
But, if a new phenotypes would repeat itself generation after generation , because of noise or the shift in environmental conditions, according to my definition, evolution could occur. Without mutation.
Larry: heritability of traits changes with the environment, in case you don't know. There are some pretty dramatic examples.
Even with no new mutations, the environment can determine changes in gene expression un thus uncover new phenotypic effects of "hidden" genetic variation.
Larry, modernize your views. Include the phenotype, and environmental modification. Evolution without these is simply unrealistic, ideological, and above all, Passé.
Snaders says,
Larry, modernize your views. Include the phenotype, and environmental modification. Evolution without these is simply unrealistic, ideological, and above all, Passé.
It's you who's stuck in the past. Environmental modifications are not evolution. Phenotypic change is only part of what counts as evolution.
If you insist on restricting evolution to changes in phenotypes then you are eliminating most of molecular evolution since it's largely based on neutral alleles. That causes some problems because then you can't uses molecular evolution as confirmation of what you would call "real" evolution.
What would you call molecular evolution under your definition? Would it be "molecular change?"
Most changes in the DNA composition do not interact with anything and trigger no effects beyond themselves. Similarly, many shifts in the environment of an organism do not interact with an organism or alter its phenotype. Despite their structural reality and recurrence, neutral genetic and neutral environmental change do not amount to an evolutionary process. They can only become part of the evolutionary process if they become relevant to a new phenotype and its transgenerational repetition. Most of it never does.
Note that by no means am I saying that these changes must be ignored , are unworthy of description, or of no evolutionary relevance; From a systemic point of view, these can be considered as structural changes, without changes in the interactions. My only point is that, by themselves, they do not amount to an evolutionary process, and therefore do not always have evolutionary consequences or become part of an evolutionary process (even if they sometimes do).
Unstable phenotypic changes, that are not repeated across generations (developmental noise, for instance), do not amount to an evolutionary process either.
Similarly, I am not saying that changes in population gene frequencies,with no new phenotype (larry's pine example) has no evolutionary relevance or would not be worthy of description. But by itself, it does not amount to the status of evolutionary change (note that by Larry's definition, it does)
Sanders says,
Most changes in the DNA composition do not interact with anything and trigger no effects beyond themselves. Similarly, many shifts in the environment of an organism do not interact with an organism or alter its phenotype. Despite their structural reality and recurrence, neutral genetic and neutral environmental change do not amount to an evolutionary process.
That's like saying random genetic drift is not one of the mechanisms of evolution.
Your position is interesting and it's much more common than most people realize—although in most cases the proponents of such a position don't even realize the implications of what they're saying.
We need to decide on a definition of evolution. As far as I can tell, the consensus opinion in the field is that changes in any heritable character consititute evolution whether or not they are associated with a phenotype. All of the textbooks agree.
Thus, the onus is on you, Sanders, to win over the majority to your side. Good luck.
Meanwhile, it is disingenuous of you to engage in arguments about evolutionary theory when using a definition of evolution that is different from the consensus definition. You will need to make it clear that your disagreement is about how to define evolution and not about how to interpret data or mechanisms.
Sanders says,
Similarly, I am not saying that changes in population gene frequencies,with no new phenotype (larry's pine example) has no evolutionary relevance or would not be worthy of description. But by itself, it does not amount to the status of evolutionary change (note that by Larry's definition, it does)
Okay. So you reject the pine tree thought experiment on the ground that the change didn't involve any alleles that express a phenotype.
That was not part of my description so I don't know why you made the assumption.
Let's be more specific. In the pine tree thought experiment the original population has two alleles at the gene controlling needle cluster size. One allele gives five needles per cluster and the other causes clusters of three needles. (This is a real difference in pine tree species.)
There is no difference in the fitness of trees with three or five needles per cluster. (Don't quibble about this. It is a given in this thought experiment.)
Over time, the allele for three needle clusters is lost from the population by random genetic drift. Eventually, all of the trees have clusters of five needles. This is a change in phenotype. Is it evolution?
Over time, the allele for three needle clusters is lost from the population by random genetic drift. Eventually, all of the trees have clusters of five needles. This is a change in phenotype. Is it evolution?
With this new specification, I would now call this evolution.
It might not be the consensus view, but logically, I think Sander's definition is more useful than the others presented on this page. My quibble would be to add a refinement about the general unidirectionality of heritable phenotypic change (it's not really evolution if the phenotype is easily reversible).
Here's a thought experiment back at both Larry and Sanders:
Take the pine trees on the island. A protein in one of the trees spontaneously undergoes a prion-like three-dimensional configuration conversion that makes needles blue instead of green. The prion-configured protein is present in pollen such that eventually, all of the trees are converted to blue needles by the action of the needle-color-protein configuration, even though there hasn't been any alteration in the trees at the DNA or RNA level. Is this evolution?
I had assumed exactly waht you say, a decerase in diversity without any new phenotypes.
Patently, that is a change in the populatio, but no phenotypes have changed. There is no NEW phenotype.
Beieve it or not true phenotypic innovation is the very soruce of evolution. Organic change, not demographic change.
so, quite clearly still NOT evolution, in my defintion. It's easy.
Anonymous,
YES, evolution
Though I'd never heard of THAT non-dna inheritance mechanism before hehe
Over time, the allele for three needle clusters is lost from the population by random genetic drift. Eventually, all of the trees have clusters of five needles.
Isn't the generation of diversity an equally important part of the process?
Let me continue the experiment above...
One tree undergoes a heritable point mutation at the allele resulting in clusters of 7 needles. The 5-needle jobbies are lost from the population by random genetic drift and 7-needle trees take over.
Now it's closer to having all the components of evolution, I say. (Maybe it's still missing phenotypic change/selection?)
I agree that drifting of alleles is a mechanism of evolution, but not sufficient. You need include the generation of allelic diversity in the first place, no?
Sanders: I'd never heard of THAT non-dna inheritance mechanism before
Prions: Stanley B. Prusiner -- Nobel Prize in Physiology or Medicine 1997
Prions fold other proteins into prions. You may call that some kind "non-genetic inheritance" if you wish (to me we ain't eve talking about organism there) , but it does not mean you just get to postulate prions to explain the non-genetic inheritance of a trait in a multicellular organism as a pine. That has never been observed and mechanistically raise quite a few questions. I wonder if anyone has even proposed such a thing.
I kinda doubt it.
"One tree undergoes a heritable point mutation at the allele resulting in clusters of 7 needles"
You are certainly not missing phenotypic change. That's it.
Bayman, the whole point of the pine tree thought experiment was to demonstrate that you can have evolution without mutation.
A population can evolve without generating diversity. There shouldn't be anything in the definition of evolution that rules out the loss of diversity in a population as an example of evolution.
Larry,
without phenotypic change?
Naaaa. Reduction of diversity of the phenotypes in a poulation may or MAY NOT have any evolutionary consequence.
The point is that in itself it is not evolution already.
It's too broad to any population change, and so narrow you don't even consider phenotypic change.
It has loose ends: define population, define inheritance.
The population is NO true evolutionary unit
I'm sticking with organic change
"Meanwhile, it is disingenuous of you to engage in arguments about evolutionary theory when using a definition of evolution that is different from the consensus definition. You will need to make it clear that your disagreement is about how to define evolution and not about how to interpret data or mechanisms"
Actually, I want to make it clear that I disagree on BOTH.
But on the first, I would be backed up by Lewontin; he accusses Dobzhansky's definition precisely of confusing what is an explanation of mechanism with the actual phenomenon; changes in the genetic composition of populations are supposed to explain the observed evolution, not BE evolution itself
The fact that your definition blends into mechanism is patent; it seems you can only conceive two possible evolutionary mechanisms: drift, and selection.
It also seems all your scenarios are carried out by rigidly genetically determined organisms.
These misconceptions are unfortunately quite common. Understanding evolution requires way more than understanding drift and selection. Open Gould's Book, Larry, and read the chapters about how development "constrains" evolution. Maybe you can find a dose of respect for evo-devo more similar to that shown by the late maestro.
Sanders says,
The fact that your definition blends into mechanism is patent; it seems you can only conceive two possible evolutionary mechanisms: drift, and selection.
Hmmm ... either you didn't read my essay [What Is Evolution?] or you didn't understand it.
I defined a minimal version of evolution. A definition that could be used to determine what is, and what isn't, evolution at the level of population and individuals.
As I made clear in my essay, there's more to evolution than the minimal definition. For example, I said ....
I agree with Gould. That's why I think it's important to explain the real biological definition of evolution as a change in the heritable characteristics of a population over time. We can explain that this is a minimal definition, and that there's more to evolution than this, but we shouldn't back away from the real meaning of the term since it conveys some important messages. If we cave into pressure from the general public to make evolution into something they can understand, with all their biases, then we will have lost the battle before we even begin.
The amazing thing about the minimal definition of biological evolution is that it doesn't carry any baggage concerning the history of life or its future. As soon as we try to define evolution in terms of the historical record, we run into all kinds of problems because we confuse evolution as a process with evolution as a history of life. The scientific definition attempts to describe the minimum thing that might be called evolution. We know that the history of life is more complicated than this and we know that evolutionary theory encompasses other things such as the formation and extinction of populations. There is no conflict between the minimal definition of evolution as a change in the genetic composition of populations and macroevolution. Gould understands this.
The point is you FAIL to describe the MOST minimal requiremente for evolution: phenotypic change.
I fail to see how what you say about separating the history has anything to do with our debate.
Othe than that, the reaosn why we have some people that are dogmatic and want to know nothing for instance, about how epigentic plasticity relates o adaptation..they don't have to!! with your definition, all they need to grasp is drift and selection. That's it! Yepeee!
This is why defendign a definition that is tailor-made to the reductionsits neodarwinians who invented it has a corrosive effect.
I once again recommend you see what Gould and Lewontin think about that lousy defintion of evolution.
The amazing thing about the minimal definition of biological evolution is that it doesn't carry any baggage concerning the history of life
Baggage? Explaining the history of life is why biology needed the concept of evolution in the first place. This is the point.
The scientific definition attempts to describe the minimum thing that might be called evolution.
Well if this is the aim, I have an even simpler definition - one word - unrolling. Or simply change if you prefer.
I biology, I think we use the term in a much more specific sense. It describes a theory that accounts for the origins of species, embryos, cells and genomes. As such, it is an alternative to creation.
In biology, evolution is not just change, it's a very specific type of change that's capable of producing very specific results.
Without phenotypic change and natural selection, evolution as a theory is no better able to explain life than creationism. But arguably it could do without random drift and a lot of other types of change that seem be encompassed by your definition.
Bayman says,
Well if this is the aim, I have an even simpler definition - one word - unrolling. Or simply change if you prefer.
That's a nonsensical definition, but I think you know that.
Perhaps you could offer a realistic definition that captures what you're trying to say? Maybe you could lift it from one of the major textbooks on evolution to show me that it's a definition that has wide support among evolutionary biologists?
A lot of people seem to have idiosyncratic definitions that have no hope of achieving consensus status. What's the point of that? You can't talk intelligently to your colleagues if you don't even agree on how to define evolution (or the history of life).
You can't arbitrarily rule out random genetic drift as an evolutionary mechanism just because you, personally, don't like (or understand?) it.
It's part of evolution as defined by most evolutionary biologists. If it is ruled out of bounds then molecular evolution will no longer be about evolution but about something else. How silly is that?
Those of you who claim that (visible?) phenotypic change is the only kind of change allowed in evolution are horribly out of date. That notion went by the boards over 50 years ago.
Those of you who think that natural selection is the only allowable mechanism are even more old-fashioned. You're still living in the nineteenth century.
"Those of you who claim that (visible?) phenotypic change is the only kind of change allowed in evolution are horribly out of date. That notion went by the boards over 50 years ago"
That's like saying that accepting continental drift is outdated only becuase it's a long-established truth. What was weird was that neodarwinians managed to fool themselves into ignoring the phenotype (and the genotype-phenotype relationship, that is, Development).
I think that your definition is just a neodarwinian platitude. Without reference to the phenotype it is quite worthless.
"Those of you who think that natural selection is the only allowable mechanism are even more old-fashioned. You're still living in the nineteenth century"
But you are just one step away from that. All you do is "Add drift". It's still all about genes taking over the population, no?
I want to explain a bit more about whether neutral genetic change is evolution or not.
My answer is: it is change in the genotype, not the phenotype.
In first place, you must accept that even at the unicellular level, there is a divide and non-equivalence, between genotype and phenotype. The genotype represents a subgroup of molecular cellular components (the DNA).
Of course, structurally you can say that the genotype is part of a cell-phenotype, and call that evolution. I think that on tahta argument I would have no problem in calling that molecular evolution or genotypic evolution, but we must keep the genotype-phenotype distinction crystal-clear.
I liked derekjames's definition the best so far. I have a few thoughts:
Evolution is a phenomenon that we seek to explain. As such, incorporating any mechanism into the definition conflates model and data and should be avoided.
Often, point mutations in proteins are neutral in their immediate effect, i.e. they produce no discernible phenotype. However, by changing the context of future mutations they can have a profound effect on outcomes. Consequently, even mutations that do not appear to change the properties of proteins cannot be viewed as insignificant. Similarly, because non-transcribed DNA serves as a source of new proteins, new domains, and altered regulatory structures, changes in it cannot be disregarded. The upshot of all this is that the genotype/phenotype dichotomy is not particularly informative or useful in terms of defining evolution (it is of course still helpful in explaining evolution).
Evolution is a property of populations, not individuals. The question is what is the relevant population to consider.
"Evolution is a property of populations, not individuals"
Wrong. Evolution is a property of individuals AND populations. In fact, a property of individuals first;THEN a property of populations.
I continue to be amazed at how the current paradigm leads so easily to forget the importance of the transformation at the individual, organismic level, be it by mutation or environmental modification.
Phenotypes are traits of individuals; to make evolution observable at the organismal level has a structural and biological reality that is quite more patent than the arbitrarily chosen geographic limits of the darwinian population (That is the darwinian mindset: it's all about populations. Not my vibe, precisely)
"However, by changing the context of future mutations they can have a profound effect on outcomes"
Agreed, but not by necessity will it have that profound effect, either. The other mutations DO have to occurr, to begin with (My own impression is that lots of genetic variation comes and goes without ever having had an effect).
Until that precise context emerges, it is just part of the usual background of neutral molecular variation. I think it may be OK to call this neutral change molecular evolution, but keeping very clear that it is indeed "purely molecular" evolution, with no accompanying phenotypic change.
Why is nobody talking up that PLOS paper on palau man?
My opinion: "H, sapiens", my ass!!
You can't arbitrarily rule out random genetic drift as an evolutionary mechanism just because you, personally, don't like (or understand?) it.
No. This is my point, that in biology the definition of evolution is not something you or I or a consensus of textbook writers make up, it's a description of a process that accounts for a natural phenomenon: life.
Darwin and his contemporaries weren't playing semantic games when they introduced evolution into biological thinking, they were explaining the natural world.
So I think the bounds of our definition ought to be specified by what is necessary to explain the distinguishing characteristics of life and natural history.
I think Darwin's theories hit evolution right on the head, and I don't see that anything new has emerged from the last 150 years of biology that justifies modification.
So, I like the "old-fashioned" definition of evolution as consisting of two essential aspects:
1) (Common) Descent with modification.
2) Natural selection.
It's pretty similar to your Neodarwinian definition except it doesn't limit evolution to genetic change, but simply heritable change (not all genetic change is of evolutionary significance, and not all evolutionarily significant change is genetic). And second, it explicitly recognizes natural selection as the shaping force behind progressive evolutionary change. This is essential because it explains the obvious directionality that distinguishes biological evolution. Evolution is not just a random walk through phenotypic space.
Oops. Noticed looking back your original definition indeed said heritable not genetic. I like it.
Larry said:
< "That's because evolution does not require mutations.
Thus, there's a very good reason why the minimal definition of doesn't address the origin of novelty (i.e., mutation).
Let's do a thought experiment.
Imagine an isolated population of pine trees on some remote island. Imagine that you prevent any new mutations in that population. Over time, the pre-existing variation will be eliminated by random genetic drift or natural selection and the population of pine trees will eventually have no variation.
Is that an example of evolution?" >
This doesn't make sense. To say that evolution doesn't require genetic mutation is like saying "change doesn't reqire changes". If anything can be said to evolve,there is mutation involved.
Genetic drift results in mutations in a population anyway.
What is called "natural selection" amounts to the same thing as,say,elephants with tusks being blown away by hunters at a higher rate than those without tusks,resulting in a lessened frequency of elephants with tusks being born - except that where humans are involved there actually is selection involved. Is that an example of evolution?
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