Definition of evolution and the distinction between micro/macro


(Jon Garvey) #22

Christy, that’s not actually true, in that the term “microevolution” dates way back to the twenties, and I’ve seen it used in quite a number of papers with no anti-evolutionary influences. I’ve even seen it in a university population genetics primer, in which “macroevolution” is said to be the business of palaeontologists rather than pop. geneticists (which was, it seemed to me, rather an abdication of responsibility).

It is, however, a useful distinction for discussing whether population genetics answers all the questions at the larger scale, which has certainly been questioned on many grounds, and at many times - hence its original coining. From Stamford Dictionary of Philosophy article:

Implicit in this definition [change in gene frequencies] is the idea that evolutionary phenomena such as speciation, adaptive radiation, diversification, as well as phenotypic evolution, can ultimately be reduced to gene frequency change. But do we really know this to be true? Many biologists, particularly ‘whole organism’ biologists, are not convinced, and thus reject both the population-genetic definition of evolution and the primacy traditionally accorded to population genetics within evolutionary biology (Pigliucci 2008)…

…Authors such as Gould (2002) and Eldredge (1989), for example, have argued persuasively that macro-evolutionary phenomena are governed by autonomous dynamics, irreducible to a microevolutionary basis. Philosophical discussions of this issue include Sterelny (1996), Grantham (1995) and Okasha (2006).

I don’t think any of those sources are creationists.

As to the “change of gene frequency” definition, when I cited it a year or two ago Josh Swamidass insisted that the preferred scientific definition of evolution was “common descent”. Disbelieving him I checked around various sites, and found he was right in many cases - check this from NCSE (and this from Ted Davis).


#23

To me, this seems like one of those discussions where if someone with leanings towards teleology says that it’s a nice day out, it becomes paramount to show that it is in fact a horrible day out.

To recap: The claim was made that the only people who distinguish between microevolution and macroevolution are those who reject common descent. In response, I cited Erwin making the (I thought) pretty non-controversial point that a whole-genome duplication (WGD) in vertebrates was an example of a macroevolutionary change distinct from microevolution.

So far, no one has really responded to this point. @T_aquaticus talks about the evolution of primates and @sfmatheson talks about cats turning into dogs, even though the WGD took place in the early evolution of chordata, long before either primates, cats, or dogs had evolved.

@sfmatheson describes Erwin as “pointing to the kinds of evolutionary change that are not fully explained by microevolution, but require additional patterns to be considered and added to the explanation”, which I think is a different way of saying what I just said. He also mentions that much of what Erwin writes is “straight out of the evo-devo playbook”, which I would think underscored the non-controversional-ness of what I was saying (last time I checked, evo-devo is still an accepted field in evolutionary biology).

I have a feeling that @T_aquaticus and @sfmatheson think that we’re having a discussion about whether macroevolution is true, so to avoid any confusion I will state that the evidence for the WGD is contingent on the common ancestry of all of chordata and offers no solace to those insisting on the “special creation” of man and apes. And that there’s no reason to think that the whole-genome duplication took place through anything other than natural processes.

But the point still stands: The process that lead to the WGD in vertebrate genomes (indeed, a double duplication) is different than the “change in allele frequencies over time” definition of microevolution. If anyone disagrees, I’d love to hear their reason why.


(Jon Garvey) #24

Additional note on “change of gene/allele frequency.”

I suspect it’s less used now because it orginated from Fisher as an anti-mutationist definition at the start of pop. gen. Existing genes were generally sufficient to account for evolution, with occasional mutations “topping up the gene pool”. Within a decade or so it was found that evolution was largely mutation-driven, which is why the definition sounds slightly awkward, if useable, in these days when mutations are king.

But the definition excludes not only future possibilities in refining evolutionary theory, but current realities: cytoplasmic inheritance has been known for decades, epigenetic changes affect evolution without changing gene frequencies, and many differences between organisms are now known to be due to changes in gene expression.

That’s why I suspect there is a drift towards a more generic “common descent” definition - it allows for these mechanisms, and sits more easily with the more exotic mechanisms of change, without excluding those which may have not been discovered, or sidelined over the decades.


(Phil) #25

While there are historical examples of microevolution being used as a term, does anyone currently use it other than as used in the YEC-EC discussion, as defined by present day YEC proponents?


(Lynn Munter) #26

To be fair, the biological definition does not require improvement or greater complexity in order for it to be evolution, either.

Just to keep playing with definitions a little more, I wonder why you need the capital letters here. Does Mutation mean something other than “changes?” Is it helpful to specify “genetic Mutations” or would we be better off sticking with the original “heritable changes?” Does Natural Selection mean more than “filtered by the environment?”

Also, to my knowledge nobody is seriously claiming that all life in the universe has a common ancestor, so perhaps we can simplify the definition a bit:

All life on Earth is descended from a common ancestor and current diversity is due to heritable changes filtered through environmental gauntlets.

Thoughts?

ETA:

The definition is actually more like “populations that don’t normally interbreed in the wild,” which is subject to a lot of interpretation, as you noted. But any kind of close examination of taxonomy leads to the inescapable conclusion that the categories are more or less arbitrary human bins we chuck things into. The tree shape of common descent is real; but the difference between what is a species, what is a genus, and what is a family or order? Those are always going to be vague and permeable lines.


(Paul Nelson) #27

Go here and enter the search term “microevolution”:

https://www.ncbi.nlm.nih.gov/pubmed

In a recent book, Field Museum Curator of Evolutionary Biology Olivier Rieppel explains the origin of the words “microevolution” and “macroevolution”:

“It was Russian zoologist and geneticist Jurij Philiptschenko [Yuri Filipchenko] (1882-1930) who – in a small book published in 1927 – introduced the terms ‘microevolution’ and ‘macroevolution’ to characterize these two levels of evolutionary change…What at the time was branded as neo-Darwinian doctrine (or dogma) was the claim that all evolutionary processes, including macroevolution (i.e., the origin of new body plans), can be explained as the summation of such microevolutionary processes. Philiptschenko himself rejected that claim. The characters that mark out major body plans that characterize higher systematic categories, such as classes or phyla (i.e., echinoderms, mollusks, or turtles), differ from the characters that demarcate species and their populations in several ways, he claimed…”

See O. Rieppel, Turtles as Hopeful Monsters: Origins and Evolution (Indiana University Press, 2017), pp. 102-3; emphasis added


#28

The only place where I would disagree with Erwin is his idea that discontinuous change must involve something other than microevolution. That doesn’t make sense to me. If there is a mutation that affects a large portion of the genome or a mutation that has a large effect on phenotype, the organism with that mutation still has to reproduce with another member of that species. To me, that is still microevolution because it stays within the species. Erwin is also light on genetic mechanisms, which he admits in his paper.


(Jon Garvey) #29

Pubmed:
874 results for “microevolutoion”
708 results for “macroevolution.”


#30

A lot has been discovered since 1927, such as DNA. There were lots of crazy ideas as to how the mechanisms of change in evolution worked prior to the discovery of DNA and molecular heredity. Like many ideas in science, the scientific view of micro and macroevolution has changed as we learn more about how evolution works.


#31

There wouldn’t be hybrids if speciation was not occurring. They would simply be the same population throughout. The only way you get populations that are that different from each other is if there is restricted gene flow between the populations. That restriction in gene flow is speciation, even if that restriction is not absolute. What scientists are focused on is the effect of mechanisms, and the effect they see is two populations that are genetically diverging from one another.

Speciation can be detected by genetic divergence, so it isn’t completely subjective. Also, because evolution is a real thing there isn’t going to be a hard line between species. We should see hybrids and DNA crossing over during the early stages of speciation because that is how evolution works. It would be extremely rare for one generation to be able to interbreed and the very next generation to not be able to interbreed.


#32

In the 4th post of this thread, I wrote:

“To be fair, a search for micro- and macroevolution at Google Scholar turns up plenty of legitimate peer reviewed papers that use those terms. Scientists who accept evolution also use these terms.”

I addressed it before you did.

I disagree. WGD would be be a variation within the population, an allele. The duplication would spread through the population through microevolution.


(Phil) #33

But the question remains, does anyone outside of the narrow confines of the discussion use it? I suppose the answer is: rarely, and less frequently in the less decade, from what I can see in the articles looked at.


(Stephen Matheson) #34

Point taken! FWIW, dialogue with you is fun and interesting despite your irrational leanings toward teleology. :grin: Oh and, it’s hot and humid here in Cambridge, so don’t EVEN tell me it’s a nice day out.

Not to be deliberately burnishing my status as a grumpy curmudgeon focused on the weather, but that initial claim was criticized by @T_aquaticus and immediately reworded by @Christy. In fact, neither I nor @T_aquaticus was addressing that claim, and @Christy isn’t either. I was clear about what I was discussing.

Not with you; I know you have already affirmed common descent.

Well, now this is really just semantics and that’s not interesting at all. But “the process that led to WGD” is an unmysterious ubiquitous genetic process that is simply not conceptually distinct from anything associated with allele frequencies, selection, drift, mutation, or any other process that evolutionary biologists study. I don’t think it is possible to make a coherent argument for putting WGD in a different category from aneuploidy and then from transversion and then from CNVs and then from medium-sized indels and then from point mutations. I hope you follow that continuum and see why it’s important, because this is what both @T_aquaticus and I have asked about: why is it that some kinds of genetic changes are “macroevolution” and others are “microevolution”? Biologists simply don’t care about either that question or any answer that it would elicit.

I will excuse myself by noting that the Erwin paper is dated but interesting and is most definitely not about classifying genetic events as “macro” versus “micro.” It is about explanatory levels in evolution, and that’s an interesting topic that actually deserves the title “macroevolution.” WGD is not.


(Paul Nelson) #35

A frequently-cited urban legend among defenders of evolution is the claim that creationists devised the words (concepts) “micro-” and “macroevolution,” and that only creationists still use the terms. This is false, as the citation of Filipchenko’s work shows, and a PubMed search readily reveals.

I recommend Rieppel’s 2017 book for another reason, however. He argues that the origin of turtles provides a valuable case study in the unsolved problem of macroevolution. As Rieppel writes,

“There is no question that Darwinian evolution through variation and natural selection at the level of interbreeding populations does occur, but the question remains whether this is the only possible way of evolutionary transformation. This was one of the major questions asked, and answered in the negative, by early representatives of evolutionary developmental biology such as Stephen Jay Gould and Pere Alberch.” (Turtles as Hopeful Monsters, p. 161)

Rieppel’s book is beautifully written and illustrated – definitely worth a look.


(Stephen Matheson) #36

Also PubMed:
113,638 results for “phylogenetic”
26,354 results for “adaptation evolution” [not phrase, just the two words]

Now you have perspective on how common it is for biologists to talk about “microevolution” and “macroevolution.” Illuminating, don’t you think?


#37

I would agree, it is unfair to say that only creationists use those terms. I said as much in the 4th post in this thread.

Without any details it is difficult to address Gould’s or Alberch’s position.


(Stephen Matheson) #38

Interesting. I’ve never heard that urban legend. Is it commonly written, perhaps in books? A quickie Google search was unproductive.


(Paul Nelson) #39

S. Matheson wrote:

“I’ve never heard that urban legend.”

See the OP, above:


(Stephen Matheson) #40

Yep. It’s completely different from what you wrote about “devising the words.” I’m pretty sure that is the real urban legend. Am I wrong to conclude that your claim is false?


#41

There is a decent Nature article on micro and macroevolution:

Macroevolution: Examples from the Primate World

It appears that the main “disagreement” is between anagenesis and cladogenesis, otherwise known as phyletic gradualism and puctuated equilibria, respectively.

A couple of quotes:

“One group holds that microevolutionary processes alone can sufficiently explain grand patterns and radical changes on the tree of life. In other words, mutation, migration, genetic drift, and natural selection can produce major evolutionary changes given enough time. The key element is vast amounts of time – on a scale that is difficult for most people to imagine. This model of macroevolution is called phyletic gradualism. It proposes that most speciation events are the result of a gradual and uniform transformation of one species into a new one through a process called anagenesis.”

“On the other hand, many scientists propose that grand patterns in the history of life cannot be explained exclusively by changes in allele frequencies over time, even rapid ones. Instead, these scientists propose that large changes on the tree of life were preceded by events that decoupled the tempo and mode of evolutionary change from predictable microevolutionary processes. . . This model of macroevolution is called punctuated equilibrium (Eldredge & Gould 1972). It proposes that grand patterns of evolutionary change on the tree of life involve the rapid splitting of one ancestral species into two or more descendant species through cladogenesis, often followed by long periods of stasis in the descendant species (Eldredge et al. 2005).”

At least in my eyes, this is a distinction without a difference. In both scenarios the differences between species is due to mutations that accumulated in the ancestral population, which is microevolution.