Definition of evolution and the distinction between micro/macro


(Christy Hemphill) #1

I’m pretty sure that changes in allele frequency in a population over time is the definition of evolution everywhere and it is exactly what biologists mean by evolution. The only people who talk about “microevolution” are people who reject common descent. “Microevolution” is the exact same process as “macroevolution,” just with a smaller window of time in focus.


Genesis 30&31, selection and applied Evolution
(Chris) #2

I mentioned Endor; my mistake, it should have been Endler; but at the time didn’t have access to the reference, so here it is now;

You can also look up the term on Wikipedia to find “Microevolution is the change in allele frequencies that occurs over time within a population.” and “… it was not until Russian Entomologist Yuri Filipchenko used the terms “macroevolution” and “microevolution” in 1927 in his German language work, Variabilität und Variation, that it attained its modern usage. The term was later brought into the English-speaking world by Theodosius Dobzhansky in his book Genetics and the Origin of Species (1937).”
Both Filipchenko and Dobzhansky are evolutionists so you can blame them for the use the terms. Creationists had nothing to do with it.

Not in my experience. I have done two certificate level MOOCs run by universities and both used the terms micro- and macroevolution. The terms are used on the Berkley Evolution 101 site. The chief problem with the terms is that they are loosely defined and as a result many Creationists prefer to not use the terms either.

And no, I don’t accept that ““Microevolution” is the exact same process as “macroevolution,” just with a smaller window of time in focus.”

All this is getting quite off topic so I won’t discuss it any further in this thread but am willing to do so in a different more appropriate thread.


(Christy Hemphill) #3

I moved this side discussion to a new thread because I think it encapsulates a common misconception that would be useful to others to clear up. Notwithstanding your 42 year-old source and Wikipedia article, I don’t think you are right about microevolution being distinct from macroevolution or about the definition “change in allele frequency in a population over time” not being the standard definition of evolution across disciplines. But I am not a biologist so I will leave it to others to point you the direction of more relevant and recent authorities on how the terminology is currently used.


#4

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.

In my reading, scientists use the terms in the way we would expect. Microevolution refers to a single mutation or small changes within a species. Macroevolution is the accumulation of many individual mutations and is used to describe the differences between species, be it between two living species or between a living species and a fossil species. There are also large scale genomic changes that can occur, such as whole genome duplications or recombination events that radically change the structure of the genome, but I’m not sure how they fit into this terminology.

The point of contention within the YEC v. Evolution debate seems to be over the idea that small changes can accumulate into large changes over time. I have yet to see anyone from the YEC/OEC/ID camp explain why small changes could not accumulate to the point that they result in the differences we see between species at the level of the genome, and that seems to be where the debate is stuck. I have yet to see anyone put forward a mechanism that would stop the accumulation of microevolutionary events. It seems inevitable that mutations will accumulate over time, so I’m not sure how those who argue against microevolution accumulation into macroevolution have a leg to stand on.


#5

Why not? Let’s use the chimp and human genomes as our example since both genomes have been heavily studied and are easily compared through online databases. Can you point to a single difference between the human and chimp genome that could not have been produced by microevolution?


(Christy Hemphill) #6

You are right. What I should have said is that the only people I hear using the term microevolution as if it is somehow a fundamentally different process than macroevolution are people who reject common descent. Over and over again you will hear anti-evolution proponents say that they accept microevolution but not macroevolution. Or that there is plenty of evidence of microevolution but none for macroevolution. Making a distinction between the two based on something other than the time scale in view is a common rhetorical tactic in anti-evolution literature.


#7

There are different mechanisms for each, but not in the way that creationists think there is. Microevolution is changes within a population while macroevolution is divergence between populuations. Therefore, macroevolution would be microevolution with the additional mechanism of genetic barriers that prevent free gene flow between populations. WIth a lack of gene flow you get different mutations accumulating in each population, and this causes the two populations to become less and less similar over time.

In essence, macroevolution is speciation.


(Ryan weatherly) #8

Ring species such as ensatina salamanders help illistrate speciation in progress .


#9

Allow me to submit to the discussion Douglas H. Erwin’s paper, “Macroevolution is more than repeated rounds of microevolution” (2000, Evolution & Development 2(2):78-84 - free PDF available here). He points, among other things, to the whole-genome duplication hypothesized to have taken place in an ancient vertebrate lineage, which I would say fits the bill as an example of a macroevolutionary change distinct from microevolution.


#10

As far as I am aware, there haven’t been any whole genome duplications since the common ancestor of primates, yet most YEC/OEC/ID proponents would consider the evolution of primates from a common ancestor to be an example of macroevolution. If genetic recombination is considered to be macroevolution, then the recombination event that resulted in the cit+ E. coli strain in Lenski’s long term evolution experiment would be an example of macroevolution which I doubt most YEC proponents would accept. I would also hazard a guess that there are many heterozygous alleles in the human population that were produced by genetic recombination which most would not consider to be macroevolution.

I would fully agree that differences between species is more than just substitution mutations, but I don’t see how the problem is solved simply by labelling large indels or recombination mutations as macroevolution.


#11

I don’t really care what “YEC/OEC/ID proponents” are saying. Douglas Erwin is neither. I’m responding to the claim that the only people who differentiate between the mechanisms of microevolution and macroevolution are people who reject common descent. That claim is incorrect.


#12

What is interesting is that what Ewert defines as macroevolution is defined as microevolution by other scientists:

“The extensive whole‐genome duplication within basal vertebrates evidently provided them with a different path to morphological complexity ( 1; Valentine personal communication). Whether such changes constitute macroevolution has been the subject of dispute. For example, 50 has argued that such changes are microevolutionary, while 24 proposed an explicitly hierarchical model of evolution of Hox elements. 11 essentially split the difference, arguing that the recruitment of genes for new functions has progressively altered patterns of morphological change, from gradual to more discontinuous.”–Ewert (2001) [note: the numbers in the quote match up with references found at the end of the paper]

Even in Ewert’s example the line between micro and macro appears to be subjective and arbitrary.


(Tom Larkin) #13

This was an issue a while ago and many Christians state that they do not object to evolution within a species (termed “microevolution”), only to evolution above the species level (termed “macroevolution”). In fact, there was a scientific Macroevolution Conference in the early 1980’s (see Science Letters 20Feb1981) in which the conclusion was that the process for macroevolution was not well understood at this time and the mechanisms for macroevolution may be different from microevolution.

Christians who dispute the theory of evolution often also cite the lack of evidence for transitional species.

Since the early 80’s there has been a great deal of discovery in both the area of genetics as well as the discovery of fossils. Revised theories have been published demonstrating that macroevolution and microevolution utilize the same mechanisms, just over a much longer time frame and on a grander scale (references: Mayr, Earnst. (1988). Toward a New Philosophy of Biology: Observations of an Evolutionist. Harvard University Press. ISBN 0-674-89666-1 and Kutschera U, Niklas KJ. (June 2004).”The modern theory of biological evolution: an expanded synthesis”. Die Naturwissenschaften.91(6):255-76.)


(Stephen Matheson) #14

This perfectly illustrates why @Christy’s point is correct and important. In lay conversations, it is clear that critics of evolution think that there is something mechanistically or even conceptually different about “macroevolution.” It’s easy to see why: it is common for people to picture macroevolution as “big change from one thing into another,” which is what it is, except then these people picture it happening in one or a few steps. Hence the ludicrous questions/comments about cats turning into dogs etc. Here, Erwin is 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. Much of what he writes is straight out of the evo-devo playbook, which I personally like a lot, and some of his suggestions and ideas are nearly obsolete (as should be expected from a nearly 20-year-old paper written before the genomic era). What Erwin is NOT saying is that macroevolution is separable from microevolution. Here’s a quote:

But discontinuities have been documented at a variety of scales, from the punctuated nature of much speciation, to patterns of community overturn, the sorting of species within clades by differential speciation and extinction, and finally mass extinctions. These discontinuities impart a hierarchical structure to evolution, a structure which impedes, obstructs, and even neutralizes the effects of microevolution. As is so often the case in evolution, the interesting question is not, is macroevolution distinct from microevolution, but the relative frequency and impact of processes at the various levels of this hierarchy.

So it is true that evolutionary biologists are intensely interested in topics like innovation and evolvability. (Our journal has published some great examples.) To understand, for example, differential success of distinct clades, one needs an explanation that operates at a level above “changes in allele frequencies over time.” That is much, much different from asserting that “macroevolution is distinct from microevolution.” To me, that’s gibberish.


(Stephen Matheson) #15

A great point. It’s interesting that @Krauze focused on WGD but not on the major themes of Erwin’s essay, which are the kind of macroevolution that biologist talk about: evolvability, clade success, morphological innovation, even phenotypic plasticity and evolutionary capacitance, which are two mechanisms known to “buffer” evolutionary change so that rapid morphological change can emerge from boring old genetic diversity. The difference between point mutations and CNVs is interesting, but not worth inventing new prefixes for. The difference between clades with regard to diversification and innovation… now THAT’s some macroevolution worth discussing, but it’s just not the same as the “macroevolution” of the under-informed religious apologist.


(Ryan weatherly) #16

Speciation :
speciation. (spē′shē-ā′shən, -sē-) n. The evolutionary formation of new biological species, usually by the division of a single species into two or more genetically distinct ones.

In layman’s terms , offshoot species can no longer interbreed with the parent species and produce viable offspring …

This is evident and varified in countless species …
Macroevolution


(Chris) #17

Definition of Evolution

We should start by distinguishing between the dictionary definitions of evolution and when the word is used as shorthand for The [Neo] Darwinian Theory of Evolution. The basic dictionary definition is “change over time” without even specifying whether that change is towards an improvement or greater complexity.

Within the context of this forum I will be attempting a definition for The [Neo] Darwinian Theory of Evolution.

I don’t think we can with justice condense such a definition into a few words, any more than we could define Einstein’s Theory of Relativity in a single sentence without losing much of what it’s about.

Going back to Darwin the title of his book was On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life). Although Darwin used the term evolution several times he didn’t define it and it apparently had a broad general meaning rather than referring specifically to his theory. E.g. “At the present day almost all naturalists admit evolution under some form.” (p168). (Darwin was also not using the term Species in our modern sense.)

What are the key ideas that Darwin proposed in his book? I think the central idea is contained in the conclusion “There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.” And as argued in the book he believes that Natural Selection is the means by which this happens.

The modern synthesis marries Darwin’s ideas with genetics and particularly with mutations as the means of providing new variations for natural selection to work on. Most proponents today propose that all life is descended from a single common ancestor. Some additional ideas are Neutral Theory and Punctuated Equilibrium but these are not central.

So here’s a short definition


(Chris) #18

For comparison look at definitions by Kerkut and Coyne

"On the other hand there is the theory that all the living forms in the world have arisen from a single source which itself came from an inorganic form. This theory can be called the ‘General Theory of Evolution’ ", Kerkut, G.A. (1927–2004), Implications of Evolution.

“Life on earth evolved gradually beginning with one primitive species—perhaps a self-replicating molecule—that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.” Jerry Coyne, 2009, Why Evolution is True.

Later I will come back to discuss micro vs macro but I have other things to do right now.


(Chris) #20

Except that this definition is commonly not used. Recently biologists declared that the African Savannah and Forest elephants are two different species; despite there being existing hybrid populations. There are many cases of cross species and cross genera hybrids within our current classification system. Many of these hybrids can produce viable offspring.

So it appears that a species is whatever a competent taxonomist decides that it is. This is a large part of the difference between “lumpers” and “splitters”.


(Ryan weatherly) #21

Breeds , sub species , species …
I admit , it does get blurry sometimes , but I was under the impression we were discussing macroevolution .
Polar bear and grizzly were not able to produce viable offspring at first , then began to produce fertile offspring …
Chimps and humans can no longer breed , yet at one time , we did …
It would seem persistence pays off .

Darwin stated that if the domestic breeds of pigeon had been encountered in the wild , they likely would be considered several species .
( If you don’t know , nearly every domestic pigeon stems from the rock pigeon )