Definition of evolution and the distinction between micro/macro


(Jeff Schloss) #82

That is quite right: allopatric speciation requires character divergence based on allelic changes. However, chromosomal rearrangements are textbook mechanisms (whether efficacious or not) or parapatric or sympatric speciation.


(Haywood Clark) #83

So are you retracting your claim?


(Jeff Schloss) #84

Not in the slightest. I never mentioned allopatric speciation, which you seem to have conflated w/ sympatric speciation.


(Christy Hemphill) #85

So, if I continue to say that the definition of evolution is “change in allele frequencies in a population over time” or “descent with modification” are we in agreement that it is sufficiently accurate for most lay level discussions? I get it that experts in the field find it not wholly adequate, but I’m personally not going to be referring to “changes in ploidy associated with heritable phenotypic changes” or any form of speciation, be it allopatric, parapatric, or sympatric. (Sorry, @JeffSchloss )

If you told me an adjective is a word that describes a noun, I could point out a number of ways that definition is inadequate and inaccurate for linguists, but for most people’s purposes it works just fine. So, going back to the OP, am I okay saying “change in allele frequencies in a population over time” is the (a?) standard definition of evolution across disciplines, or not?


(Stephen Matheson) #86

It is a standard definition. @JeffSchloss is right to note that we can see changes in allele freq without other change, and vice versa, but I don’t think that the complexity of evolutionary biology means we can’t use summaries and “definitions” like yours. My preference has always been “descent with modification” but that emphasizes the “common descent” branch of evolutionary biology while omitting mechanisms of change (selection, drift, tinkering by unnamed superintelligent meddlers, the usual). Your definition is about the genetic end of things but neglects common ancestry and glosses over the very interesting reasons why genetic change and phenotypic change can be seemingly uncoupled.

Is the “allele frequencies” summary “inadequate”? Well sure, but I don’t suppose anyone thinks it could possibly enfold all of evolutionary biology. But it’s also accurate, and important to reemphasize regularly in places like this one, where “evolution” is widely misunderstood and laughably misrepresented.


(Jeff Schloss) #87

Yep, both are fine and some version of both is found in most texts. Re the first, you’d be a bit better off with “genetic change over time,” since it encompasses more than changes in allele frequency. Thanks for convening convo.


(Chris) #88

Now I’ll move on to micro vs macro.

As I have said previously these are general terms and not precisely defined, so there will be cases that could be assigned either way depending on your view.

Here’s a good collection of definitions at ThoughtCo.

Several would include speciation in macroevolution but others don’t. For instance Douglas J. Futuyma:

macroevolution A vague term, usually meaning the evolution of substantial phenotypic changes, usually great enough to place the changed lineage and its descendants in a distinct genus or higher taxon.

Kirk Durston in Microevolution vs Macroevolution: Two Mistakes suggests definitions that “distinguish between microevolution and macroevolution in a rigorous scientific way”.

Microevolution: genetic variation that requires no statistically significant increase in functional information.

Macroevolution: genetic change that requires a statistically significant increase in functional information.

In the article he provides links to define “statistically significant” increase in “functional information” and how to measure them, so read the article before you comment on these.

Anyway, gtg and watch netball with my wife.


(Jon Garvey) #89

Precisely the point I made to @T_aquaticus. The same would probably go for the need to distinguish macro- from micro-evolution as theoretical constructs.


(Chris) #90

No. The real problem is confusion at best or equivocation at worst.
E.g. Evolution (a change in allele frequencies in a population over time) has been observed so we know evolution (common descent) is true.
In fact the biggest danger is that you can fool yourself when you use the same word for two very different concepts.


(Jon Garvey) #91

But isn’t the whole point of a definition to provide the exact boundaries of how something (in this case, the world “evolution” is represented? How can one misunderstand or misrepresent something whose definition is already acknowledged as “inadequate to enfold all evolutionary biology”?

The question of whether something is a truth from the bit of evolutionary outside the definition, or merely laughable, becomes somewhat arbitrary, as was pointed out over a century ago:

“When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean — neither more nor less.’

’The question is,’ said Alice, ‘whether you can make words mean so many different things.’

’The question is,’ said Humpty Dumpty, ‘which is to be master — that’s all.”


(Jon Garvey) #92

Just a rider to that - just two years ago a professional (but anonymous) biologist here put me, very tersely, in the “misunderstanding” category for describing, rather than defining, evolution as “change in gene frequency.” No true scientist, he said, would fail to speak of “change in allele frequency.” The citations I found in the literature for my usage he dismissed out of hand.

Now I find my own past usage being suggested as a good enough definition of evolution. How do we know whether to anathematise the ignorant who use “gene” instead of “allele” for what, in fact, is more definition of population genetics than of evolution? By majority vote at BioLogos? We have to say on either definition that Darwin did not study evolution at all, and neither did the orthogenic majority before the Modern synthesis. And we have defined away any future (or past) discoveries of non-genetic inheritence as being outside the purview of evolution.

All of which are why I go along with those who prefer “common descent with modification” as a definition of evolution, and the more restricted definitions for the more restricted disciplines that study its mechanisms - and whose individual influence will inevitably change over time.


(Chris) #93

There was a farmer.

He had a flock of white sheep and one day he bought a black ram to service them. Over the course of a few years the number of black sheep in the flock increased. (the ram was doing his job.) In other words there was a change in allele frequency in the population over time, which is as discussed above, microevolution.

How long will it take for this to produce a new species of sheep? Forever! This is not the sort of change that will produce a new species, even if the entire flock becomes black sheep.

How long to produce an animal that is no longer a sheep? Even longer than forever. Clearly in this case microevolution continued for a long time will not result in macroevolution.

So when someone tells you that macroevolution is just microevolution over a longer time scale, remember this flock of sheep, and realise they are just trying to pull the wool over your eyes.


(Ashwin S) #94

92 posts on the “Definition of evolution”…
Wow…


(Mervin Bitikofer) #95

This would be reasonable in an earth only a few thousands of years old. But of course on that perspective, hundreds of millions of years becomes the “forever” that your narrative forbids.

Can everybody agree on this? As a non-specialist, merely thinking of common descent through gradual modifications is enough to capture the broad scope of evolution, is it not? You highlight the importance of having precise boundaries for it, Jon, but is such precision really necessary? We could point out many problems in a similar way about heliocentrism and get bogged down in whether or not astronomers today should consider themselves “heliocentrists”, since it is not a true view of the universe. But isn’t it enough to know that an earth moving around the sun is closer to a true picture of reality than vice versa? In the same way aren’t most here (even among specialists) going to be happy if common descent (by whatever combinations of mechanisms) is recognized as closer to physically descriptive truth than separate, recent, de-novo creations?


(Ashwin S) #96

Hi Mervin-
gradual could be a problem… The term gradual would need a definition…


(Christy Hemphill) #97

I believe he was suspended for exactly this kind of annoying tendency to condescendingly nitpick everyone. It’s not like said user had BioLogos’ blessing to be a jerk.


(Mervin Bitikofer) #98

Why?

In fact I probably could have left the word out entirely if it really bothered anyone. “Common descent” alone probably captures things most broadly. How it all happened, or how fast can be happily argued over by all interested parties.


(Christy Hemphill) #99

A thread on the definition of “day” in Genesis would probably win a post count competition any day though.
234
346


(Mervin Bitikofer) #100

On any 24 hour day?


(Ashwin S) #101

Probably… but then it’s surprising that an idea that is “scientific fact” has controversies in how it’s best defined…
Wouldn’t you say so?