The definition of macro vs microevolution

Thanks for that correction, John,
What are the scientific definitions of micro and macro evolution?

Would you have any recommendations as to how I should respond to people who say, “I believe in micro- but not macro- evolution?”

There’s more than one definition of macroevolution, which is confusing, but the prevalent one is “evolution beyond the species level”, i.e. evolution that is not microevolution, defined as “allele frequency change within a population”. The classic macroevolutionary process is species selection, a difference in the rate of speciation or species extinction between taxonomic groups.

Creationists commonly redefine macroevolution as “evolution I refuse to think happens” and microevolution as “evolution I’m willing to accept”. Therefore the common ancestry of lions and cheetahs involves microevolution, while the common ancestry of chimps and humans involves macroevolution, which of course doesn’t happen.

First you would have to find out what they meant by that. I suspect that they mean that big changes can’t happen, with “big” defined as whatever they notice and don’t want to believe. I personally would use the argument that those big changes must have happened because of all the evidence favoring common descent of species with and without those changes. (But that could be just because I’m a phylogeneticist. Other biologists may have a different favorite argument.) Whales are a good example, with both fossil and DNA evidence showing them deeply embedded within the even-toed ungulates. Primates are another good one, with humans deeply embedded within the apes. It can’t be impossible if it actually happened. Of course the fact that it happened doesn’t tell us why it happened; as far as the phylogenetic evidence is concerned, whales could have evolved from ungulates because God wanted it to be that way and pushed them in that direction. If the push were subtle enough, there could be no evidence to distinguish divine intervention from natural processes.


Microevolution is defined as evolution within a species. Macroevolution is defined as evolution at or above species level. Macroevolution occurs when you get selection pressure acting on the entire species, say through geographic isolation which causes one species to split into two distinct reproductive groups, each of which then follows their own evolutionary pathway.


Fundamentally microE and macroE both occur through the identical mechanisms of genetic variation in each generation acted on by selection pressures. Macroevolution is just accumulated microevolution over a longer time and wider selection pressures.

Ask them what barrier prevents microE changes from accumulating over time into macroE changes. Ask them why they can walk 100 yards but can’t walk 5 miles given enough time. :slightly_smiling_face:


I would disagree with that definition. Selection isn’t a necessary feature of macroevolution just as it isn’t necessary for microevolution. And there is some argument over whether speciation is microevolution, macroevolution, or something in between.

I would disagree with that too. There are definite macroevolutionary processes that can’t be reduced to microevolution. And some of them seem important. One can, for example, consider the K/T asteroid as an agent of macroevolution, causing differential extinction based on characters for which there was no possible selective response within species.

That’s not bad. I like mine, though.

The environment immediately after the impact was the selection pressure. Some species survived, many others did not. The ones which survived continued to evolve and speciate. Your distinction makes little sense.

Yes, of course. But it wasn’t selection on a microevolutionary level, within species. There was no time for any response to selection within species when much of the extinction occurred within an hour or so and much of the rest within a year. Selection in that case happened without any allele frequency change within any population, just the elimination of populations that happened to possess the wrong characters. That’s species selection, not natural selection as it’s usually defined. And there is also species drift; some species were just unlucky; any endemics in the impact area, for example.

Now does it make sense?

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So? The sudden extinction wasn’t macroevolution without microevolution. Species which survived were the identical species they were before the impact. The surviving species continued to microevolve until eventually they reached the point of macro change. Your distinction still makes no sense.

Sigh. Species selection is considered macroevolution. Differential extinction due to characteristics of the species is species selection. The K/T event was differential extinction due to characteristics of the species. This is not me making stuff up, you know. Are you at all familiar with the literature on macroevolution?

Sigh. The species which existed immediately after the impact were the same species they were before the impact. They didn’t suddenly macroevolve into new species. The conversation is about how much physical change has to happen to a species to call the change macroevolution and what causes that physical change. Not an argument over semantics. Not saying you are wrong, just what you offer is not pertinent to the points being discussed.

Double sigh. You have a nonstandard definition of macroevolution and a nonstandard definition of speciation. I’m guessing that you are not a biologist. Is that correct? I’m also guessing that you are not familiar with the scientific literature on macroevolution and on speciation. Is that correct?


Macroevolution Definition

Macroevolution refers to the concept of large-scale evolution that occurs at the level of species and above.

Biology Dictionary: Macroevolution.

I am using standard accepted definitions of both macroevolution and biological speciation. Since you’ve appointed yourself King what are your “official” definitions? Do you really claim the K-Pg impact caused species to macroevolve all at once?

You didn’t answer my questions, so I’m going to assume that the answer is “no” for both of them. Yes, you have quoted the definition of macroevolution, but I don’t think you understand what it means. And your implied definition of speciation seems to demand that some large change, probably in morphology, must happen. Not true at all. A change in the composition of a biota is macroevolution, just as a change in allele frequencies is microevolution, even though no change occurs in any individual. A difference in speciation or extinction rate is macroevolution, even if no change occurs in individual species.

Speciation is the evolution of reproductive isolation between populations. No morphological change at all is necessary, and in fact there are a great many cryptic species that have been recognized solely on the basis of DNA sequence differences.

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Is it possible there are multiple legitimate, but different, definitions of macroevolution?

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From John’s prior post…

LOL! Yes I cited the definition germane to the conversation which agrees exactly with what I posted earlier but it’s still wrong. :rofl: :rofl: :rofl: Since you’re so busy telling us what an expert you are I’ll remind you the conversation is about Creationist claims microevolution in species is fine but macroevolution of species is impossible. Do you have anything intelligent or pertinent to add?

No I didn’t imply that at all. I was merely referring to Creationist claims small genetic changes are possible but large genetic changes are not. Try harder to follow the actual conversation.

Not anything further. Thanks for asking.

I suspect* sometimes it was. It wouldn’t have been the case that all species were either eliminated or unaffected; those species that survived would have lost some of their population, whether through starvation from insuffiecent food to support large size, inability to hibernate for long enough or simply incapability of holding their breath underwater while the fireball raged above. All these traits vary across a single species.

*Deliberate British understatement highlighted for international audience.

Of course, sometimes. But for the species that went extinct it wasn’t.

I would say absolutely yes. Heck, there’s multiple legitimate definitions of species. Moreover, the difference between microevolution and macroevolution can be an arbitrary line drawn by humans.

If we are looking for an objective definition, the best definition I can think of is essentially the divergence of species. If you start with one population that splits into two populations followed by a statistically significant divergence in the gene pool of the populations then you have macroevolution. Even then, there are problems and caveats within this definition (e.g. horizontal gene transfer, hybrids, selection of previously existing variation). Other definitions are obviously subjective, such as drawing a line between micro and macroevolution when looking at the the accumulation of change within a single lineage.

The division between micro and macroevolution is largely driven by humans creating easy to understand categories and concepts to make sense of a messy biological world. For whatever reason, we humans prefer black and white over shades of gray.

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I don’t think that covers it well. In the scientific literature, the focus is on macroevolutionary processes, those that can’t be reduced to microevolution. Species selection is the most prominent: differential speciation and extinction based on characteristics fixed in the species. It’s directly analogous to natural selection, with populations analogous to individuals, speciation analogous to reproduction, and extinction analogous to death. And microevolution is analogous to mutation, i.e. a source of variation. It can result in great changes to the biota that can’t be reduced to allele frequency change in populations. It’s not necessary that there be zero selectable variation in the populations, only that the selectable variation is insufficient to affect the outcome; either the variation is too small or the selective regime is too strong and quickly established, as in an asteroid strike that turns the sky into a broiler.

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