#this is just kind of a seat-of-my-pants infodump type post and i'm not sure if everything in it makes sense as written

[queenlucythevaliant]

Guys. Guys. My sisters and brothers in Christ. There is no meaningful way to divide “micro” evolutions vs “macro” evolution. (Explanation got long and really emphatic, so see below the cut). 

Some Christians like to use these words to distinguish current, directly observable processes of descent with modification from the cumulative sum of these processes ie “I can accept that dogs diversify into different breeds but not that all life shares a common ancestor.” This is. Really arbitrary.

Where are you drawing the line between “micro” and “macro”? Typically, people say that they don’t believe that one “kind” can evolve into another “kind.” So speciation? Because speciation is not only observable, but predictable and repeatable.

Okay, so there are a bunch of different species concepts, but for the sake of simplicity let’s use reproductive isolation because that’s what most people are familiar with. A new species emerges when a new population no longer interbreeds with an original population.

This can happen behaviorally (like if a new species of bird has a different mating dance and thus can’t court members of the original species), mechanically (genitals no longer compatible – right- and left-handed shellfish are a good example of this), or at cellular level (sperm and egg no longer compatible), or genetically (different numbers of chromosomes).

Guys. This happens all the darn time. We can watch it happen in real time and see the differences between species accumulate. We can even take a sample population, divide it in half, and subject the two subpopulations to different conditions causing them to diverge. It’s predictable and repeatable. I had a professor who did work like this in Alaskan fish capable of living in both fresh and salt water. His team was able to repeatedly create divergent fresh and saltwater exclusive populations which did not interbreed and had significant physiological differences. I had another prof who worked with cicadas and saw new species emerge because one year there was a big change in local climate and some of the five-year periodicals (I think) didn’t come out and breed for an extra year. They were reproductively isolated from the five-year periodicals that did emerge on time. Over the course of like fifty years they got more and more different from the original population and expanded to fill an empty niche and absolutely boomed in population, expanded geographical range, etc. There are journals full of this stuff.  

Okay, so maybe you mean “kinds” more generally. Maybe you consider all fishes one “kind.” In that case, how do you account for the placement of whales? Or any crown group tetrapods, for that matter? Do you consider primates all one kind? In that case, what do you make of the changes in chromosome number between types of old- and new-world monkeys? If that’s within-”kind” variation in primates, is it also within “kind” variation when it divides chimpanzees from humans? This kind of taxonomy is just entirely untenable. 

It gets even murkier when you look at microbes (my specialty), which don’t differentiate the same way that multicellular life does. Microbes reproduce asexually, and their main source of variation is horizontal gene transfer. As a result, there’s a lot of gray area between microbial species and even very different species are capable of swapping DNA under certain, not-that-unusual circumstances. So even if you want to say that all fishes, for example, are one “kind," then you basically have to group every prokaryotic species together the same way because they are way more reproductively compatible with one another than any broad group of animals you could think of.

And remember, microbes account for the overwhelming majority of life on earth—there are at least 100 million times more bacteria in the oceans than there are stars in the universe. Is this “micro” or “macro”? Mechanistically, it’s much less dramatic than so called “macroevolution” in animals, yet the scale, breadth, and timeframe involved would likely be considered “macro.” Not to mention, getting from the origin of life to the origins of multicellularity encompasses many more large evolutionary leaps that getting from multicellularity to modern man. If you’re willing to call microbial evolution “microevolution,” then you’re seventy-five percent of the way to just accepting that humans share a common ancestors with all other life on earth. If you’re not, well, there goes the entire “kinds” schema again. 

Okay, so maybe the difference between “macro” and “micro” evolution isn’t speciation or “kinds”. Maybe you think that “macro” evolution refers to the greater processes by which very divergent species (say, humans and redwood trees) evolved from a single common ancestor long ago in deep time. Maybe the distinction between “macro” and “micro” evolution is essentially an historical one.

Apart from being very subjective, the big issue with this distinction is that it means that processes which observably occur in the present must have occurred either differently or not at all in the past. This is an absolutely wild claim, and I can’t think of any other subject about which people would say this.  

This would be like saying—huh okay, now I gotta come up with an analogy—it would be like saying yes, I accept that fashion trends change season-to-season at present, but I’m not willing to accept claims that neckties could have come from cravats given enough time. It just defies logic.

Finally, it bears saying that “micro” and “macro” evolution are not scientific terms. I cannot state this emphatically enough. I have never once heard these terms from any professor, bio student, or serious publication. The only place I have ever seen them is in YE Creationist discourse. Christians made them up because some would like to hold two essentially incompatible positions.