Macroevolution is microevolution over a long period of time.
OK, I guess you wanted a bit more than that. First of all, let’s see what some others say is macroevolution.
Macroevolution can be defined simply as evolution above the species level, and its subject matter includes the origins and fates of major novelties such as tetrapod limbs and insect wings, the waxing and waning of multi-species lineages over long time-scales, and the impact of continental drift and other physical processes on the evolutionary process.
In any case, macroevolution involves long time periods and large changes to lineages that result is what we would call new kingdoms, phylums classes, orders, families, or genus.
The critical point in both these definition is time. The simple reason is that we cannot see, in our lifetime a population evolving beyond the species level. In fact, even if we did see this happen, we wouldn’t notice it. Why?
Because it is the nature of humans to put things into discrete boxes. Even when they don’t fit into discrete boxes. I’ve brought this up before and I’ll bring it up again. The cline, or ring species. Very simply a species spread out over a large area may be able to interbreed with it’s neighbors, but not with their neighbors.
A – B – C- D – E – F
A and B can breed together, but A can’t breed with D, E, or F. So are A and F the same species*? Some would say yes, because there is a complete series of interbreeding populations. Some would say no because A and F cannot breed together. But they can’t draw a line anywhere in that sequence to say species one on the left and species two on the right.
This is, to put it mildly, a huge problem. The blood tends to get deep in conferences that talk about species.
Now, if we have A – - – - – F, then there’s no problem. They can’t interbreed, so therefore, they are different species. Easy. But we still have these clines, ring species, and intermediates.
Indeed, even if we only have A and F now, at some point in time, there were intermediate species. If humans happen to be around and keeping records when there are intermediates, then A through F are the same species. If we don’t see the intermediates, then A and F are different species.
So, our entire classification system and the difference between microevolution and macroevolution are based entirely on whether humans have seen the intermediate species or not.
That’s why I’m not a fan of even the words ‘microevolution’ and ‘macroevolution’. They are not two different things. Macroevolution is just an extension of microevolution over a long time. It’s just evolution.
But what happens over long periods of time? Well, that’s when things get more interesting. That’s when we start to see major differences in once closely related species. Once those major differences appear, then we could easily define the group as a new genus and bang, there’s macroevolution.
Wait… what? That’s all it takes for macroevolution?
Technically yes. Species, indeed the entire scientific nomenclature and classification system are human constructs. They really have no bearing on the reality of life on the Earth. Keep in mind, we’re using a system that has been updated, but the basics are almost 250 years old.
Macroevolution is another term that’s completely man-made. Even the concept is man-made and has no bearing on the real world. You see, in spite of what creationists believe, no organisms popped out fully formed. No dinosaur gave birth to a robin. No lizard gave birth to a mammal. No fish gave birth to an amphibian.
The reason that things look so distinct is because we never saw all the intermediates. For species that we know about, we can see the intermediates.
Take a look at dogs. If you compare a dachshund with a great Dane and ignore all that you already know about dogs, then you would probably come to the conclusion that they are different, but related species. They can’t mate together. The are very different in morphology. They just aren’t that similar. But, as creationists complain, they are still a dog. But what’s a dog?
Why is a wolf not a dog? I know that wolves and dogs can interbreed and wolves look more like a German Sheppard than a dachshund does. Why is a coyote not a dog? I know that coyotes and dogs can interbreed and they look a lot like some of the smaller herding dogs than a spaniel. What about foxes? What about maned wolves? See, it’s not all that easy. Answer ‘what is a dog’, just using morphological, interbreeding, and/or genetic information, then we can talk about “it’s still a dog”.
I’ll save the rest for another post on the types of speciation and why they are important and obvious to this discussion.
But I want to leave with an example of what I’m talking about. How the environment results in changes to a species and how those changes result in new species or even larger changes.
Saiphos equalis is the Australian yellow-bellied skink. The population of these skinks live from the lowlands all the way up into the mountains and the population in the mountain is changing, in a highly unusual way. (peer-reviewed article / popular article (no-paywall))
There are reptiles that lay eggs and there are reptiles that retain the eggs and give live birth. There are only three species that do both. S. equalis is one of them and it’s taken a novel approach to making sure that the embryo has enough calcium.
Embryos take calcium from the shell. This provides them with a source of the mineral and thins the shell so it’s easier to hatch. S. equalis populations in the lowlands lay their eggs with about a week or so to go. Populations in the mountains retain the eggs throughout and give live birth. The skink’s uterus secretes calcium that can be taken up by the offspring.
It’s almost the beginning of a placenta. It certainly demonstrates that the transition from egg-laying to live births isn’t nearly as complex as previously thought.
* I’d just like to point out that even the definition of ‘species’ is very, very problematic. There are organisms that are of the same species that cannot reproduce (ring species) and there are organisms of two different species that can reproduce and have viable offspring.
The question becomes where to draw the line and that is one of the most arbitrary things that we deal with in science. When talking about evolution it invariable leads to problems, because some species aren’t species and some non-species are species. Etc. etc. etc.
It is a disgustingly complex subject and no one who hasn’t really studied (I mean, studied, not just read about in National Geographic) the entire field can really appreciate how made up the whole thing is.