None of these things is just like the others
In my previous post, I explored convergent evolution: when two different species, usually separated by distance, evolve a similar physical characteristic independently of each other. At the end of the post, I said that I would follow up with a post on the far more common divergent evolution.
Simply put, divergent evolution is when two groups of the same species evolve differently. The environments in which the groups live are the most common cause of divergent evolution – in other words, if two groups of the same species are separated into different environments, they will each evolve and adapt separately to fit the environment they’re in. Arguably the most famous example of divergent evolution is Darwin’s finches, which he described in On the Origin of Species:
“The inhabitants of the Cape de Verde Islands are related to those of Africa, like those of the Galapagos to America. I believe this grand fact can receive no sort of explanation on the ordinary view of independent creation; whereas on the view here maintained, it is obvious that the Galapagos Islands would be likely to receive colonists, whether by occasional means of transport or by formerly continuous land, from America; and the Cape de Verde Islands from Africa; and that such colonists would be liable to modification;—the principle of inheritance still betraying their original birthplace.”
- On the Origin of Species, Chapter XII: Geographical Distribution. Charles Darwin, 1859
The “inhabitants” Darwin refers to in the above passage are the variations of finches. (It’s interesting to note that, since Darwin was developing the very concept of evolution, he didn’t have a word for it to utilize – instead referring to it as “modification”.)
Divergent evolution can occur on both a morphological and a physiological scale. People believed that various shrimp located on either side of Panama were the same species – until the Panama Canal was opened. The groups of shrimp fought when they encountered each other, and refused to interbreed. It was discovered that although they looked the same, the groups of shrimp on either side had distinct genetic differences. It was theorized that the groups used to be part of the same group until roughly 3 million years ago, when the Isthmus of Panama rose from the ocean and separated them; they then evolved into separate species. (This is known as allopatric speciation.)
Evolution in animals is used widely in science fiction. There are countless future and near-future stories with animals very similar to, but slightly advanced from, an animal we use in present day. There are even many stories with animals that have evolved sentience and human-level intelligence (be it through natural selection or biological uplift). However, divergent evolution isn’t something we see written about much – not in animals, anyway. After all, why dwell on the differences of two groups of an animal when those same differences can be employed with regard to ourselves?
Thus, divergent evolution in humans is an extremely common trope in science fiction. There are three distinct ways this can be handled:
On-Earth: Groups of humans on Earth evolve into distinct species, each significantly different from Homo Sapien. It’s happening all around us – no reason it can’t happen to us!
Off-Earth: Humans colonize another planet or moon; they evolve in various ways to adapt to the new living environment, until there are at least two different types of humans surviving on the new world in unique ways.
On/Off-Earth: Some humans leave Earth while others remain. Humans on Earth continue to evolve, while those who left evolve to adapt to their new environment in space or on another planet. Eventually both are distinct from Homo Sapiens and from each other.
So I’m going to end this post with a fun “test”. Extrapolating from present-day, come up with one (new) idea for each of the above three types of human divergent evolution, and post them in the comments below. No re-stating something that’s already been posted either! Let’s see how many people can come up with.
Remember, this is a circumstance where we’re limited only by our imagination! The cause is usually environmental – what would a major environmental change like global warming cause? U.S. President Barack Obama stated recently that “I expect to be around to see” manned expeditions to Mars in his lifetime – how would that change us here on Earth, or the daring ones who go? There is endless potential in the ideas of what we might become!
You mean as examples in existing stories or a new scenarii?
New ones!
An interesting point is that humans can no longer speciate on earth: there are no isolated population pockets that would serve as founders for such an event. We are a single global species now, by dint of being able to travel at will (well, mostly, as the recent Icelandic eruption proved) and mating across cultural boundaries. So although local genetic and phenotypic differences do exist, we’re a monoculture — which is a bad thing, ecologically and biologically.
On the other hand, if we ever undertake long crewed space voyages and settle on other planets, we will de facto speciate — and do so much faster than we would on earth, because the pressure of radically different environments will dictate it. Of course, we may also accelerate the process by genetic engineering.
This outcome is one of the most interesting and unsettling repercussions of space travel: essentially, we will create aliens even if we don’t meet any!
I wrote about this extensively in a 6-part series titled Making Aliens, starting here: http://www.starshipreckless.com/blog/?p=24. The speciation angle is discussed extensively in the last two parts.
Making Aliens 5: Playing God II
http://www.starshipreckless.com/blog/?p=34
Making Aliens 6: The Descendants
http://www.starshipreckless.com/blog/?p=37
Athena, just because we’re a monoculture now doesn’t mean we always will be, even solely on earth. As writers we have the flexibility to imagine futures in which this isn’t so. That’s what extrapolation is for.
I thought I was agreeing with you? — and riffing on some of the points you raised from the biological/genetic standpoint.
Well, you pointed out how right now we’re a monoculture on earth, but didn’t leave open the possibility of breaking that pattern on-earth. You seemed to shut that down and imply that we’ll only break as a monoculture if some of us leave earth. My reply was specifically about the possibility of breaking from the monoculture solely on-earth. Which as writers we’re plenty capable of exploring the concept of.
We’re also capable of exploring the concept of human speciation as scientists — and since this blog is about science in fiction, we can delineate the existing constraints, which will give us a way to frame extrapolations that are not fantasy.
Along the lines of Zarpaulus’ reply in this thread, extremely lengthy and strict endogamy just might produce newish human strains. But it would take millions of years unless it’s aided by some external circumstance. You may have noticed the words “genetic engineering” in my reply, which is a path to speciation regardless of planetary context. Another path, of course (also heavily trodden in SF) is post-apocalypse mutations.
At no point did I object to your delineating the existing constraints, or say they weren’t accurate. Your comments (“humans can no longer speciate on earth”, “We are a single global species now”, “we’re a monoculture”), followed by no extrapolation but a switch to discussion of On/Off-Earth possibilities, really came across as a shut-down of a potential discussion of future On-Earth divergence. My comment was solely to re-open that discussion.
Though I think it’s a fair point. In fact, as I was reading the post itself & was thinking how speciation on Earth would require some sort of catastrophic or at least artificial event to cut one part of the global monoculture off from the other. And immediately thought of several examples from SF/F. The riffs I think of involving Earth-based speciation are variations on those themes — most involving big population reductions (due to war, disease, asteroid impact, alien invasion) that could leave different populations isolated from one another.
That’s what I was thinking too. I’ve read plenty of stories with catostrophic disasters that caused us to, well, not be a global community any more. Usually they go hand in hand with dramatic reduction of worldwide populations, too, and often there’s a loss of technology which cripples widespread communication. In circumstances like those it’s very possible we’d have pockets of people becoming isolated from the rest of the world.
I think if I ever wanted to explore one, I’d go with the asteroid “deep impact” variation. One as devastating as the one that ended the Cretaceous. Resulting mass extinction, with a long & slow recovery & lots of new species, including variations on humanity niches, with some of them holding onto remnants of the kind of civilization/technology we’re familiar with, but others evolving in different ways.
Off-Earth speciation has been done to death. Just read Larry Niven’s Known Space.
But I do have an idea for On-Earth speciation that could be unique: In the near future genetic testing for a variety of “disabilities” becomes common. However many people with disabilities, in particular high-functioning autism spectrum disorders, want their children to be like them. So they refuse genetic testing and marry within their “subculture”. Over time they become a new species, some might even speed up the process by adding extra chromosomes to their offspring’s genomes so they are incompatible with ordinary humans. This attracts a lot of controversy, especially when certain ethnic groups adopt the same tactics to preserve their genes.
White supremacist separatist cult with lots of moolah creates isolationist mega-compound & genetically engineers to ensure “purity” of its already socially constructed “racial uniqueness.”
There’s also the possibility of “time travel” allowing multiple human sub-species to be contemporaries on Earth.
A favorite way of doing this in SF seems to be to use the DNA of Neanderthals or other prehistoric human to revive them in the present day. I think there are a number of problems with this idea scientifically – not the least being that we don’t have well-preserved genomes for multiple individuals. But maybe carefully stored DNA and tissue samples from the present could be used to revive “modern” humans far in the future.
Alternatively, you could have a group of present-day humans tour the galaxy on ship traveling near light speed and time dilation would potentially return them to Earth millions of years in the future. Send out ships at regular intervals traveling different distances, and 50 million years from now there could be humans who represent samples of the species from a number of different eras.
Of course these would be individuals from a single line of evolution living together, rather than divergent evolution, but it would get multiple human subspecies onto Earth at the same time.