What’s that picture doing up there? Be patient, you’ll see. There being no news to report, we shall use this time to consider the eventual human exploration and occupation of the Milky Way galaxy. In What Are We Learning from SETI? we optimistically estimated that this might occur in as little as one million years. We’ll copy a bit from that earlier post to give you the general idea:
Assume we could travel at, say, around one-third of lightspeed, so that a large shipload of settlers could travel to a nearby star in about a dozen years. … Then assume that stars with habitable planets are, on average, not more than about 5 light years away from each other, so we can gradually expand our domain without encountering any impossible distance barriers. And then assume that each new settlement — if educated and well-equipped — could develop itself sufficiently so that in, say, about three generations (less than a century) it would be able to launch some of its own people to settle the next habitable system.
If those assumptions are reasonable — and we’ll all be dead before anyone really knows — then the domain of human-occupied space can expand every century at a rate of roughly 5 light years in every direction. That’s a sphere which grows 10 light years in diameter every 100 years. In a thousand years the sphere of human-occupied space will be 100 light years across. …
Multiply our expansion time by 1,000, and conservatively assume no technological improvements over all that time. You get a sphere of human space that’s 100,000 light years across in only a million years. Think about that. The Milky Way galaxy is roughly 100,000 light years across.
Others have made such estimates — often in the range of ten million years — but if we don’t encounter any roadblocks, then however long it takes us it’s going to happen. That’s fine, but what does it mean in terms of evolution?
Here’s where we need that picture of a peeled orange. Imagine that the Earth is at the stem, from which our brave settlers move out in various directions to occupy the habitable planets of nearby stars. Each segment of the orange represents the path taken by different settlers, heading for different stars. In due course, each path will be extended as the original settlers send their descendants ever farther from Earth, and the pattern will continue as their descendants move farther still to expand the domain of human-occupied space.
But each segment will be a separate breeding population, with the occupants of each world rarely traveling to the worlds of adjacent stars, and never going much father than that. After a few extensions of the path in any one direction, the farthest world’s people will never visit the Earth, nor will they visit worlds in other lines of expansion. The distances will be too great. Any mutations that occur will be isolated to a limited population, and will be passed on to other worlds only as each unique path is extended further into the galaxy.
Using the peeled orange as a visual aid, we can refer to each path of expansion as Segment A, Segment B, Segment C, etc. In time, say ten thousand years, because of the founder effect, the people of the most recently-settled part of each segment will have mutated into a unique sub-species — which we’ll call Sapiens 2. In another ten thousand years, their descendants who reach the farthest worlds in that segment will have become Sapiens 3, and so on.
What mutations will there be? That’s impossible to predict, but assuming they’re beneficial, we can imagine that by the time each segment has become Sapiens 3, they’ll have better mental abilities than we do (photographic memories, for example), immunity to our diseases, and perhaps much greater longevity. That’s good stuff, and it’s ridiculous for us to recommend that they take precautions against mutating “too far” away from their parent stock. After all, where would we be if our distant ancestors had followed such advice?
Mutations can also cause incidental changes that are harmless, but that go along for the ride. We see this in dogs selected for hunting, burrowing, etc. Various breeds have floppy ears, curled tails, different muzzles, coloring, etc. It’s therefore predictable that Sapiens 3 in Segment A won’t look like their distant ancestors who pioneered that segment. And they’ll be quite different from Sapiens 3 in Segment B, etc. Each segment will be mutating in its own unique way.
But so what? Even if, by the time each segment gets to Sapiens 3 or Sapiens 4, they’re separate species that could no linger interbreed, what difference does it make? It’s not as if a lonely boy on some world beyond the constellation Taurus is ever going to meet a girl at the opposite end of the human sphere, who lives on a world beyond Scorpio. So who cares if by that time they’re different species?
Human speciation may not matter for most of our expansion throughout the galaxy, but remember — the orange is round and so is the Earth. The original humans who migrated out of Africa, whose descendants followed different routes to Europe and to Asia, didn’t need to worry very much either. But eventually their distant descendants met — in the Western Hemisphere and on various islands of the Pacific. It often wasn’t pleasant, even though they were all still the same species.
What will happen when the descendants of each segment eventually get to the far side of the galaxy (analogous to the other “pole” of the orange)? Sapiens 5 from Segment A will be exploring new worlds, and they’ll encounter Sapiens 5 from Segment B who are doing the same thing. Try to imagine the movie, “Bigfoot meets the Abominable Snowman,” where each has advanced technology. Sooner or later, the same will happen with the descendants of all the other segments.
It won’t be as simple as when Hernán Cortés encountered Montezuma. That was a walk in the park — the Spanish and the Aztecs were the same species. By the time we get to the Far Side, it’s going to be a lot more interesting.
See also: Humanity’s Next Adventure — Trek Three.
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