Reproductive isolation in artificial panspermia model

Question

Simulation of artificial panspermia, in inter-galactic travel, as a model for the study of reproductive isolation.

Case 1:

If we send a mass of proto cells(kept alive by some mechanism like cryogenic freezing powered by some perpetual engine) to another far galaxy's habitable planet, such that the cells are subject constant variations in its surroundings( the cryogenic system is made up of a material that transmits 99.9% of the incoming radiation like the the radiation of stars, and the cells are subject to gravitational wave radiations, relativistic speeds and so on), and set up early-earth-like conditions in a constructed area in the the new planet where the cells can grow into another human, (just like they did during the early evolution on Earth); would there exist a reproductive isolation between a human on Earth and the new Homo sapiens( say their new name to be- Homo galaxiants) if they tried to sexually reproduce?

Assumption: Our species survive during the travel of the cells. We, on Earth remain unevolved from the time the cells leave the Earth till the time a Homo galaxiant matures.The pollution levels, the climatic conditions, the species richness, rate of consumption, radiation of the Sun, etc., all remain the same on Earth so that the DNA can be subject to the same conditions both for an organism on Earth and for the travelling mass of cells( although this is subject to additional changes en route).

Answer 1

There can only be so much change before the DNA becomes non-viable

2500 years of mutating space radiation would be bad for cells. If humans were living and reproducing for 2500 years, then that would be a 100 generations. In each generation, some mutations would be viable and be passed on, and others would not be viable and die off. If the radiation level were high, then genetic drift could conceivably happen quickly.

However, if you are sending the people as a pile of cells, then all those mutations will happen at the same time to the sperm/egg cells of a new human. Each new human would have 100x as many changes to their DNA. Will all those changes be viable? Seems unlikely. Even if you get 99 good changes for better sight, hearing, stamina, whatever, it only takes one cystic fibrosis or spina bifida to ruin the new person.

Therefore, if you sent cells across the galaxy, either they would need to be shielded from radiation, or the resulting humans would probably not be viable.

In conclusion, the only way to make your humans valid in a far off galaxy is to ensure they are only one generation of changes away from the humans who sent them on earth. Thus the only changes will be the genetic drift of 2500 years for those who remained on Earth. And that just isn't that much.

Answer 2

Evolution is not repeatable. If they make it to the destination alive the cells will evolve, but the chance of their evolution resulting in animals resembling us is vanishingly small.

But in fact, without going into details, a strong argument can be made that the reduction of 100 initial possibilities to ten or so was the analogue of a bingo game, a grand-scale lottery. In fact any ten of the 100 could have made it. If you could rewind the tape of life, erasing what actually happened and let it run again, you'd get a different set of ten each time. There are 17 trillion different combinations of 10 that you can take from a group of 100. (Stephen Jay Gould, famous paleontologist, in an interview for the American Academy of Achievement)

Answer 3

Yes they would be reproductively isolated.

Why do I think so? Well, bats and birds can't interbreed, and neither can dolphins and sharks, and each pair have evolved in worlds with exactly the same early-earth conditions, to fulfill roles which are exceedingly similar to their other half (two animals evolved for flying, two evolved for swimming, of similar size and shape and similar sorts of "successes" I guess would be my term, and yet totally different). Even better, they share the same historical conditions with exacting precision, and a fair chunk of familial resemblance from their very-base level processes from their shared ancestors, which is above and beyond what your question requires :)

And so, if bipedal hairless monkeys evolve again from this simulation, to fit the niche of thinking predators who adapt the environment to them rather than the reverse and then tinker with the world... they would probably have less in common with human-people than a bird and a bat have in common. Evolving flight (and evolving into all the niches) is probably not more of an overlapping niche, or indeed more of a specialization, than what human-people have done.

Evolution on earth was driven by a lot, a lot of factors - including geography, local conditions, and each other. Some of which are factors we don't know. some of which are factors we can't recreate or influence, and some of which are factors tightly correlated with adapting to changing circumstances (again, including each other). we can't even run a stimulation of earth's historical conditions without running into patches where we're not exactly sure what was going on or which factors led to which results, and you would as a preliminary starter need to be able to perfectly reproduce them.

If you sent an exact replica of (early) earth, accurately programmed to change for every variable earth underwent - including cosmic radiation, precise light and gravity fluctuations, minutiae of geography including volcanic eruptions and tetonic movement, extinction events (and who/what survived and didn't), meteors and such, the moon - you still could not guarantee humans, because you can't monitor interactions of the evolving creatures with each other enough to insure evolution stayed "on course", and if you could any intervention would be "taken advantage of" or, hm, adapted around, to change the actual results.

The godling of the simulation favors primates, so now you have a thousand and a half extra primate species that survived thanks to its intervention - oops. Or else it knows dinosaurs are supposed to evolve and then go extinct, except it was juust a leeetle bit too good, and the predecessors to alligators, or some other lizards, or birds, now didn't survive, either - oops. Ah, wait, it knows that horses are gonna be really important, better make sure they don't get lost - and horses can now afford to be a little slower, a touch more arrogant, taking advantage of this invisible protection instead of getting better, and we end up with non-domesticable unicorns or thirteen extra species of zebra, instead of the horses we could breed for work and travel.

And in all those altered initial conditions and interactive shenanigans, the precursors to humans never get off the ground, or become something slightly different, and whatever ends up taking the human-people's niche (if, indeed, anything ever does) need not be any more closely related to us than a dolphin is to a shark just because they both swim and eat fish and can't stay still underwater too long or without drowning.