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## How Many People Does It Take To Colonize Another Star System?392

Hugh Pickens DOT Com writes: "The nearest star systems — such as our nearest neighbor, Proxima Centauri, which is 4.2 light-years from home — are so far away, reaching them would require a generational starship. Entire generations of people would be born, live, and die before the ship reached its destination. This brings up the question of how many people you need to send on a hypothetical interstellar mission to sustain sufficient genetic diversity. Anthropologist Cameron Smith has calculated how many people would be required to maintain genetic diversity and secure the success of the endeavor. William Gardner-O'Kearney helped Smith build the MATLAB simulations to calculate how many different scenarios would play out during interstellar travel and ran some simulations specially to show why the success of an interstellar mission depends crucially on the starting population size. Gardner-O'Kearny calculated each population's possible trajectory over 300 years, or 30 generations. Because there are a lot of random variables to consider, he calculated the trajectory of each population 10 times, then averaged the results.

A population of 150 people, proposed by John Moore in 2002, is not nearly high enough to maintain genetic variation. Over many generations, inbreeding leads to the loss of more than 80 percent of the original diversity found within the hypothetical gene. A population of 500 people would not be sufficient either, Smith says. "Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions." A starting population of 40,000 people maintains 100 percent of its variation, while the 10,000-person scenario stays relatively stable too. So, Smith concludes that a number between 10,000 and 40,000 is a pretty safe bet when it comes to preserving genetic variation. Luckily, tens of thousands of pioneers wouldn't have to be housed all in one starship. Spreading people out among multiple ships also spreads out the risk. Modular ships could dock together for trade and social gatherings, but travel separately so that disaster for one wouldn't spell disaster for all. 'With 10,000,' Smith says, 'you can set off with good amount of human genetic diversity, survive even a bad disease sweep, and arrive in numbers, perhaps, and diversity sufficient to make a good go at Humanity 2.0.'"
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## How Many People Does It Take To Colonize Another Star System?

• #### Why send the people? (Score:4, Interesting)

on Friday April 04, 2014 @02:31PM (#46663195)

If it's just genetic diversity you're worried about, why send the people themselves? It seems to me that sending that many people would be a massive over-expenditure of resources. Why not send much more manageable number of people to run the ship and build the initial settlement along with preserved genetic material for a massively larger population. Breed, predominantly, through artificial insemination for the initial generations until you are back to having the desired diversity in the actual living population.

• #### Re:Sure, but... (Score:4, Interesting)

on Friday April 04, 2014 @02:40PM (#46663291) Homepage
"By the time we have the tech to build a starship we can just ship out as many embryos as we can fit in a freezer. Job done."

Not quite.

The 18 years we spend now may be excessive but even figuring adulthood at 15 those embryos do not just magically hatch out as viable colonists. So while this might be a reasonable side-project to help a little, it's far from "job done."

Another way to cut down on the requirements is to deliberately pick the colonists based on genetics rather than assume a 'random' sample. I am normally against any sort of pseudo-racial quota system on principle, but in this one narrow case it would have a direct and clear justification. If instead of assuming random participants, you assume participants deliberately picked to be as genetically distant from each other as possible, you should be able to reduce the population requirements quite significantly.
• #### How many Earthworms? (Score:5, Interesting)

on Friday April 04, 2014 @02:41PM (#46663307)

To me, the question is not really how many people, but how many earthworms, and in general plants, bugs, birds, animals, etc.? At present, we really have no idea what is needed, nor in how much variation within each species, but I suspect the real answer will always be "more that we think."

• #### Starship Diversity? (Score:5, Interesting)

on Friday April 04, 2014 @02:49PM (#46663397)

On a vaguely related note: Assume you send N ships on this voyage. Do you send N copies of the same ship, and hope the design has no fatal flaw (while acknowledging the advantages of parts redundancy) . Or do you send N different designs in the hope that diversity of design is overall more reliable?

• #### Re:Sure, but... (Score:5, Interesting)

on Friday April 04, 2014 @02:53PM (#46663445) Journal

The point of exploring the stars will never be to "reduce the surplus population". That's not likely to be a real problem in any case.

The point is to broaden humanity's knowledge, perspective, and diversity. To make us, collectively, more than we are now.

But the stars are out of reach without some revolutionary new understanding of physics. The energy budget for interstellar travel is insane, assuming we want to get somewhere within a generation. It's far beyond workable fusion power needed for a starship: either some sort of warp drive, or antimatter fuel and a rocket with near-light speed exhaust.

The nice thing is, relativity means you can travel ridiculously long distances in subjective time and with an energy budget not much worse than going 100 light years. Humanity on Earth, not to mention the Sun, may be long gone when you get there, but you can visit other galaxies if only you had a magical power source.

• #### Re:Sure, but... (Score:5, Interesting)

on Friday April 04, 2014 @02:54PM (#46663469)

to be honest what is the use of this? Why do we want embryos on an other planet. Having to much people on earth won't be solved by sending embryos to other planet... As long as they can't send a large group of people in a short time to an other planet. This whole traveling to other planets is useless...

Redundancy. Overpopulation is not the reason -- that's a self-correcting problem.

Having all of humanity stuck on a single planet in a single solar system leaves mankind open to extinction from a rare planet ending or even a more rare solar system ending event. Though we probably need to get out of the Galaxy for true redundancy. I don't think there's any way to avoid the eventual end of the universe, whether its ends in a big freeze or big crunch...But we have a bit of time before that happens, so it can be left for future generations, as long as we don't end up killing ourselves or depleting our resources before we can get off the planet.

And who says, we didn't already do this? Send out lots of ships to other planets. After that we got some water problems, like Noah's story. After that only a few people survived, started to multiply and created a new civilization. Those people we send out there, are now living happily. And yes, there comes a bunch of embryo's again....

I'm pretty sure the fossil record is complete enough to rule out modern humans suddenly popping up from seeded embryos.

• #### Re:Sure, but... (Score:5, Interesting)

on Friday April 04, 2014 @03:09PM (#46663643) Journal

Reminds me of Tau Zero. [wikipedia.org] You can outlive the universe if you can squeeze yourself close enough to the speed of light...

• #### Math (Score:4, Interesting)

on Friday April 04, 2014 @03:10PM (#46663671)

Assuming the closest is even viable, which it probably isn't, 4.2 Light Years = 39735067984839.36 Kilometers. The fastest thing (only thing) man has sent out of our solar system is Voyager 1, which at its current speed, if it was pointed in the right direction would take about 73,775 years to reach the target. Considering you probably don't want to run into it at that speed, you will have to accelerate and decelerate. Which it doesn't have the fuel for (never mind its RTG energy source is only good for 60-80 years), but even if it did would roughly double the time to reach the intended target to about 147,550 years. OK well that's not quite true, it would only add an insignificant amount of time because not a lot of time was actually spent to accelerate in the first place. However in the example below where you do not coast for tens of thousands of years, and accelerate til the midway point and then immediately start to decelerate it would double whatever you speed VS distance is anyway.

Sure you could accelerate and decelerate much harder than that to get there much faster, approaching whatever value of c is currently capable at launch. However by any measure, unless some magic energy source and method of propulsion is devised, the required energy at least at today's standards would require carting around the hydrogen energy mass of our sun for the trip. Some other methods of insitu material gathering such as ram scoops picking up interstellar dust are as likely as the fiction, as again unless some dark matter type thing which is everywhere (presumably) is harnessed, the amount of mass available is pretty low, space as it turns out is pretty damn empty.

Not to mention the weirdness of relative time as one approaches c on a ship compared to Earth, as while it may take less than the 75k years voyager would, here on Earth many more years will have elapsed. As to how many, I have no idea, that is beyond my math calculating ability (as is generally most of what I have currently written I am sure will be pointed out).

Never mind trying to maintain a ship, machinery, technology, or even a society that long!

More likely colonization will involve self replicating and regenerating robotic ship carrying a genetic payload and an informational database (likely with a terra forming mission proceeding it). Which would be more like favorable seeding for similar evolution and life to occur, than an actual "colony". Then again, that would also require pretty adaptive programming and AI, which would likely mean we would probably be fertilizer for our robotic overlords petunia plants.

So I guess I am saying as a thought experiment it is sort of interesting, but at this point (or any really foreseeable point in our future), it is all a bit far fetched by even the loosest standards.

• #### 60k female embryos, 30k male (Score:4, Interesting)

on Friday April 04, 2014 @03:42PM (#46664099)
Generation ships are impossible** for humans, which will likely cause our extinction.

Although technically and logically, it is not an insurmountable problem. You need a small crew, 6 or 7 women per generation. A high number of frozen male and double that many frozen female embryos (which we will assume are viable forever, though we don't know).

All crew members birth one daughter. If one is not successful, one crew member births 2 daufghters.

They are raised to be the next generation of crew.

Many generations later, strict population control (through gender homogeny) 6 or 7 women will land on target planet (or more likely orbit it)

Exploratory team of males/females are raised during the last "transport" generation, then they are sent on a lander as a pilot program, meanwhile another generation of female crew is needed.

If pilot program is successful and either farming is not needed (if gatherer lifestyle is possible on destination) either send more landers, or land the craft and begin large scale birth-rate increases, with every female birthing 6 or more embryos as health allows.

While using up the rest of the embryos (which will be an exponential thing) Ease humanity into a reproductive lifestyle, as it will be culturally foreign to them.

**This requires so much space culture cooperation and "unethical" planning that humans would never do it. We are more likely to spend all of our natural resources to make a GIANT space ship that crashes and kills thousands of people instead, because of the "religion/culture" problem, which is unsolvable.
• #### Re:Sure, but... (Score:5, Interesting)

on Friday April 04, 2014 @03:47PM (#46664157)

I'm skeptical of those numbers anyway: There have been times [wikipedia.org] where the total number of humans was less than 40k with some speculation that there were as few as 2k for a while. That discounts, say, early settles to regions that then became the native people. How large a group traveled through the Bering Strait to the Americas? With current knowledge, we could screen the initial people for genetic diseases and organize breeding programs to maintain diversity, so we could probably be successful with even less.

Anyways, the ability to freeze bits (sperm, eggs, embryos) already exists and the projected lifetime of sperm at least would easily cover the journey plus the formative years. Heck, it's probably a better solution than legions of people even from a purely genetic perspective as you could probably better control radiation damage.

So that means genetics aren't really going to be as important as:
*) Builders - You aren't going to grandma's. You'll need able-bodies people to build you colony. Robots can help, but it's still going to require a decent crew. Even if you don't maintain this size group throughout the journey, you'll need it when you arrive, meaning the ship needs to have facilities for them to grow up in.
*) Parents - You need to keep people alive to teach new people what being people is. Books and other media will help, but you need a decent assortment to give an understanding of 'society' and prevent one bad egg over the 300 years from spoiling the bunch.
*) Society - Kinda tied to the last point, but you can't just have 10 people playing poker for 300 years. You need some ability to socialize, have friends, create, consume, etc.

I'd side with the anthropologist on this one: 150ish, a small village worth. Genetics are basically a solved problem and pretty much a footnote on the laundry list of problems that colonizing would face. Heck we don't even know if Proxima Centauri has a planet!

• #### Re:Sure, but... (Score:4, Interesting)

on Friday April 04, 2014 @04:07PM (#46664435)

extreme frontier living

What's extreme frontier living for people arriving by starship? They're going to have massive power sources and fully automated manufacturing facilities capable of making anything (including more automated manufacturing facilities), because starships need such power sources and probably such manufacturing facilities.

• #### Re:Meat Bags In Space == Impractical (Score:4, Interesting)

on Friday April 04, 2014 @05:34PM (#46665145)
So, something capable of FTL couldn't possibly hide from us and our barely evolved manipulation of the various spectrum technologies?

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