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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?

on Friday April 04, 2014 @02:33PM (#46663227)

A lot of people (not us Slashdotters, of course) have the misconception that other solar systems are right next door to ours. So I always illustrate it like this: The fastest spacecrafts we've ever built take about 9 years or so to go from Earth to Pluto. At that rate, they would take about 120,000 years to reach the next closest solar system. I also saw a great illustration once using a quarter (coin), to represent our solar system, and the next solar system being something like two football fields away.

• #### In the long run (Score:5, Informative)

on Friday April 04, 2014 @03:03PM (#46663585) Journal
Early human population dwindled to as few as 2000 individuals with most living in isolated pockets of a few hundred. Given enough time the population and genetic variability rebounded. Colonization of other worlds is most definitely a long-term project and while a bigger sample might give you better chances its probably possible with far fewer individuals.
• #### Re:Sure, but... (Score:5, Informative)

on Friday April 04, 2014 @03:55PM (#46664279) Journal
As it happens, those methods are big on drama and small on results. By way of example: here's Europe [wolframalpha.com], in millions, from the mid 19th century to more or less the present.

Notice the two tiny little dips around 1914 and 1939, and the effect (bugger all) if you take the longer view of, say, 1900-1975? That's two world wars, few genocides, and massive devastation of infrastructure. Not much population control per unit unpleasantness...(and if you think of this period as not especially 'sin'-pocked, maybe you would get along well with a certain old testament deity.)

Famine and plague are similarly good for painful, short-term, die-offs that just leave a bit of room below environmental carrying capacity that ends up being filled out by a new crop of poor fuckers within a generation or two. Disposable income and contraception, though? Now that will crater your birthrate more effectively, if less dramatically, than saturation bombing.
• #### Re:Sure, but... (Score:4, Informative)

on Friday April 04, 2014 @03:57PM (#46664299) Journal
Some sort of magic shield would be nice as well. There is mostly nothing but space in space; but there's nothing like colliding with it at the thick end of the speed of light to teach you that 'mostly nothing' and 'nothing' differ slightly.
• #### Re:Sure, but... (Score:4, Informative)

on Friday April 04, 2014 @04:09PM (#46664455) Journal

Sure, that's only ~5 TWH/ton. By comparison, the US as a whole consumes on average about 1 TW. If you spent 100 years of that time boosting, you'd need about ~5 MW of power generation (including 100 years of fuel) per ton of spaceship. So we're back to "revolution in physics".

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