On Centauri Dreams, Alex Tolley writes about the challenges a generation ship would face.
He mentions one potential problem that I find particularly interesting, even though I’m not convinced of its seriousness: Genetic drift.
Over the quarter millennium voyage, there will be evolution as the organisms adapt to the ship’s environment. Data from the ISS has shown that bacteria may mutate into more virulent pathogens. A population living in close quarters will encourage pandemics. Ionizing radiation from the sun and secondaries from the hull of a structure damages cells including their DNA. 250 years of exposure to residual [galactic cosmic rays] and secondaries will damage DNA of all life on the starship.
However, even without this direct effect on DNA, the conditions will result in organisms evolving as they adapt to the conditions on the starship, especially the small populations, increasing genetic drift. This evolution, even of complex life, can be quite fast, as the continuing monitoring of the Galápagos island finches observed by Darwin attests. Of particular concern is the creation of pathogens that will impact both humans and the food supply.
In the 1970s, the concept of a microbiome in humans, animals, and some plants was unknown, although bacteria were part of nutrient cycling. Now we know much more about the need for humans to maintain a microbiome, as well as some food crops. This could become a source of pathogens. While a space habitat can just flush out the agricultural infrastructure and replace it, no such possibility exists for the starship.
The idea isn’t new. In Kim Stanley Robinson’s 2015 novel Aurora, microbial genetic drift is a major threat faced by a generation ship. As a geneticist, I’m used to thinking about evolutionary theory, and it’s not obvious to me how much of a problem microbial genetic drift would be, or even how to quantify the extent of the problem. Genetic drift is stronger in small populations like those on a starship. This could even be modeled. However, it may be impossible to predict how likely mutations that are deleterious to the ship’s entire ecosystem, and by extension its human passengers, are to arise and spread.
Nehaveigur 