Space settlement and human immune system evolution
I have had a manuscript on the back burner for many years about the North American biological genocide. Native American people tend toward an excellent Type 1 immune response over type 2. This helps them fight bacterial infections over viral. In South America and central America, this is still true, but the environment is less conducive to spread of common European viruses, particularly influenza. For instance, the Altiplano in the Andes is dry and has abundant UV, which prevents transmission of influenza and most cold viruses. Conversely, the jungle is wet and also prevents transmission of influenza, and relative isolation does the rest. Early records from the Plymouth colony describe total population death rates in native villages above 95% from diseases that were minor for the European settlers. This was the origin of the phrase, “manifest destiny” as it was presumed to be god clearing the land, thus it was manifest that the destiny of the settlers was to take the lands. Today, in North America, pure Native Americans are fairly rare. Virtually all survivors have some European genes, but some pure gene lines persist in outlying villages. With modern medicine, while they don’t do as well, they do well enough. We don’t see 50% population loss and up anymore among Native Americans.
Vaccines have saved Native Americans in the Southern Hemisphere, and are the first line of defense against the European disease pool. No human population is so deficient as to be unable to mount a type 2 immune response. It is just that this response is slower, and tilted toward type 1 in Native Americans.
It has been on the order of 10,000 to 15,000 years, and evolutionary pressure favoring people who survived bacterial wound infections, plus an absence of major viral diseases for Native Americans to develop this immune system that is better than most at handling wound infections, and worse at viruses. (Major viruses being smallpox, influenza, adenoviruses, cold viruses.) Does that mean it will take that long in space? Not necessarily.
One way to look at this is to say that a generation is around 20 years, so we are talking about 500 to 750 generations to get there. But this is not really correct. Strong evolutionary selection events, like smallpox, have left “scars of evolution” in Europe. Similarly, the same is true of North America relative to various European diseases. So selection events can imprint on populations rather quickly, in a matter of 2–10 generations.
Genetic drift can also cause major changes in small populations. I have a class exercise where we start with 4 parents, and all parents have one of two alleles, A and B. Flip a coin 4 times to see who mates with who. Then, flip a coin 8 times for each pair to see what alleles the children get. (Sometimes we flip a coin to determine sex first for each of 2 children. This adds a twist if, for instance, there is only 1 female who can only have 2 children. And we can talk about the impact of that, as well as matings on the side.) Do this iteratively for 4 generations, and you will see that one allele rapidly takes over the whole population. It does so by random chance.
Populations in space will tend to be small, and probably start with a fair amount of genetic diversity, which is good. Viruses die out in small populations. Even in our billions on earth, virus diseases that only infect humans can be wiped out. Others, like influenza, only persist because they are zoonoses that circulate in animal populations. So isolated space populations will tend to have little stimulation toward the robust anti-viral type 2 response that emphasizes antibodies and CD8 T-cells.
Populations in space will have significant bacterial challenges. On earth, we call what happens in quasi-closed environments “sick building syndrome’. Space environments will be sealed. Nothing goes in or out except people and cargo. No huge planetary atmosphere.
We humans need warmth and moisture. We shed bacteria and fungi constantly. There are always temperature differentials, and some surfaces will be cool where water will condense. So molds and biofilms will form on surfaces, and over time, spores and bacteria will invade the air. If the bacteria count rises high enough, then it tends to evolve into a pathogen, or a pathogen can evolve into a super-pathogen. This can happen rather quickly, because bacteria have short generation times. It has been documented to occur in hospitals in 6 weeks. There is the example also of the US Navy’s test of bioweapon dispersal by air in San Francisco in 1950. Serratia marcescens was not a known pathogen of any significance before this. But it is now.
In space, humans will be the primary host for any organism. For isolated populations, this will mean that either populations will evolve (culturally, and perhaps also pro-OCD) to be obsessive about cleanliness and keeping air systems filtered, or they will evolve immune systems that are able to handle high levels of mold spores and bacteria in the air.
I would say that it should take on the order of 20–100 years for the first serious disease outbreaks in closed space environments to make people cautious. Bacteria and fungi evolve faster than we do. In 10,000 years? People will have evolved and developed a wide range of methods to deal with it.