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Recently I've been imagining living on a terraformed Venus in a distant future. I've a pretty good idea of how this can be done, having gone through many articles on how to terraform venus, so my question isn't related to that portion. Instead, I have some questions about what sort of genetic adaptations might be useful after the terraforming.

https://terraforming.fandom.com/wiki/Venus_Simulation

Using that as a guide, I figure my Venus has about 5 bars (slightly less than 5 earth atmospheres) of atmospheric pressure. Humans, obviously, usually live at slightly more than 1 bar (or 1 atmosphere specifically) of pressure. So, what sort of genetic adaptations might we have given humans to colonize this high-pressure environment? What other adaptations might be useful to a planet that something like 86 days of the year blanketed in clouds?

Assume that the peoples in this story don't have anything beyond iron age tools at their disposal, so adaptations should primarily be genetic.

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    $\begingroup$ What's the composition of the atmosphere? This is kind of important. 5% oxygen, 15% nitrogen, 0.5% water vapor, 0.01% carbon dioxide and the rest helium will work without any genetic adaptation. $\endgroup$ – AlexP Aug 30 at 12:18
  • $\begingroup$ The 5% oxygen mixture you give is most likely, because presumably the fewer alterations made the easier it would be to get the initial colonists there. Beyond that would we need anything more for a 5 bar atmo? $\endgroup$ – Benjamin Wandio Aug 30 at 12:22
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    $\begingroup$ Partial pressure of nitrogen is also important; humans do not like high partial pressures of nitrogen. Partial pressure of carbon dioxide is very very important -- more than 0.01 atm is not at all good for humans. $\endgroup$ – AlexP Aug 30 at 12:34
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    $\begingroup$ "86 days of the year blanketed in clouds" is something anyone in London or Bruxelles would call "a year of excellent weather" $\endgroup$ – L.Dutch - Reinstate Monica Aug 30 at 12:58
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    $\begingroup$ @L.Dutch: Pretty certain Londoners would complain about it being too sunny... $\endgroup$ – Joe Bloggs Aug 30 at 13:18
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Assuming an atmospheric composition similar to Earth's (~20% oxygen, 80% nitrogen), with an atmosphere at 5 bar, your partial pressure of oxygen is just over 1 bar, which is below the toxicity limit (not much below, but safe enough). Nitrogen narcosis might be an issue (your atmosphere is equivalent to 55 m depth, which is right on the border for nitrogen narcosis for humans -- some will narc at that pressure, some won't). One of your genetic adaptations would need to be a higher tolerance for dissolved nitrogen in the body, in order to avoid narcosis. If you want scuba diving to be a thing once technology advances, you'll need to work extra hard on this one. You'd probably also want to reduce hematocrit (red blood count) which would, I think, raise the oxygen toxicity limit by reducing oxygen transport.

Other than that, once the cloud layer is cleared up enough and the anti-greenhouse layer is in place, your Venerians will need adaptations for the approximately 5x UV flux they receive due to being closer to the Sun. Gravity isn't enough different to matter, so that should cover what's needed for survival.

The other issue with Venus is its rotation -- it's actually got a sidereal day longer than its year, though because of its retrograde rotation the solar day is only 116.75 Earth days. Adaptations to this might be similar to bears hibernating (they'd be awake three months, then asleep one, near enough, with some period -- a week or two -- of activity in darkness, just as we have a few hours of waking time in darkness most of the year), or might be along the lines of enabling more effective sleeping in daylight and improved night vision for activity during the roughly two month nights.

If loss of technology went so far as to eliminate mechanical clockwork (i.e. below about 14th century level, when at least town clocks were fairly common), timekeeping would depend on what modifications had been made to adapt to a four month day-night cycle. If people slept one month in four, during darkness, they'd keep time by the sun and stars, as was done by most people for most of history before the invention of practical mechanical clocks (water clocks required a lot of maintenance, and other early timekeeping methods, like sand glasses or candle clocks, didn't work well for periods longer than a few hours).

The movement of the stars at night, at roughly half the rate of the sun's daytime motion, is still sufficient to see the passage of the two months of darkness -- a star that was on the meridian when first visible (after a week-long twilight) would be nearing the eastern horizon by dawn (which occurs in the west).

With the lowest eccentricity of any Solar planet, and a near-zero axial tilt, Venus would lack seasons as we know them. Instead, temperature (and heat-driven weather) would tend to increase throughout the daylight hours, and decrease through the two months of night, giving a sort of seasonal variation amounting to a month of spring morning, a month of afternoon summer, a month of evening autumn, and a late-night winter the fourth month. It's unlikely the cooling period of the night would get cold enough for snow or surface ice, except possibly near the poles, but if the anti-greenhouse layer is working as it should, it shouldn't get above "hot summer" temperatures -- around 35-40 C -- by the end of the afternoon summer.

Weather itself would be similar to Earth's weather, except that there is virtually no Coriolis effect, so cyclonic storms would be unfamiliar. No hurricanes, no tornadoes, no dust devils. A thermal current that, on Earth, would cause an anticlockwise whirlwind might cause a vortex spinning in either direction (depending on the air currents already present), or one with very weak or no spin at all.

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    $\begingroup$ Venusians, surely? Venerians sounds like they should have some horrible disease... ;-) +1 either way! $\endgroup$ – Joe Bloggs Aug 30 at 13:17
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    $\begingroup$ Actually, Venerian is the correct form, according to my reading. Yes, from the same root as venereal disease (Venus was the goddess of love, including sex). $\endgroup$ – Zeiss Ikon Aug 30 at 13:19
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    $\begingroup$ "Venerian" would be the Latin derived form. "Venusian" would be the English derived form. If this answer had been written at some point before 1950-1960 then one could make a case for using Latin derivation; but, alas, a classical education being no longer in fashion, I'd say that today most people would expect "Venusian" as the adjective derived from "Venus". I shudder to think of the day when I will see "Marsian". $\endgroup$ – AlexP Aug 30 at 13:45
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    $\begingroup$ @ZeissIkon: never occurred to me that was the root, but now you mention it it’s obvious. Huh. You learn something new every day. $\endgroup$ – Joe Bloggs Aug 30 at 13:47
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    $\begingroup$ @BenjaminWandio Expanded w/ details about weather, seasons, timekeeping, and sleep patterns. $\endgroup$ – Zeiss Ikon Aug 31 at 15:58

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