Taldain is a tidally locked planet in a binary system where one of the suns is a weak white dwarf enclosed in a ring while the other a shiny blue-white supergiant. As a result in one hemisphere is always night-time and the other lives a perpetual day.

The star that faces the darkside emits lots of UV light, and the dark-side life has evolved to make use of this light: plants do photosynthesys with that light and it seems the inhabitants are mostly black skinned to get protection from that light and have fluorescent teeth and nails.

However, the day side should also receive lots of UV light and it seems only logical that the same environment pressure should make for a similar adaptation in life. I can see why the fluorescent nails are of no use, but why dark skin is not predominant in the day-side too? Would specially appreciate WOB (Word of Brandon).

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    I was wondering that too. One thing is that there are two stars: the sun, the Dayside one, may just not emit that much UV light, although I would think it should. Tidal locking means that the Dayside just won't see the white dwarf that emits all that UV light. Another is that latitude matters: we could be seeing a more northerly latitude on the Dayside, indeed perhaps the only habitable area, or perhaps not.
    – Adamant
    Commented Jul 16, 2019 at 23:51
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    I will clarify that there are two stars, but my point was that even a regular star emits lots of UV specially if it's always day.
    – Ram
    Commented Jul 17, 2019 at 0:02
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    The entirely speculatative theory I've seen on various forums is that Autonomy/Bavadin altered the genome of the Daysiders to make them resistant to UV without needing to darken their skin. That's an unsatisfying explanation to me because it just moves the question up a level and forces you to ask why he felt the need to do that when there's a perfectly good natural adaptation to handle it.
    – Alarion
    Commented Jul 17, 2019 at 0:47
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    She - Autonomy is female. Most of the time.
    – Adamant
    Commented Jul 17, 2019 at 2:28
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    It's certainly quite possible that it's just that the part of Dayside we are seeing, which might even be the most inhabited part, is far from the equator. People won't really be getting twice the UV exposure, since they'll stay sheltered during sleeping hours. Anyway, Autonomy is in (is?) the sun, so who knows what kind of spectrum it's emitting.
    – Adamant
    Commented Jul 17, 2019 at 2:37

1 Answer 1


Because Brandon decided.

Strumienpola (paraphrased): Why don't Daysiders have darker skin?

Brandon Sanderson (paraphrased): It's just how genetics on Taldain have played out. They should be darker-skinned, but there's always some randomness to genetics, so this is just how they played out in this case.


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    Hmmmm. So he's saying that it's due to mutation? That's certainly possible: see albinism for an extreme example of how mutation can produce people with much paler skin than the general population. For that to work for a whole population and a pretty disadvantageous non-dominant mutation, though, you'd have needed a bottleneck in the distant past, where everyone ended up descended from relatively few people. I think this would be very improbable.
    – Adamant
    Commented Jul 17, 2019 at 19:21

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