
Clues from a Somalian cavefish about modern mammals' dark past - dnetesn
https://phys.org/news/2018-10-clues-somalian-cavefish-modern-mammals.html
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lordnacho
This is absolutely fascinating. It seems there's a very common (among living
creatures) visible light dependent DNA repair mechanism, the discoverer got
the Nobel for it. This fish, along with modern mammals, has lost it,
suggesting that mammals at some point evolved in the dark.

But I don't see in my searches where it mentions that mammals don't have this
mechanism anymore? You'd think the Wikipedia would mention it.

~~~
wahern
"The photolyase mechanism is no longer working in humans and other placental
mammals who instead rely on the less efficient nucleotide excision repair
mechanism."
[https://en.wikipedia.org/wiki/Photolyase](https://en.wikipedia.org/wiki/Photolyase)

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cing
This reminded me of a nice article about how blindness evolved in the Mexican
cavefish,
[http://seedmagazine.com/content/article/pz_myers_on_how_the_...](http://seedmagazine.com/content/article/pz_myers_on_how_the_cavefish_lost_its_eyes/)

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pvaldes
There is something here that we must be missing. Mammals aren't the only
animals living in the dark.

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gnulinux
Mammals don't live in the dark. Some of them do but there are non-nocturnal
mammals too. The idea in this article is that this is an evidence that mammals
might have evolved in the dark (such as in caves).

~~~
pvaldes
The idea in this article is that mammals and a blind cyprinid have evolved in
the dark and this explains the lost of this mechanism (evidence that mammals
might have evolved in the dark). It was not necessary to keep a defense
against UV that plants, fungi and other animals still conserve. The part that
troubles me is the "but the other creatures still have it".

UV rays do not enter well in the deep water layers so marine fishes living
under 60m deep shouldn't have any use for this mechanism. Why mammals had lost
it and those fishes still keep it?

I would suggest to read the former statement as "but most other creatures are
still untested for the mechanism".

Or maybe we are missing other possible explanations here. I'll add a different
hypothesis: "because (or this is evidence that?) placentate mammals have
evolved in the dark of a womb and other animals have external embryos (like
kangaroos) or have delicate eggs".

My hypothesis would be that the real purpose of this mechanism is protecting
the embryo development when even a small punctual UV damage could trigger a
cascade of much more serious consequences. This would explain why marsupials
and other fishes still need it but diurnal placentates not.

Crocodyles, Platypuses or marine turtles that dig nests in the soil still keep
this mechanism?.

