

Animals That Taste Only Saltiness - wormold
http://nautil.us/blog/the-animals-that-taste-only-saltiness

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tieTYT
> When a mutation came along that made the receptor not work, that animal was
> just as likely to survive as one that didn’t have the mutation.”

Then shouldn't there still be a chance of having the mutation because nothing
is selecting for or against it? Instead it seems the entire species can't
taste sweetness so the gene was removed. Why would that happen? I don't know
of any other explanation than, "there is an advantage to not being able to
taste sweetness".

EDIT: I removed "50/50" from my question. That wouldn't be the right
percentage.

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protonfish
If the mutation only occurred once, yes. But if there is no selection pressure
against a broken gene, every time it mutates it will enter the gene pool until
the working version eventually disappears completely. (After many years, of
course.)

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whatshisface
But wouldn't there be an equal chance of the mutation reversing itself? This
is true in digital transmissions, why not in DNA?

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dllthomas
A gene isn't one bit.

For starters, there are four nucleotides in DNA (A, C, G, and T). Simplifying
our model of mutation to "a flipped bit" where mutation takes takes a
nucleotide to another one with equal likelihood, and only one nucleotide in
that position makes it functional, there is a 3/3 chance that a mutation
breaks it but only a 1/3 chance that a subsequent mutation fixes it.

Next, there's the fact that every gene is a sequence of _many_ nucleotides.
The odds that the next mutation of the same gene would happen in the same
place is low.

Finally, many mutations don't take the "flipped bit" form we assumed above.
Repetitions, insertions and deletions also happen, and may be even less
reversible (deletion of a meaningful portion would be exceedingly unlikely to
be recreated by chance - what provides the information about what should have
been there?).

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jeltz
There is no mention of smell in the article. What if dolphins use their sense
of smell instead?

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tiglionabbit
Dolphins can't smell.

They retain all of the mammal sense-of-smell genes for smelling in air, but
they are corrupted by random mutations. None of them function anymore.

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jeltz
Thanks! That would have been useful information for them to add to the
article. I assume Hyenas still retain their sense of smell though.

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walruscop
Interesting. Makes me wonder how we evolved our taste buds.

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baddox
I don't know the details, but it's fairly easy to imagine a series of small
steps that could occur via random mutations, where each small step offered a
slight fitness advantage over individuals without the mutation.

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SoftwareMaven
Isn't that just the definition of evolution?

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baddox
It's a key problem many people have with understanding (and in some cases,
believing) evolution. The classic example is the complex human eye.

