
Video Solves Mystery of How Narwhals Use Their Tusks - clouddrover
http://news.nationalgeographic.com/2017/05/drone-footage-narwhal-tusk-mystery/
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erikig
I wonder how they knew whether this is just one narwhal's or one colony's
modified behavior or the behavior of all narwhals'. Sea mammals are pretty
intelligent, who's to say that this one or this colony hasn't adapted some use
for their task that is restricted to just them?

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mannykannot
I doubt that this is the whole story, on account of females not having tusks.
If you take the position that the tusk is an adaptation to improve feeding,
which implies that it is sufficiently effective in that role for it to be
selected for, then you have to explain why the females' lack of the tusk is
not selectively disadvantageous.

My guess is that it was selected for a different reason (probably some form of
sexual selection), and has proven to be somewhat useful in hunting. Both the
possibility of sexual selection, and the possibility of features, selected for
their utility in one use, having uses for other purposes, were important
insights that allowed Darwin to defend his theory of natural selection against
critics (they also help defend Darwinism against the claim that it is a
fatuous tautology.)

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crygin
_then you have to explain why the females ' lack of the tusk is not
selectively disadvantageous._

No -- sexually dimorphic characteristics cannot be in competition.

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mannykannot
I am not suggesting that there is competition between males and females - both
are in competition with the rest of their world, especially with their prey
and others seeking the same prey. If one posits that the tusk was sufficiently
advantageous in helping males feed that it was selected for, that seems to
imply a corresponding disadvantage for tuskless females in their competition
with the rest of the world. If the female ancestors could feed just as well as
the males, then what was the source of the selective pressure on males alone?
Perhaps the males' sexual competition between themselves demands more food or
leaves less time to find it?

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GuiA
What if the mutation(s) that led to the tusk could only occur in males?

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ficklepickle
Fascinating! I wonder if they can move the tusk fast enough to cause
cavitation, which could stun the fish, making it easier to catch.

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B1FF_PSUVM
_" The tusk is a left canine tooth protruding from the heads of males and can
grow as long as nine feet. The right canine stays embedded,[...]"_

Where's the template for the Stross rejection note?

