Re: Evolution of sleep

On May 17, 1:53=A0pm, William Morse <wdNOSPAmo...@xxxxxxxxxxxxxxxx>
wrote:
Darwin123 wrote:

=A0From memory and a quick check on the web, some sharks need to swim in
order to breathe - they don't have a good mechanism for moving water
over their gills when they aren't moving.
Some fish species, including a few shark species, need to swim in
order to breath. Mackeral, tuna, and white sharks (white referring to
family, not color) need to swim to breath. Most species do not.
The leopard shark may be one of these.
Wrong. The leopard shark is a large dogfish, not a white shark.
Dogfish do rest on the bottom occassionally.
I have never seen our leopard lie down to rest. However, aquarists
who have taken care of this animal for years tells me he spends a few
hours each night on the bottom of the tank, resting.

We also have two chain dogfish. This is a very small dogfish. It is
in the same family as a leopard shark. I have seen the chain dogfish
rest on the bottom.
Note: The chain dogfish tank is not well lit during the day. The
leopard shark tank is lit quite brightly during the day. I suspect
that is the reason for the difference.
The leopard shark doesn't do this with the lights on, so I never
saw him at rest. The chain dogfish doesn't know when it is "night," so
he rests when he wants to.

AFAIK even fruit flies need sleep. I agree that sleep can serve a number
of functions, but I don't think we yet really understand it well.

I agree as far as mammalian sleep. However, the development of
sleep probably took many small steps. I suggest that dormancy in fish
would be most likely to be the first step toward developing "sleep." I
think it is obvious that dormancy would most probably develop in fish
for the purpose of avoiding predators.

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