On Thursday, March 6, 2014 1:52:20 AM UTC, ghi...@gmail.com wrote: > > > On Thursday, March 6, 2014 1:37:48 AM UTC, Russell Standish wrote: >> >> On Wed, Mar 05, 2014 at 04:13:26PM -0800, ghi...@gmail.com wrote: >> > >> > On Wednesday, March 5, 2014 10:57:30 PM UTC, Russell Standish wrote: >> > > >> > > On Wed, Mar 05, 2014 at 02:26:50PM -0800, >> > > ghi...@gmail.com<javascript:>wrote: >> > > > > >> > > > So....you're saying its about resting the sensitive visual >> machinery? >> > > Why >> > > > not do that with an extra pair of eyes and a shift rota? That seems >> like >> > > a >> > > > legitimate challenge John, since it seems very doable, and the >> > > > benefit would be 24 hour action. Maybe even a pair of day eyes, and >> > > another >> > > > pair of night eyes. >> > > > >> > > >> > > Dolphins do something like this - they sleep one brain hemisphere at >> a >> > > time, so they don't drown in their sleep. >> > > >> > > -- >> > >> > >> > Very interesting indeed, and not something I knew. I suppose the >> > issues/questions would hinge on whether Dolphins are fully functional >> 24 >> > hours, or they have an advanced sleep mode. If the latter then the null >> > hypothesis as it were, would be whether that's an extension of the norm >> in >> > that all life has to keep the cardio vascular system going, and >> preserves a >> > degree of environment monitoring for basic threats. Sharks need to keep >> > swimming forwards not to suffocate. >> >> Not all species of shark. The ones we have around here are quite happy >> sleeping lying still in a cave, which is usually how you see them, as >> they're nocturnal. >> > I'd always defer to an aussie on sharks...but I'm curious how they get the > oxygen onto their gills. Could it be they exploit currents that certain > kinds of cave might produce? What happens when two windows are open on a > room sort of thing? Are those cave sharks quite small, out of interest? > Smaller fish have less oxygen demand...hence really little one don't seem > to need much of a sleep strategy for keeping the flow on the gills. > >> >> Re dolphins, the problem is that they cannot breathe underwater, so >> need to surface periodically to do so. Consequently, they need quite a >> bit of brainpower (essentially to be awake) to be active all the >> time. Fish (like sharks) do not face this problem, so can rely on >> autonomous "breathing" via their gills. >> > Could be, although larger fish would feasibly have oxygen needs > that couldn't necessarily be supplied by remaining stationary. > > >This all points to the necessity of sleep for some reason to do with > the brain. Liz listed a couple of plausible hypotheses. > > good ones as ever from Liz. But do you mean 'to do with the brain' as in > not to do with the conscious component? We're all agreeing about something > here, because I'm saying sleep is due to something in the brain too. > > > as an aside to this, from memory a lot of the 'living fossils' - forms alive today that don't seem a lot changed from Cambrian fossils, though very different in form, seem to have commonality in that they integrate movement and oxygen getting more closely. One model for this is the 'jet turbine' that gets movement from sucking water in one end and blowing it out the other. Squid/octopus do this I think, and then there's that little critter Davie 'crocket' Attenborough wheels out on the origin of life story...forget the name but you'd recognize it straight away. I thought sharks also had a solution this way that prevents them sucking water through their gills like fish. The survivability argument, I think, relates to some of the larger mass extinctions such as the Permian that saw periods of extreme oceanic hypoxia, or evidence thereof.
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