
How do whales and dolphins sleep without drowning? - fanf2
https://www.scientificamerican.com/article/how-do-whales-and-dolphin/
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pcl
Wow, what an interesting article. Here's a great tidbit:

 _when diving, marine mammals ' blood travels only to the parts of the body
that need oxygen--the heart, the brain and the swimming muscles. Digestion and
any other processes have to wait._

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awkwarddaturtle
I wonder if this is why people tell you not to go swimming after you eat? I
remember my parents always telling me that. Would swimming/diving affect human
digestion?

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Patient0
Yes but it's a myth:
[http://www.medicinenet.com/script/main/mobileart.asp?article...](http://www.medicinenet.com/script/main/mobileart.asp?articlekey=47368)

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pcl
Somewhat-relatedly, an interesting story showed up here a little while back
about single-hemisphere sleep in humans:
[https://news.ycombinator.com/item?id=11545048](https://news.ycombinator.com/item?id=11545048)

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Scaevolus
Humans detect drowning by elevated CO2 in the blood. This means people walking
into downed weather balloons have no warning that they're running low on
oxygen before passing out and dying.

IIRC most aquatic mammals detect low oxygen directly instead, allowing them to
dive for over an hour without panicking. CO2 builds up in the blood, but they
can feel their oxygen levels directly.

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suneilp
Since oxygen plays a rather vital role in our functioning, I'm curious why we
can't detect low oxygen levels. Or perhaps we do detect them but only when
it's dangerously low. How has it been confirmed that we detect CO2 levels
instead of low oxygen?

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autokad
perhaps its because we and our ancestors do not have the environmental stress
to have that as one of our optimizations

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theodorejb
How could they have gradually evolved these abilities without drowning?

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overcast
I'm guessing, some lower form of life, pre dolphin must have mutated the
ability, but useless to them. Down the line, the dolphin was finally mutated,
still having the same.

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Waterluvian
If a mutation is useless it is unlikely to proliferate.

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carbocation
Fixation of a neutral allele within the population is proportional to its
frequency in the population. So, even something that is initially useless can
linger in the population, and even become fixed within the population. If that
neutral allele is lingering in the population at a low frequency and suddenly
becomes advantageous, there will subsequently be strong signals of selection
at that locus.

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tptacek
I wonder if this is a limiting factor for the development of their cognition.

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cetalingua
No, actually it seems to enchance their abilities, one recent study discussed
how dolphins can click and process received information while sleeping, or can
use sonar to search for fish, make decisions about echoes received, while
simultaneously whistling, communicating with others. This is a level of
complexity that is completely alien to humans.

[http://jeb.biologists.org/content/218/24/3987](http://jeb.biologists.org/content/218/24/3987)

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pbhjpbhj
What definition of sleep is being used here - full cognition (though in a
limited domain), motion, conscious response to external stimulii ... doesn't
appear to resemble my naive model of 'sleep', in what way is it sleep?

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cetalingua
Physiological definition- unihemispheric slow wave sleep, EEG measures each
hemisphere's activity, where the sleeping one shows low frequency, high
amplitude EEG readings.This is stage 3 sleep. Birds and manatees have it too.

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lngnmn
One hemisphere at a time.

