Evolution of sleep

In a recent article in Discover Mag

http://discovermagazine.com/2009/apr/22-new-theory-about-why-sleep-mainta=
in-immune-system/?searchterm=3Dsleep

Researchers did a study on sleep and disease, and while there data is =
correct their interpretation is wrong. They have left out a =
statistically significant factor in their explanation for the =
observations.

Infectious disease requires a vector of transmission, that is they =
require close contact with an infected individual. The process of =
contagion is a required component in the transmission of all viruses, =
parasites and bacterial infections.
Organism that are awake and mingling with other organisms and =
interacting with the environment meet this important criterion. =
Organisms while awake are exposed organisms. On the other extreme =
Organisms while asleep are less likely to encounter pathogens.
During a 24 hr period an organism that is awake twice as much as another =
organism would show statistically on average more incidence of disease =
[probably twice the incidence].
One could take this argument to an extreme and ask, would an animal =
sleeping 24 hrs a day show less incidence of disease than one that is =
awake 24 hrs? The answer is of course yes.
In fact we do have organisms that sleep 24 hrs a day, and we call it =
hibernation.
If we do a study on hibernating animals, we would find minimal disease =
during this phase. In this case we would not wrongly claim that =
hibernation evolved to prevent disease?

You could just as easily do a study on injuries and find that organisms =
injure themselves significantly less while asleep than when they are =
awake. But would we conclude that sleep evolved to prevent injury?=20

Another example ,,,,, what do humans do when we face a disease epidemic?
We Quarantine!
We Quarantine to break the vector of transmission [less exposure]. Sleep =
has the same effect, it isolates with less exposure, but it is side =
effect of sleep not the main reason for sleep.

There is little doubt that sleep benefits the immune system, [if not =
just because in this quiescent state it is not being assailed and can =
regroup in numbers of host protections]. But sleep did not evolve for =
disease protection but rather disease protection is an exaptation where =
the immune system has found utility within the confines of sleep [which =
evolved for another purpose].=20

Processes like the brain reorganizing connections between neurons, =
consolidating memories, and synthesizing proteins and cholesterols that =
are important in tissue repair, have certainly found utility within =
sleep but these are exaptations and certainly not the reason for it.

It is also a myth that sleeping animals increase their risk of =
predation, quite the opposite is true, but that is another topic. [see =
below]

For an interesting conjecture on the evolution of sleep see;
http://home.i-zoom.net/~wgilmour/cosmoevo/Sleep.html
...





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