From an evolutionary perspective, sleep might seem like a dangerous waste of time. When
animals slumber, they're less responsive to their surroundings and potentially more vulnerable to predators. And of course it's hard to reproduce when you're fast asleep. Many researchers assume that sleep must offer some adaptive advantage that more than makes up for its downsides. But what could that benefit be? Despite a great deal of research, there's no consensus.
That's because it's the wrong question to ask, according to Jerome Siegel, a neuroscientist at the University of California, Los Angeles. In an editorial published online this week in Nature Reviews Neuroscience, Siegel argues that sleep researchers have gotten off track in hunting for a universal benefit to sleep. In Siegel's view, the sheer diversity of sleep behavior, physiology, and neurochemistry argues against the idea that sleep confers the same benefit on all creatures.
A few examples:
*The big brown bat, one of the sleepiest animals known, dozes more than 20 hours a day. Giraffes sleep only about 4 hours.
*Migrating birds and newborn killer whales appear to forgo sleep for several weeks without having to make up for it later.
*REM sleep has been found in all terrestrial mammals tested (but not in dolphins and other cetaceans) and in birds (but not in reptiles, fish, or amphibians).
*Humans secrete more growth hormone during slow-wave sleep. Rats and dogs secrete growth hormone while they're awake.
*Male humans and rats experience erections during REM sleep. For male armadillos, erections occur only during non-REM sleep.
Instead of searching for a common thread through this confusing and contradictory jumble, Siegel argues, researchers should be thinking more about why different species sleep the way they do. He thinks it comes down to being active when it will do the most good. The brown bat, for example, wakes up at dusk just when the moths and mosquitoes it feeds on are most active. If it woke up any earlier, Siegel explained to me in a phone interview, it would risk attacks from agile raptors with keen daytime vision. If it stayed awake any later, fewer insects would be flying around. "Their awake time is exactly appropriate for their needs," Siegel says.
He thinks researchers should consider sleep as part of a continuum of inactive states found throughout the plant and animal kingdoms. Such periods of inactivity are adaptive mainly because they optimize the timing of particular behaviors (or other energy expenditures in the case of plants). Like a maple tree dropping its leaves or a bear settling in for a winter hibernation, sleep is just another way of making sure organisms spend their resources wisely, Siegel says. Thus, the reason sleep is so maddeningly diverse is that animals have such diverse ways of making a living. So, if you want to understand why an animal sleeps the way it does, you first have to understand what it does while it's awake. Siegel asserts.
"This strikes me as perhaps the most sensible thing I've seen written in a long time on the topic of what sleep is all about," says Ralph Greenspan, a neurogeneticist at the Neurosciences Institute in San Diego, California. The paper suggests to Greenspan that sleep arose first in some simple form and then gradually became more complex as more complex nervous systems evolved. His lab is just getting started on a project to investigate this idea more directly by looking for sleep-or something like it-in a handful of primitive organisms including jellyfish, which have a simple nervous system; Trichoplax, a simple marine creature with no nervous system; and single-celled Paramecium. They'll also examine several genes whose expression has been found to rise or fall during sleep in fruit flies and mice. "The main question is whether sleep requires a complex brain or whether sleep requires a brain at all," Greenspan says. Either way, the findings should provide interesting fodder for the discussion of what sleep is and how it evolved.
—Greg Miller
Genes Sleep Time May Chart Their Evolution Circumstances
Add This To The Lifehood Of Genes Case
A. From "Circadian clockwork takes unexpected turns"
http://www.sciencenews.org/view/generic/id/48177/title/Circadian_clockwork_takes_unexpected_turns
Some neurons in the brain’s master clock fall silent in the afternoon. The unexpected finding prompts scientists to rethink how the clock works.
- deals with "brain’s master clock", "molecular-clock gears" and "natural circadian clock".
- finding is “actually very shocking".... at least two different populations of neurons, each having its own ( sleep ) rhythm...
B. This finding should prompt researchers to search and assess also non-peer-reviewed background info,
and to rid themselves of the ancient mantras like "brain’s master clock", "molecular-clock gears" and "natural circadian clock".
Sleep is innate for genes simply since during their genesis and early history, when they were independent not-yet-genomed-nor-yet-celled organisms there was not yet biometabolism and they were active ONLY during sunlight time, their ONLY usable energy.
The neural system, like ALL biological systems and processes of multicell organisms, originated and evolved from the life-culture of cooperative communities of monocell organisms, over a very long period during which biometabolism has evolved to furnish usable indirect-solar-energy.
It is probable and possible that just as the later evolution of biometabolism involved various formats of symbiosis so the way-back protoneural network evolution in monocell organisms communities involved symbiosis or inclusion of genes from different locations on Earth, genes with different innate sleep time.
Or it is also probable and possible that a neural network section regularly requires a daily PM cleanup that cannot wait until 2 AM, at which time the genes normally "retire" and melatonin signals intercell maintenance time, and the genes in this section evolved the required additional or changed sleep-time, see:
http://www.sciencenews.org/view/generic/id/46762/title/From_Axons_to_Identity__Neurological_Explorations_of_the_Nature_of_the_Self_by_Todd_E._Feinberg
It is probable and possible...
Dov Henis
(Comments From The 22nd Century)
Updated Life's Manifest May 2009
http://www.the-scientist.com/community/posts/list/140/122.page#2321
Implications Of E=Total[m(1 + D)]
http://www.the-scientist.com/community/posts/list/180/122.page#3108