Why has nothing evolved to not need sleep?

-RA-

An animal that does not need to sleep would be at a huge advantage over all other animals as animals are more vulnerable when asleep, so why are there none that have done that?

(i think i am correct in saying that all animals sleep)

jim mcnamara

Probably not correct - either of your assumptions.

-- more vulnerable

One view of sleep is that it EVADES predators. Example: human night vision is very poor compared to a lion. If humans sleep in a group, maybe in a tree, they are much safer than bumping around in darkness and walking right into the midst of a pride of lions to beome lion chow.


-all animals sleep (my definition of sleep is an altered brain state that shuts off or reduces incoming stimuli, not just a period when an animal waits for a meal to hop by):

example -
Animals like pit vipers - snakes that are active in darkness or daytime. They slow down only when they are digesting food, or temperatures are out range for functioning.

Otherwise, they are on the alert 24X7 when hunting. I do not know of any research that shows an altered brain state for snakes. By this I mean the reptilian equivalent of sleeping 'delta' waves, or REM sleep. Or even if snakes even have sufficient "higher" brain function to show altered brain states.

Anybody else know about snake EEG patterns?

-RA-

but they would be a lot safer if they were awake up the tree at night tham if they were all asleep up a tree. Animals are more vulnerable when they sleep, thats the very reason why they have to dig a burrow, or climb a tree in the first place.

thats similar as to how i would describe sleep, although i would tend to call it an altered state of conscious.

i should have been more specific, why do all mammals sleep even though they have all evolved separately.

mgb_phys

They all evolved from a common ancestor - that was probably nocturnal and hid in a burrow all day. If you are hiding in hole during the day it makes sense to reduce your energy demands by slowing down that calorie hungry brain so that when you do go out looking for food you don't need to find so much.

I would expect to see a reduction in hours slept as go from small to large animals.

jim mcnamara

-RA-

Okay, lose the tree. That's a non-sequitur response, you know.

Try a personal experiment.

Go to a field where you cannot see any electric lights closer than 100 yards or so. Go out on a dark moonless night.

Try to walk about. You will personally experience why some researchers think being awake at night and moving around was a bad idea for early humans. While you are stumbling around, pretend there are predators nearby. They can silently run 40mph, too. And you are on the menu.

You will also learn why lots of "primitive" people use walking sticks.

-RA-

point taken, although i think i'll leave the experiment for someone else to try!. I suppose that is a good reason for mammals with bad night vision; but what about animals that hunt at night, aswell as the day? they still sleep periodically.

i can understand that aswell, but i also cant see why we have to sleep to replenish our brains in the first place. An animal with a brain that 'replenishes' as it is use, and so would never need to rest, would be at a much bigger advantage than animals that do rest. I would have thought that over time some animals would have developed to not need sleep as it would be so advantageous.

I guess in an indirect way i am asking why exactly do animals need sleep so badly in the first place.

mgb_phys

It depends wether you sleep to replenish your brain (ie. allow chemicals to be built up or waste products to be removed ) or it is purely a low power state to save energy.

Cats sleep most of the time - to save energy, you might as well ask why they haven't evolved to chase and eat prey 24hours a day.

-RA-

what does sleep do out of those two options then?

i'm not sure if i'm saying this right, but i still cant see the real reason for sleep. If it was to replenish your brain why do you need to sleep for your brain to do that?, your brain builds up chemicals and removes waste products when you are awake aswell. If sleep is a low power state to save energy that implies that every animal has evolved to be inefficient at storing energy, and so has to sleep to save this energy. So if an animal evolved to become twice as efficient at using energy than its predecessors it should sleep for half the time. surely thats not correct?

Count Iblis

A long time ago on some science program I heard about a theory of how sleep is thought to have evolved. You have to go back way back to the pre-Cambrium. Just imagine that you have different primitive sea creatures that do not sleep. They eat and they use the energy from what they eat to find food move around etc. There is competition between different species. This drives the organisms toward the limit of their capabilities.

If you are a predator, then the prey will make sure you need to go beyond your maximum sustainable limit to catch them. This will then cause you to need a resting period of low activity to compensate for high activity periods.

Since sleep has evolved so long ago, it is basically hard wired into our system. When we are awake we function at a level that is simply not sustainable on the long run. You can think of undoing the necessity of sleep, but then the same dynamics of our early ancestors that led to the evolution of sleep will still apply: If you could somehow change your biology and go witout sleep and do theoretical physics 24 hours a day, then you could tweak your biological system a bit and obtain a system that can do physics much better for 10 hours but will need rest and sleep to recover.

TVP45

I think it is correct to say many scientists are unsure whether insects really sleep or not.

How do you know that not sleeping would be an advantage? At this point, we are still not clear on why we need sleep (except that almost all people who do not sleep will fairly quickly die) and so cannot assess what, if any, advantage sleep provides.

Proggle

Here's my personal take on it:

I think sleep evolved because it was, at a given point in evolutionary history, more energetically efficient than being awake all day. That means, it was better to go into a low-energy consumption state at night than trying to find food or mating in poor lighting conditions (keep in mind that this happened long before eyes evolved to their current level).

After this happened, a further advantage could be gained by those species that performed certain vital functions while sleeping, say tissue repair, allowing all energy to be focused to productive activities during the day. As the number of these "sleep activities" grew in number, it became increasingly difficult for future species to be able to "evolve" out of sleep. So the evolutionary adaptation for taking advantage of the fact that other species were sleeping was to become nocturnal, not to abandon it altogether.

TVP45

I see your point. Rather like trying to evolve flying once we had dense bones.

arildno

jim:
Why should a creature stumble about in the dark rather than just sit quietly up in a tree?
The crucial distinction is between
1. the resting, but awake (i.e, alert) creature and the

2. the resting creature fallen asleep (i.e, inattentive).

1. would be the best choice, from the perspective of natural selection.


However, as to the original question:

It is not enough for natural selection that some other state would be a better adaptation to the environment; it must also be an ATTAINABLE state.
(The gradient in evolution can't be too large).

scott_alexsk

Who says they would be stumbling about in the darkness, couldn't they simply evolve to see in the dark.

Proggle

To see in the dark you need:

- A lens, otherwise you simply won't gather enough light.
- A diaphragm (pupil), otherwise you'll go blind in daylight.
- A large number of sensitive photoreceptive cells.

If something like that had evolved instead of a mechanism for sleep, creationists would actually have a point.

Moonbear

Okay, I'm going to back up a few steps here. While everyone is speculating on the benefits/risks of not sleeping, there's a fundamental misunderstanding of evolution and natural selection in the opening post that needs to be addressed.

An organism cannot choose to evolve in a certain direction, or to acquire a particular trait. It doesn't matter how wonderful it might be, if a mutation that would permit it has never occurred, it can't happen.

However, as has been speculated above, it's possible that such a mutation HAS occurred, and turned out to NOT be adaptive, in which case it quickly disappeared from the gene pool again.

Proggle

The point I'm trying to make is that we may be so far down the path of depending on sleep that a mutation that disables it may not be feasible.

If an organism that doesn't sleep is born, it is very likely it will die, as systems that are supposed to function during that time are unlikely to have mutated to compensate for the change. This makes a one-step leap from sleep to no sleep extremely unlikely.

You may say "An animal could start sleeping less, and eventually abandon it." but if those intermediary states provide a disadvantage in survivability, even if the final state is better, the evolutionary path that leads that way will not be followed.