Why Did Sleep Evolve?

Why Did Sleep Evolve?


Hey guys! I’m Jon and WELCOME to Respect Your
Intellect! From pretty much any angle we look at things, we see evidence of evolution in
the traits we look at. We can look at animals today and see features that either no longer
seem to function because they’re just part of their ancestry, or they have different
functions altogether. Some animals have eyes that no longer work and serve no purpose,
some whales have hip bones that serve no purpose, some snakes have leg bones buried in some
of their muscles, and we ourselves have a lot of features that no longer serve any purpose;
like our appendix, wisdom teeth, goosebumps, as well as many others. In many cases when
it comes to evolution, we can somewhat intuitively make predictions of something we have yet
to find because it’s often easy to know what will make something more fit to survive and
pass down their genes to their offspring. However, sleep seems to be completely counter-intuitive
in this regard because it seems to be a state of total vulnerability to predators. So why
did sleep evolve? Hit that subscribe button and lllet’s get started! [Intro] There’s something generally agreed upon by
most people today and that’s that sleep has regenerative effects. Sleep is something that’s
mystified researchers for many decades and is still today being researched heavily. We
now know that sleep re-energizes the body’s cells, it clears waste and toxins from the
brain, it solidifies important memories while discarding the unimportant ones, it supports
learning, helps our immune systems, and it regulates our mood, our appetites, and our
libido. With that said, a lot of researchers hypothesized
that these things are the reason why sleep evolved but there’s really no evidence linking
sleep’s regenerative effects with evolution. The regenerative effects that we just listed
could easily be accomplished by much shorter sleeping periods; yet, we sleep about a third
of every day, all at once. It also doesn’t explain why sleeping patterns are so different
across the animal kingdom. Some animals can sleep for entire seasons, others sleep the
majority of every day, and others barely sleep at all; yet they would all benefit from a
bit of daily regeneration. The way that sleep works for us is that our
eyes go through a state of melatonin production when it gets dark. This melatonin then travels
up to the brain and attaches to our neurons which essentially signals our body that it’s
time for sleep. Once our eyes start catching light again, the melatonin production is stopped
and we regain control. Even though we seem to know what sleep does and how it works,
there’s still a lot of questions that need answering. One of the things we do, in an
effort to understand sleep better, is spend a lot of time studying different organisms
and their sleeping habits; one of which is fruit flies. They seem to show very similar
habits to what we do as humans. When we interrupt their sleep cycles, for example, it causes
them to have longer rest periods afterwards to try and make up for the lost sleep. They
also show all the signs of jet lag when we start messing with the light they receive
at different times of the day. Even though this research seems promising
for helping us understand the effects of sleep, it still doesn’t really try to address the
question of why sleep evolved in the first place. For that, we need to study organisms
that give us a link much further up the ancestral evolutionary tree. One of the organisms that
we found that could answer some questions is a marine worm who’s name I’ll just put
on screen: “Platynereis Dumerilii”. So a study was started at the European Molecular Biology
Laboratory in Germany to study everything about it. The study proposes that melatonin
production, and therefore sleep, evolved about 700 million years ago in a common ancestor
between many different species and these little marine worms. When the worms are about two days old, they’re
essentially a ball-shaped larva that’s lined with tiny hairs that makes them swim. They’re
also lined with cells on top of them that make the same light-catching proteins that
we make in our eyes to switch melatonin production on and off. During the day, when the larva
catches light, melatonin production is stopped and the little hairs beat back and forth to
make them swim up. As night sets in, melatonin production turns on and the hairs stop moving
when the melatonin attaches to the neurons that control the beating hair, causing the
larva to sink. So every day, these little larvae are moving up and down in the ocean,
following the cycle of the day; in the same way we do. We also tested them for jet lag
and found the same thing we experience ourselves; and just like the fruit flies do, as well.
The fact that the melatonin network is so strikingly similar between these worms and
humans suggests that we have a common ancestor. It’s so similar in fact that even the way
in which melatonin takes over the brain is the same. The melatonin attaches to neurons
and causes them to start emitting a regular rhythm of bursts. With these neurons busy
doing their own thing, they’re no longer relaying information to the rest of the brain. In our
case, it’s our thalamus that shuts down while in the worm, it’s the part that controls the
beating hair. If you weren’t aware, our thalamus is the part of our brain that’s responsible
for relaying motor and sensory signals to the rest of our brain; which explains why
you don’t really move much while you sleep and why you don’t really wake up from little
noises. Alright so we covered a lot about what sleep
is, how it sets in, and even when it might have first evolved. We even talked a bit about
the lack of evidence with the claims that it evolved “because” of its regenerative effects.
So if it didn’t evolve due to its regenerative effects, the question still remains: what’s
our best hypothesis today as to why sleep evolved in the first place? After all, every
trait we look at in evolution exists because it contributes to the fitness of that organism
to survive and pass on their genes to the next generation. Sleep however, is a state
of total helplessness that doesn’t seem to benefit our fitness for survival, at least
not at first glance, if the regenerative effects are set aside. The first thing we need to look at is what’s
common among all the species that sleep and what we find is that even though every species
that sleeps have different cycles from each other, they’re mostly always aligned with
their food source’s activity cycle. When you take this into account, it really does make
sense that preserving energy when there’s no food around would benefit our survival.
Another thing that seems to mostly always be aligned is that species sleep mostly during
the times of the day that they’re the most vulnerable to predators. This is also something
beneficial for a species because you’re essentially hiding and regenerating while you’re the prey
and using up your energy reserves while you’re the predator and there’s a lot more food around.
So between a creature that doesn’t sleep and takes high risks for very little food and
a creature that avoids risk and uses up its energy when there’s a very high chance for
success, it’s not hard to imagine that the latter will outlive the former. One thing is pretty certain in any case and
that’s that if sleep evolved, it’s because it’s beneficial for our survival; simply because
every old trait is. It’s only in our very recent history that we actually have enough
control over our environment to allow the unfit to survive; otherwise nature would simply
take its course and eliminate the quote unquote “weak”. So even if, at first glance, it seems
like the helplessness that sleep comes with would diminish our chances for survival, it
actually has the opposite effect by keeping us out of harm’s way when there’s little benefit
for the risk and allowing us to concentrate our energy reserves only at times when we
have a lot of food around with little risk. We still have a lot of research to do and
a lot of questions to answer when it comes to sleep but I, myself, am happy we’re starting
to eliminate some of the old hypotheses that aren’t holding up to scrutiny and coming up
with better ones that explain more while being more in line with what we actually observe
all around us. I hope you enjoyed this video and I also wanna
thank my patrons on Patreon for supporting the channel. I really appreciate the support!
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10 comments

  1. I think sleep, or any period of less activity, is innate in pretty much in all species. There is even a circadian rhythm seen in plants and trees. It doesn't seem much of a reach to say that this is evolutionary, and necessary for life of any type.

  2. Would love to see you delve much deeper into this subject. I have never experienced regular sleep patterns and very rarely sleep more than two hours at a time.

  3. A fascinating subject Jon.
    Birds seem to sleep half a brain at a time, like cetaceans. Swifts sleep in flight. πŸ™‚

  4. I will give some useless info. i have worked a number of 24 hour races. So it's interesting when you do enough and if you are like me (where I need to be up for all 24 hours and then give another 6-12 hours extra) that it's a challenge. What i find is that when something like the 24 hr of Daytona starts at 3:30pm, it really is a struggle to stay awake. When it started at noon, not so much. What is the common opinion for everyone is that making all the way to sunrise is not that hard, about an hour after sunrise, then you feel spent. After that its a struggle to keep going and when you need to make decisions, you need a a few others so you know you are not losing your marbles.
    In 2008 I worked with this team to win the Dayona 24 in Rolex GT. You'll see it as the #70 Mazda RX8. I was part of the three man strategy team. Here's the last 3 hours.
    https://www.youtube.com/watch?v=MjygRGbNYDI

  5. Fascinating video. I didn't realize the eyes created melatonin and sent it to the brain's neurons. I wonder what would happen if a person's eyes did not create melatonin. I would have to think they would still feel sleepy, so there must be something else biologically that is happening to tell the brain it needs to sleep than whether or not the sun is up…or did I misunderstand?

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