Some fun facts about evolution and sleep
Sep. 21st, 2020 01:35 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
garoteLately I've been listening to a really neat book called "Why We Sleep" and combining it with pieces of another book called "Sapiens" that so far appears to be about human evolution and the historical events that led us to be who and what we are. Just today I found that the books intersected.
The first book talked about how humans go through a very long adolescent development period relative to every other animal. We're basically helpless for about a decade, relying on parents and community to feed and teach us. Our brains are conditioned to require but also benefit from this process. In a nutshell, we're born with an extremely over-connected brain, and all the way up through puberty, our brain slowly prunes itself down in a process of optimization, during all the massive amounts of REM sleep we get. Half of the sleep time that babies get is spent in REM sleep. Once we're adults, the proportion of REM sleep settles down to about 20%. We still have lots of neuroplasticity, especially relative to other animals, but our major personality traits and mental habits are firmly established.
Neat stuff. The book also points out that our REM sleep is different from that of most other animals too, in terms of its intensity. When we enter REM sleep, our entire body is paralyzed except for a few vital functions, and this allows our brain to take much more of itself "off the hook" all at once. This sort of intensity is only possible because we've evolved to sleep on stable surfaces - e.g. the ground - instead of doing what all our other ape cousins do, which is sleep in trees to avoid predators and parasites. The version of REM sleep that their brains get is not as intense because they have to maintain their body awareness.
Today I was listening to the other book, and it pointed out that the human brain uses an absurd amount of energy relative to other organs in the body, relative to other animals: Our brains use up 25% of all the energy consumed by our body when we're at rest. Good grief! We are truly taking a unique approach to survival, favoring this thing so strongly.
The book also mentioned that to achieve our dominance as tool makers and projectile throwers, we had to have much more articulated hands, which made it awkward to walk on all fours like our ape forebears. Walking upright probably evolved first, so we could range farther more efficiently, and then that let our hands develop. It's very often the case like this in evolution: Some body part or behavior that was fixed in place because it was mandatory for survival suddenly becomes optional, so variations on it start appearing again in the population, and potentially grant an advantage. And in the even bigger picture, the long-term winners are lineages that can both vary, and stay consistent, in some subtle ongoing balance.
But to take advantage of those hands we needed big brains, which could only exist in big skulls. Women walking upright performed better with narrower hips, which meant a smaller birth canal. So how could humans get larger brains but still have narrower hips? By having babies with less-developed skulls and brains which then grew and fused during a drawn-out puberty. It takes a lot of subtle calculation to learn to throw rocks, and learn when to do it, and do similar tool-oriented things. Even without sophisticated language or complicated social structures, that would still favor larger brains. But if we go through a longer puberty, that means more time spent being dependent on others, and keeping your community convinced that you're a worthwhile investment is a competition, on a fundamental social level. Yet another reason to make that brain bigger. And if we're sticking together in trustworthy groups, it means we're far safer when we sleep, so our brains can intensify their REM cycles with less consequence. Now we have tool usage, social bonding, and the pressure to improve both, with a means to expand our brains. The stage is set for complex language and thought.
What's especially interesting to me here, is that like all things in evolution, what seems like a series of cause-and-effect stages that can be teased into a line is actually a crowded parallel process, involving overlapping tensions. The tension is between advantages and costs, creating a sort of dialing-in effect for the next generation, narrowing down near-infinite possibilities to arrive at the living result. For example, why can we keep track of about 100 personal relationships, but not more? Why do we take pleasure in gossiping about friends, family, neighbors, and celebrities, even though it doesn't create more food or shelter? Why is adolescence very long for us, but not even longer? Because It's all been dialed in by all these needs and counter-needs pulling at us...
Anyway, it was all very interesting and it made me think again about traveling and the way humans are able to form brief relationships and interact meaningfully with people that they've never met before, based on shared fictions -- ideas about things that are not physical in nature. The anthropologist in me is fascinated by the idea of doing experiments. That also made me think about physical and mental distance, and how that factors into relationships.
I've also been thinking lately about how I've changed as a person in relationships, over the years. Some things have been steady - like the curiosity that I always have, or the desire for dialogue and connection - and some things have changed, like my ability to have careful emotional discussions, my integration of my need for quiet alone time into my relationships, and my threshold for feeling insecure or threatened by certain situations. There have also been changes with a narrowing effect: Like, there are now situations or dynamics that I will just not engage with any more. Roles I will no longer play; tactics I will no longer use because they usually backfire. Like the brain doing REM sleep every night, there is always an ongoing calibration. Adding and also pruning. And I feel fortunate that I still have enough neuroplasticity to change and learn ... At least, according to these books.
It's wheels within wheels: The evolving human, with the evolving personality. The Leopard Cannot Change His Shorts, but the human can learn some pretty amazing new dance moves.
Anyway, back to the books...
The first book talked about how humans go through a very long adolescent development period relative to every other animal. We're basically helpless for about a decade, relying on parents and community to feed and teach us. Our brains are conditioned to require but also benefit from this process. In a nutshell, we're born with an extremely over-connected brain, and all the way up through puberty, our brain slowly prunes itself down in a process of optimization, during all the massive amounts of REM sleep we get. Half of the sleep time that babies get is spent in REM sleep. Once we're adults, the proportion of REM sleep settles down to about 20%. We still have lots of neuroplasticity, especially relative to other animals, but our major personality traits and mental habits are firmly established.Neat stuff. The book also points out that our REM sleep is different from that of most other animals too, in terms of its intensity. When we enter REM sleep, our entire body is paralyzed except for a few vital functions, and this allows our brain to take much more of itself "off the hook" all at once. This sort of intensity is only possible because we've evolved to sleep on stable surfaces - e.g. the ground - instead of doing what all our other ape cousins do, which is sleep in trees to avoid predators and parasites. The version of REM sleep that their brains get is not as intense because they have to maintain their body awareness.
Today I was listening to the other book, and it pointed out that the human brain uses an absurd amount of energy relative to other organs in the body, relative to other animals: Our brains use up 25% of all the energy consumed by our body when we're at rest. Good grief! We are truly taking a unique approach to survival, favoring this thing so strongly.
The book also mentioned that to achieve our dominance as tool makers and projectile throwers, we had to have much more articulated hands, which made it awkward to walk on all fours like our ape forebears. Walking upright probably evolved first, so we could range farther more efficiently, and then that let our hands develop. It's very often the case like this in evolution: Some body part or behavior that was fixed in place because it was mandatory for survival suddenly becomes optional, so variations on it start appearing again in the population, and potentially grant an advantage. And in the even bigger picture, the long-term winners are lineages that can both vary, and stay consistent, in some subtle ongoing balance.
But to take advantage of those hands we needed big brains, which could only exist in big skulls. Women walking upright performed better with narrower hips, which meant a smaller birth canal. So how could humans get larger brains but still have narrower hips? By having babies with less-developed skulls and brains which then grew and fused during a drawn-out puberty. It takes a lot of subtle calculation to learn to throw rocks, and learn when to do it, and do similar tool-oriented things. Even without sophisticated language or complicated social structures, that would still favor larger brains. But if we go through a longer puberty, that means more time spent being dependent on others, and keeping your community convinced that you're a worthwhile investment is a competition, on a fundamental social level. Yet another reason to make that brain bigger. And if we're sticking together in trustworthy groups, it means we're far safer when we sleep, so our brains can intensify their REM cycles with less consequence. Now we have tool usage, social bonding, and the pressure to improve both, with a means to expand our brains. The stage is set for complex language and thought.
What's especially interesting to me here, is that like all things in evolution, what seems like a series of cause-and-effect stages that can be teased into a line is actually a crowded parallel process, involving overlapping tensions. The tension is between advantages and costs, creating a sort of dialing-in effect for the next generation, narrowing down near-infinite possibilities to arrive at the living result. For example, why can we keep track of about 100 personal relationships, but not more? Why do we take pleasure in gossiping about friends, family, neighbors, and celebrities, even though it doesn't create more food or shelter? Why is adolescence very long for us, but not even longer? Because It's all been dialed in by all these needs and counter-needs pulling at us...
Anyway, it was all very interesting and it made me think again about traveling and the way humans are able to form brief relationships and interact meaningfully with people that they've never met before, based on shared fictions -- ideas about things that are not physical in nature. The anthropologist in me is fascinated by the idea of doing experiments. That also made me think about physical and mental distance, and how that factors into relationships.
I've also been thinking lately about how I've changed as a person in relationships, over the years. Some things have been steady - like the curiosity that I always have, or the desire for dialogue and connection - and some things have changed, like my ability to have careful emotional discussions, my integration of my need for quiet alone time into my relationships, and my threshold for feeling insecure or threatened by certain situations. There have also been changes with a narrowing effect: Like, there are now situations or dynamics that I will just not engage with any more. Roles I will no longer play; tactics I will no longer use because they usually backfire. Like the brain doing REM sleep every night, there is always an ongoing calibration. Adding and also pruning. And I feel fortunate that I still have enough neuroplasticity to change and learn ... At least, according to these books.
It's wheels within wheels: The evolving human, with the evolving personality. The Leopard Cannot Change His Shorts, but the human can learn some pretty amazing new dance moves.
Anyway, back to the books...
no subject
Date: 2021-07-22 07:31 pm (UTC)(credit for the thought goes to Richard Wrangham.)
no subject
Date: 2021-07-31 12:19 pm (UTC)I was always curious why people need love (as a cause for long term relationship) from biological point of view. (It obvious, I suppose, that biologically sex is the way of reproduction, sexual desire and pleasure are methods to make people reproduce themselves without sex education lessons and YouTube, but why do we need any long relations?!).
Now it make sense: as human kids require longer to get ready for normal life, they clearly benefit from both parents being nearby until the kids are more or less self-caring.
And, I guess, the love fades out when its function is over, and it's time to let the parents look for other partners - for the sake of getting more variability in their descendants.
Does it sound good?