Comment by outworlder | Hacker News Reader

Comment by outworlder | Hacker News Reader

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> The brain truly is a system with terrible service availability. On average, after running for just 16 hours, it must be offlined for 8 hours to run maintenance tasks such as "scrub", "garbage collect", "trim", and "fsck".

It's a trade-off. The brain is about as large as it can be while making birth possible. It already uses a lot of energy(2% of body weight, 20% of energy consumption). We also need it to be working at peak performance when we are doing activities.

A background 'scrub' task to keep it working 24/7 would probably use more energy (require more food and heat dissipation 24/7), possibly require a larger area (for redundancy, similar to how dolphins can sleep one hemisphere at a time and have really large brains). An alternative would be to slow down processes enough so that those tasks could happen constantly.

And then our day/light cycles helped select for this approach. Until recently there wasn't much one could do (safely!) at night.

> The brain is about as large as it can be while making birth possible.

Is that true? The 'birthable' parameter limits only two dimensions. Could the brain evolve to a larger size in a third dimension?

https://www.youtube.com/watch?v=OS1cj-zk4ac

Maybe there is some other limitation, such as distance between neurons? Signal strength?

> The brain is about as large as it can be while making birth possible.

I wonder if it had been beneficial to have larger brains, we'd have evolved to support that. Diminishing returns maybe or just a local maximum we didn't get out of?

Beneficial kinda just means "leads to more procreation" right?

So if bigger brains meant people reproducing more, our brains would get bigger to the point that most births are cesarean or something.

I do wonder what happens when we eventually evolve to a point where we can't survive without more and more advanced technology.

A lot of people who would have died off before reproducing 200 years ago now don't, which is of course incredible for us. But what are effects of that 100/1000 years down the line?

Presumably we'll have plenty of more immediately pressing issues over that time frame.

Check in with various farm animals, they are already there.

It is interesting from a space-faring species perspective. By the time we can embark to other planets/asteroids our biology might require us to lug around significantly more technology just to survive.

So how evolution works is that a feature needs to have an evolutionary advantage, but the specimen must also not die. So there are two adversarial pressures here, carefully balancing each other in a mammal species that already has one of the highest birth mortality rates of both mother and child. If heads were any larger, it would create a proportional amount of negative evolutionary pressure by both direct and indirect death (of the mother) at birth.

Interestingly, there seem to be some indications showing that human interventions by modern technology already show clear evolutionary trends: https://pmc.ncbi.nlm.nih.gov/articles/PMC5338417/

Humans might eventually evolve to not even being able to be born naturally anymore at some point.

That's a fascinating thought. As people with larger brains are more successful in life and more likely to have children*, mortality rates for natural births would increase, and over time we would evolve to become dependent upon modern technology.

The continued existence of our species would become dependent upon continued civilisation. A dark age could kill us, or at least cripple the population.

*how true is this? Uni-educated people tend to have lower fertility rates.

"Children? With these economic conditions?"

"There's no way we could have a child now. Not with the market the way it is, no."

https://www.youtube.com/watch?v=sP2tUW0HDHA

> As people with larger brains are more successful in life and more likely to have children*

> *how true is this? Uni-educated people tend to have lower fertility rates.

In the U.S. university education depends mostly on mommy and daddy's wallet size, not brain size.

I dont have data but I’d assume that wallet size is correlated to brain size

That would be quite a claim and I certainly wouldn't assume it!

If maternal mortality were the only issue, evolutionary pressure would also favor women with wider hips/birthing canals. After all, we see hyper intelligent individuals at the current brain size, it's clearly possible to get more processing power in there but there doesn't seem to be much reproductive benefit.

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