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Why is there evolutionary pressure for the brain to shrink? We seem to have enough calories to feed our brains, and we're not beholden to some master species th

Why is there evolutionary pressure for the brain to shrink? We seem to have enough calories to feed our brains, and we're not beholden to some master species that needs to economize.

rackjack 5y ago
The brain itself is the evolutionary pressure. It is often repeated that the brain takes ~20% of our body's energy despite being ~2% of our body's mass. If there is no need to have a brain so large (due to a lack of predators) it is beneficial to shrink it.
- dymk 5y ago
  It's beneficial to lower the brain's calorie intake it if it results in higher reproductive fitness. But like GP said, we have plenty of calories, more than we've had compared to the entire history of humanity. So it doesn't naturally follow that lower calorie brains are higher fitness in 2021.
  - rackjack 5y ago
    "Although our brains were getting bigger progressively, around 70,000 years ago they plateaued, and have been shrinking ever since." From the article. 2021 is very recent. The article also discusses energy usage a little under the section "Fuel".
  - Fricken 5y ago
    There are no guarantees civilization won't collapse. The traits that were essential for our survival in the stone age aren't things we want to abandon. I'm a big fan of redundancy.
- Robotbeat 5y ago
  Beneficial how? Reduction in calories? We tend to have diseases of excess calories in the developed world now. If anything, the greater brain metabolism may actually help by burning some of those excess calories off…
  - rackjack 5y ago
    https://news.ycombinator.com/item?id=29033971 https://news.ycombinator.com/item?id=29033971
algebraically 5y ago
Because we no longer need to run away from predators and process information at the same rate we'd need to in a more wild enviornment. The survival pressures of our ancestral environment are no longer relevant. We've essentially destroyed and driven to extinction every other predator on the planet and now the only selective pressure is adaptation to the human created environment which is much nicer and simpler than the wilderness we came from. Simpler and safer environments make simpler brains and that's my best guess at why our brains are shrinking but I'm just an armchair scientist so it's better to ask the experts. The only remaining selective pressure is basically human predators, a.k.a. sociopaths.
- jacquesm 5y ago
  > and process information at the same rate we'd need to in a more wild enviornment If anything that rate of processing has gone up, not down.
  - algebraically 5y ago
    And most of it has been offloaded to computers (big data, deep learning, etc). I don't think we're going to have "mentats" any time soon.
    - jacquesm 5y ago
      You have this backwards. We are dealing with orders of magnitude more information than we did in ancient times, and we are required to remember a good chunk of it and to be able to recall and use it at a moments notice. Computers are a big factor in generating all of that information, even if they help process some of it the net effect is a huge surplus.
      - algebraically 5y ago
        I don't think I have it backwards. I don't remember anything or know much about the world in general terms. I just know and remember enough key phrases for google to give me the answers when I need them which requires very little cognitive effort on my part. [1] 1: https://www.psychologytoday.com/intl/blog/the-athletes-way/202110/does-googling-perpetuate-the-dunning-kruger-effect https://www.psychologytoday.com/intl/blog/the-athletes-way/2...
playpause 5y ago
“Use it or lose it” applies in evolution, because of energy usage, but also because of complexity. More features means more things to go wrong, more options for cancers, etc.
helge9210 5y ago
> Why is there evolutionary pressure for the brain to shrink? Less energy demand, I guess.

Why is there evolutionary pressure for the brain to shrink? We seem to have enough calories to feed our brains, and we're not beholden to some master species that needs to economize.

rackjack 5y ago

The brain itself is the evolutionary pressure. It is often repeated that the brain takes ~20% of our body's energy despite being ~2% of our body's mass. If there is no need to have a brain so large (due to a lack of predators) it is beneficial to shrink it.

dymk 5y ago
It's beneficial to lower the brain's calorie intake it if it results in higher reproductive fitness. But like GP said, we have plenty of calories, more than we've had compared to the entire history of humanity. So it doesn't naturally follow that lower calorie brains are higher fitness in 2021.
- rackjack 5y ago
  "Although our brains were getting bigger progressively, around 70,000 years ago they plateaued, and have been shrinking ever since." From the article. 2021 is very recent. The article also discusses energy usage a little under the section "Fuel".
- Fricken 5y ago
  There are no guarantees civilization won't collapse. The traits that were essential for our survival in the stone age aren't things we want to abandon. I'm a big fan of redundancy.
Robotbeat 5y ago
Beneficial how? Reduction in calories? We tend to have diseases of excess calories in the developed world now. If anything, the greater brain metabolism may actually help by burning some of those excess calories off…
- rackjack 5y ago
  https://news.ycombinator.com/item?id=29033971 https://news.ycombinator.com/item?id=29033971

algebraically 5y ago

Because we no longer need to run away from predators and process information at the same rate we'd need to in a more wild enviornment. The survival pressures of our ancestral environment are no longer relevant. We've essentially destroyed and driven to extinction every other predator on the planet and now the only selective pressure is adaptation to the human created environment which is much nicer and simpler than the wilderness we came from. Simpler and safer environments make simpler brains and that's my best guess at why our brains are shrinking but I'm just an armchair scientist so it's better to ask the experts. The only remaining selective pressure is basically human predators, a.k.a. sociopaths.

jacquesm 5y ago
> and process information at the same rate we'd need to in a more wild enviornment If anything that rate of processing has gone up, not down.
- algebraically 5y ago
  And most of it has been offloaded to computers (big data, deep learning, etc). I don't think we're going to have "mentats" any time soon.
  - jacquesm 5y ago
    You have this backwards. We are dealing with orders of magnitude more information than we did in ancient times, and we are required to remember a good chunk of it and to be able to recall and use it at a moments notice. Computers are a big factor in generating all of that information, even if they help process some of it the net effect is a huge surplus.
    - algebraically 5y ago
      I don't think I have it backwards. I don't remember anything or know much about the world in general terms. I just know and remember enough key phrases for google to give me the answers when I need them which requires very little cognitive effort on my part. [1] 1: https://www.psychologytoday.com/intl/blog/the-athletes-way/202110/does-googling-perpetuate-the-dunning-kruger-effect https://www.psychologytoday.com/intl/blog/the-athletes-way/2...

playpause 5y ago

“Use it or lose it” applies in evolution, because of energy usage, but also because of complexity. More features means more things to go wrong, more options for cancers, etc.

helge9210 5y ago

> Why is there evolutionary pressure for the brain to shrink? Less energy demand, I guess.