Brain body size evolution

[RonO]

https://www.sciencedaily.com/releases/2024/07/240708101004.htm

https://www.nature.com/articles/s41559-024-02451-3

The Nature article is open access.

The authors claim that they have developed a model for the relationship
between brain and body weight for mammals and the evolutionary
trajectory for different lineages. With this model they can identify
lineages that do not conform to the usual brain size evolution
relationship to body weight. As pretty much every other study has
indicated humans have evolved bigger brains for their body weight and
primates have a higher rate of brain size increase. Some lineages have
lower brain size to body weight than expected. As you might expect
these are the largest mammals. They speculate that brains take a lot of
energy to maintain, and that there is likely selection against larger
brains at some point in body size increase. Population sizes for large
mammals have to be smaller because it takes more food to maintain
individuals. The estimate that I have seen is that it takes 80% of our
energy production to run our brains. If you have smaller brains you
could maintain larger populations. Hunter gatherer populations were
probably restricted by our brain's energy needs. With the poorer
agricultural diet our brains actually decreased in size as our
population increased. We could maintain much larger populations on the
same amount of territory, but it wasn't a diet amenable to supporting
large brains.

Ron Okimoto

[Athel Cornish-Bowden]

Post by RonO
https://www.sciencedaily.com/releases/2024/07/240708101004.htm
https://www.nature.com/articles/s41559-024-02451-3
The Nature article is open access.
The authors claim that they have developed a model for the relationship
between brain and body weight for mammals and the evolutionary
trajectory for different lineages. With this model they can identify
lineages that do not conform to the usual brain size evolution
relationship to body weight. As pretty much every other study has
indicated humans have evolved bigger brains for their body weight and
primates have a higher rate of brain size increase. Some lineages have
lower brain size to body weight than expected. As you might expect
these are the largest mammals. They speculate that brains take a lot
of energy to maintain,

Does that require speculation? Surely we *know* that the brain uses a
lot of glucose.

Post by RonO
and that there is likely selection against larger brains at some point
in body size increase. Population sizes for large mammals have to be
smaller because it takes more food to maintain individuals. The
estimate that I have seen is that it takes 80% of our energy production
to run our brains. If you have smaller brains you could maintain
larger populations. Hunter gatherer populations were probably
restricted by our brain's energy needs. With the poorer agricultural
diet our brains actually decreased in size as our population increased.
We could maintain much larger populations on the same amount of
territory, but it wasn't a diet amenable to supporting large brains.
Ron Okimoto

[RonO]

Post by Athel Cornish-Bowden

Post by RonO
https://www.sciencedaily.com/releases/2024/07/240708101004.htm
https://www.nature.com/articles/s41559-024-02451-3
The Nature article is open access.
The authors claim that they have developed a model for the
relationship between brain and body weight for mammals and the
evolutionary trajectory for different lineages.  With this model they
can identify lineages that do not conform to the usual brain size
evolution relationship to body weight.  As pretty much every other
study has indicated humans have evolved bigger brains for their body
weight and primates have a higher rate of brain size increase.  Some
lineages have lower brain size to body weight than expected.  As you
might expect these are the largest mammals.  They speculate that
brains take a lot of energy to maintain,

Does that require speculation? Surely we *know* that the brain uses a
lot of glucose.

The speculation is for the second half of the sentence. There may be
some point where the brain to body weight ratio can't keep up with the
standard ratio of correlated increase, and smaller relative brain size
would be selected for to reduce the energy load. I do not know what
they think now, but when I took biology and comparative anatomy the
notion was that you needed larger brains to control the larger body
mass, and that is why brain size showed the correlation with body
weight. The high energy demands of the brain may mean that at higher
body weights you may have to select for smaller relative brain size to
reduce the energy demands of the brain. For humans we selected for
bigger brains that allowed us to collect more calories from the
environment. When we subjected ourselves to a poorer diet by taking up
agriculture we selected for smaller brains.

Animals can obviously select for more efficient brains. Bird brains are
amazingly efficient in terms of what they can do for their size, and
octopus brains are likely equivalent. Avians and molluscs can do a lot
with small brains. Avians needed smaller brains because they needed to
reduce the energy load and weight to fly, and octopus are cold blooded
and needed their brains to work under those conditions.

Ron Okimoto

Post by Athel Cornish-Bowden

Post by RonO
 and that there is likely selection against larger brains at some
point in body size increase.  Population sizes for large mammals have
to be smaller because it takes more food to maintain individuals.  The
estimate that I have seen is that it takes 80% of our energy
production to run our brains.  If you have smaller brains you could
maintain larger populations.  Hunter gatherer populations were
probably restricted by our brain's energy needs.  With the poorer
agricultural diet our brains actually decreased in size as our
population increased.  We could maintain much larger populations on
the same amount of territory, but it wasn't a diet amenable to
supporting large brains.
Ron Okimoto

[Ernest Major]

Post by RonO
https://www.sciencedaily.com/releases/2024/07/240708101004.htm
https://www.nature.com/articles/s41559-024-02451-3
The Nature article is open access.
The authors claim that they have developed a model for the relationship
between brain and body weight for mammals and the evolutionary
trajectory for different lineages.  With this model they can identify
lineages that do not conform to the usual brain size evolution
relationship to body weight.  As pretty much every other study has
indicated humans have evolved bigger brains for their body weight and
primates have a higher rate of brain size increase.  Some lineages have
lower brain size to body weight than expected.  As you might expect
these are the largest mammals.  They speculate that brains take a lot of
energy to maintain, and that there is likely selection against larger
brains at some point in body size increase.  Population sizes for large
mammals have to be smaller because it takes more food to maintain
individuals.  The estimate that I have seen is that it takes 80% of our
energy production to run our brains.  If you have smaller brains you
could maintain larger populations.  Hunter gatherer populations were
probably restricted by our brain's energy needs.  With the poorer
agricultural diet our brains actually decreased in size as our
population increased.  We could maintain much larger populations on the
same amount of territory, but it wasn't a diet amenable to supporting
large brains.

The number floating around the web is that the brain (2% of body mass)
consumes 20% of resting energy usage (and presumably a lower proportion
when performing hard physical labour).

Elsewhere I find it said that the heart and kidneys use more energy per
gram than the brain, and the liver and spleen combined use more energy
that the brain does.

Post by RonO
Ron Okimoto

[RonO]

Post by Ernest Major

Post by RonO
https://www.sciencedaily.com/releases/2024/07/240708101004.htm
https://www.nature.com/articles/s41559-024-02451-3
The Nature article is open access.
The authors claim that they have developed a model for the
relationship between brain and body weight for mammals and the
evolutionary trajectory for different lineages.  With this model they
can identify lineages that do not conform to the usual brain size
evolution relationship to body weight.  As pretty much every other
study has indicated humans have evolved bigger brains for their body
weight and primates have a higher rate of brain size increase.  Some
lineages have lower brain size to body weight than expected.  As you
might expect these are the largest mammals.  They speculate that
brains take a lot of energy to maintain, and that there is likely
selection against larger brains at some point in body size increase.
Population sizes for large mammals have to be smaller because it takes
more food to maintain individuals.  The estimate that I have seen is
that it takes 80% of our energy production to run our brains.  If you
have smaller brains you could maintain larger populations.  Hunter
gatherer populations were probably restricted by our brain's energy
needs.  With the poorer agricultural diet our brains actually
decreased in size as our population increased.  We could maintain much
larger populations on the same amount of territory, but it wasn't a
diet amenable to supporting large brains.

The number floating around the web is that the brain (2% of body mass)
consumes 20% of resting energy usage (and presumably a lower proportion
when performing hard physical labour).
Elsewhere I find it said that the heart and kidneys use more energy per
gram than the brain, and the liver and spleen combined use more energy
that the brain does.

That is what it seems to be. For some reason I recalled it to be 80%.
Maybe I just transposed the percentages.

The web claims that kidneys use twice as much energy per gram as the
brain (>400 kcals/kg per day, supposed to be the same as for the heart).
One estimate for the heart was 440 kcals/kg. The brain uses around
200 cal/g per day (200 kcals/kg). The the two kidneys only weigh around
400 g total, and the heart weighs around 300 g, while the brain weighs
1,300 g, so the brain uses more energy than your kidneys or heart that
use the most energy per gram.

A paper I found had resting energy needs.
https://www.sciencedirect.com/science/article/pii/S0959438822001623

Brain 21%, Kidney 8%, Heart 8.9%, Skeletal muscle (36% of total mass,
while the brain is 1.9%) 21.2%.

Ron Okimoto

Post by Ernest Major

Post by RonO
Ron Okimoto

[erik simpson]

Post by Ernest Major

Post by RonO
https://www.sciencedaily.com/releases/2024/07/240708101004.htm
https://www.nature.com/articles/s41559-024-02451-3
The Nature article is open access.
The authors claim that they have developed a model for the
relationship between brain and body weight for mammals and the
evolutionary trajectory for different lineages.  With this model they
can identify lineages that do not conform to the usual brain size
evolution relationship to body weight.  As pretty much every other
study has indicated humans have evolved bigger brains for their body
weight and primates have a higher rate of brain size increase.  Some
lineages have lower brain size to body weight than expected.  As you
might expect these are the largest mammals.  They speculate that
brains take a lot of energy to maintain, and that there is likely
selection against larger brains at some point in body size increase.
Population sizes for large mammals have to be smaller because it
takes more food to maintain individuals.  The estimate that I have
seen is that it takes 80% of our energy production to run our
brains.  If you have smaller brains you could maintain larger
populations.  Hunter gatherer populations were probably restricted by
our brain's energy needs.  With the poorer agricultural diet our
brains actually decreased in size as our population increased.  We
could maintain much larger populations on the same amount of
territory, but it wasn't a diet amenable to supporting large brains.

The number floating around the web is that the brain (2% of body mass)
consumes 20% of resting energy usage (and presumably a lower
proportion when performing hard physical labour).
Elsewhere I find it said that the heart and kidneys use more energy
per gram than the brain, and the liver and spleen combined use more
energy that the brain does.

That is what it seems to be.  For some reason I recalled it to be 80%.
Maybe I just transposed the percentages.
The web claims that kidneys use twice as much energy per gram as the
brain (>400 kcals/kg per day, supposed to be the same as for the heart).
 One estimate for the heart was 440 kcals/kg.  The brain uses around
200 cal/g per day (200 kcals/kg).  The the two kidneys only weigh around
400 g total, and the heart weighs around 300 g, while the brain weighs
1,300 g, so the brain uses more energy than your kidneys or heart that
use the most energy per gram.
A paper I found had resting energy needs.
https://www.sciencedirect.com/science/article/pii/S0959438822001623
Brain 21%, Kidney 8%, Heart 8.9%, Skeletal muscle (36% of total mass,
while the brain is 1.9%) 21.2%.
Ron Okimoto

Post by Ernest Major

Post by RonO
Ron Okimoto

There are some people's brains that don't work as hard as that.