What makes the human brain so special? Other animals show remarkable intelligence especially
when we compare the size of the brain to that of the human. So is there some fundamental difference
in the brain of humans compared to that of other mammals? Pinning down this difference has been
very difficult but now a team of researchers from MIT have found a remarkable difference
and it's all to do with the flow of ions... Let's dive in and find out more.
Up until recently, no significant differences had been observed between the brains of mammals
and those of humans. A team of researchers from MIT have discovered that compared
to other mammals, human brains have a much lower number of neuronal channels
that allow the flow of ions such as calcium, potassium, and sodium.
The flow of these are responsible for the electrical impulses that allow neurons to
communicate with each other. This could mean an energy saving and might allow the human brain to
operate more efficiently, diverting resources to more complex cognitive functions. This was
a surprise given previous studies had not found strong evidence that human neurons were special.
Back in 2018, a study on the comparison of rat brains and human brains found the first clue in
uncovering this difference. The study had examined dendrites, which are the branching structures at
the tips of nerve cells through which the brain's electrical signals are received via ion channels.
Once the signal is received the dendrite generates what is called an action potential,
which transfers the signal onwards. When they compared the dendrites of rats and humans they
found that the human dendrites had a much lower density of ion channels compared to the rats.
This new research expanded this initial study to include additional species including, shrew,
mouse, gerbil, ferret, guinea pig, rabbit, macaque. They discovered that the ion channel
density increases with neuron size and the only exception to this rule was the human brain!
It is likely that in the other mammals the difference was to maintain ion channel density
across a range of brain sizes. So the shrew has a higher number of neurons than a rabbit
in a given volume of brain, the density of ion channels in that volume was consistent. And this
means that the building plan is consistent across the different mammalian species with the cortex
keeping the numbers of ion channels per unit volume the same across all the species. This in
turn means that for a given volume of cortex the energetic cost is the same for the ion channels.
The glaring exception would appear to be the human brain but it would be fair to point out
that the study only covers mammals that are significantly smaller than humans but it is
worth noting that the macaque is often used in research as a model for the human brain.
So why would this have developed in the first place? The researchers suspect an
evolutionary trade-off was possible for humans. It takes energy to pump ions through dendrites.
So if it can minimise the ion channel density and still perform the same function
it would be able to deploy the energy savings elsewhere.
Maybe in the development of more complex synaptic connections or more rapid action potentials.
But this still does not really address WHY this might have happened. If other
mammals were able to survive with an inefficient brain what task did humans
have to overcome that required the building of additional connections in the brain
that mammals did not have? Is this in anyway related to the obsession of observing the heavens?
Even in quotes cavemen drew pictures of constellations in some of their artwork. Even
the earliest civilisations seem to pop up with already a deep-rooted desire to study and follow
the heavens. Did our earliest ancestors live through terrible cataclysms that forced them to
have to start working collectively and looking to the heavens to try and predict the coming of the
next disaster? And then finding some way to pass this information on from generation to generation?
The paper does not speculate on when these changes might have occurred in the human brain
as there are no brain samples of our ancestors to look at. A surprising fact about humans today
is that our brains are smaller compared to the brains of our Pleistocene ancestors.
Why the brains have reduced has been a big mystery for anthropologists.
In a new study, they analysed a dataset of 985 fossils
and modern human crania and found that human brain size increased in size 2.1 million years ago
and then again 1.5 million years ago but then decreased in size about 3000 years ago.
Most people are aware that humans have unusually large brains compared to our body size.
The reduction in human brain size around 3000 years ago was quite unexpected.
So they set about trying to understand why the brain might have decreased in size by studying
ants? Although ants and human societies have taken very different routes in terms of social evolution
there are important aspects that they were able to study and were still applicable to humans.
And it once more comes back to energy. Brains use a lot of energy, and smaller brains
use less energy. They postulate that the decrease in brain-size was due to an
increased reliance on collective intelligence. The storing of knowledge externally
meant that this could be shared across the group, not each individual.
Now did the more efficient brain lead to a shrinking in size? It's odd in the first article
that they never discuss this as a possibility instead focus on the fact that the brain could
do other things, make other connections, and yet it is a known fact that the human brain
has shrunk in size? And if we consider that human brains did shrink and that this was solely due to
a collective intelligence what does this mean for those hominids that had a brain 20% larger?
The idea that they were not able to think collectively is a little absurd
there is plenty of evidence that complex societies did exist more than 3000 years ago but the idea
that they were more intelligent than we are is not something anthropologists would ever consider.
Generally, it is considered that brain size increase is related to intelligence
and that this can increase over time for any given species.
Decreasing brain sizes is also observed in some species but understanding why this might
happen is much harder as they do not actually have the brain to examine, only the skull.
The Yuga cycle talks about 4 different ages. As we move from one age to the other humanities
moral and physical state slowly decreases until a cataclysm ends it and resets it.
There is some debate as to how long each of these ages actually lasts and whether they end and reset
or end and reverse. The idea that man has fallen from a golden age is something that is mirrored
in other cultures as well. Could there be some truth to this idea not just in terms of a cyclic
cataclysm but also physiological changes to human caused by changes in our external environment?
This would then imply that we should also see changes to the brain sizes
in other mammals and in particular related to any known cataclysms!
In a study looking at brain sizes, they discovered that changes in brain size occurred after two
cataclysmic events in Earth's history. Dated to 66 million years ago and 23-33 million years ago.
After these events, the researchers noticed a dramatic shift in brain-body scaling
in rodents, bats, and other carnivores. Although it is also important to point out that in general,
the brainsizes for these mammals did not decrease from those points onwards.
There are many questions that both pieces of research throw up, are they related to each other
or not? Were the larger hominids' brains already more efficient? Why would the human brain shrink
if prior to this they were already living and working in complex societies?