Science Reveals an Unexpected Difference Between Human and Mammal Brains
Could this small difference explain our superior intelligence?
Hiya!
You know, at some point, we all wonder why humans are the only advanced intelligent species around. We’ve searched everywhere we can for signs of other advanced life, but with no real success. Outer space, especially, has thus far proved a disappointment in this respect.
But thankfully, we have discovered a few species right here on Earth that possesses surprising cognitive capabilities — they just aren’t quite up to our level. But why is that? Why have no other Earthly species evolved intelligence as advanced as us? Finally, scientists think they have an answer, part of one at least. Turns out, there’s a small yet vital difference in our brains.
Brief Breakdown of Human vs. Animal Brains
As you probably know, humans aren’t all that different from many other animals regarding the structure of our brains, especially compared to other mammals. It’s why mice, for example, are good test subjects. The architecture and cells of a mouse’s brain are similar to ours, despite being completely different animals.
Even on a small scale, human brains are similar to other animals. Inside all mammals’ brains is a smaller and more complicated network of neurons using chemical and electrical impulses to communicate.
It was once thought our intelligence was due to us possessing more neurons than expected for our size, but this myth has been debunked. We actually have a relatively similar number of neurons compared to other mammals our size.
But a recent study confirms that ion channels in human brains are different than other mammals — at least the ten they tested. If you don’t know, ion channels control the flow of ions such as sodium and potassium while also helping neurons communicate by rapidly converting a neuron’s message into an electrical current and delivering it wherever it’s supposed to go.
How Humans Ion Channels are Different
Associate professor of brain and cognitive sciences, member of MIT’s McGovern Institute for Brain Research, and the study's senior author, Mark Harnett, and former MIT graduate student Lou Beaulieu-Laroche, unintentionally discovered something peculiar about the ion channels in humans compared to rats back in 2018.
They noticed rat neurons had a higher density of ion channels than neurons in the human brain. This surprised Harnett and Beaulier-Laroche because experts assumed that ion channel density was relatively the same across mammals. It was unusual enough of a discovery that they conducted a new study to see if this difference expanded to other mammals.
For the new study — published in November 2021 by Nature — Harnett and his team analyzed the neurons of ten mammals. In addition to human tissue removed from patients with epilepsy during brain surgery, they studied brain tissue samples from macaques, marmosets, rabbits, ferrets, guinea pigs, rats, mice, gerbils, and one of the tiniest known mammals, the Etruscan shrew.
An article by the Massachusetts Institute of Technology (MIT) about the study explains:
“In the tiny brain of the Etruscan shrew, which is packed with very small neurons, there are more neurons in a given volume of tissue than in the same volume of tissue from the rabbit brain, which has much larger neurons. But because the rabbit neurons have a higher density of ion channels, the density of channels in a given volume of tissue is the same in both species, or any of the nonhuman species the researchers analyzed.”
In other words, neuron size varies depending on the animal's size. Smaller animals have smaller neurons, and larger animals have larger neurons. But larger neurons have more and denser ion channels than smaller neurons from smaller animals. The result is that the density of ion channels is about the same in 9 out of 10 mammals they tested — humans were the only outliers.
Unlike the others, humans had a significantly lower density of ion channels than expected.
Harnett told MIT that it’s “surprising” that the density of ion channels increases as the neuron size does “because the more channels there are, the more energy is required to pump ions in and out of the cell.” But keeping the density relatively the same across species could mean the energetic cost of the ion channels stays about the same regardless of size. But this is what makes our ion channel density so interesting.
Harnett believes our brains may have evolved this lower density as a way to spend less energy on pumping ions. The brain could use this excess energy for something else, like more complex synaptic connections. But currently, what exactly our brains use this bonus energy for remains a mystery.
Though Harnett is on the case with plans to study where this energy is going, he also wants to know if mammals closely related to us also possess a lower density of ion channels. Perhaps some kind of gene mutation allows our brains this ability. Unfortunately, we’ll have to wait to find out.
Perspective Shift
We’re part of the animal kingdom; there’s no denying that. We have plenty in common with the natural world and are learning new similarities every day. But there’s also no denying that we’re different, too. Other animals may be intelligent, but none to the point of us.
But we may finally have a reason.
Theoretically, our brains found a way to decrease ion channel density, which allows our neurons a more energy-efficient communication method. The possible impacts this small change could have on our species are endless. Perhaps this allowed us to form language or boosted our pattern recognition. Maybe the extra energy went to developing our consciousnesses and curiosity. Whatever the result, I doubt we’d be who we are today if our brains maintained the status quo of high-density ion channels.
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