Scientists Used Human Genes to Make Monkey Brains Bigger, and It Worked

By putting human genes into monkeys, scientists managed to stimulate the growth of their brains. 

Even though chimps are our closes living relatives, their brains are three times smaller than ours.

It is presumed that the size of our brains makes us the dominant species over our primate cousins.

But what if we could increase their brain’s size? Would it make them smarter?

The size of our brains has evolved. The human brain was once around the size of a current chimpanzee brain, and over time, it tripled in size, so we now have the largest and most complex brains of any living primate.

Yet, the brain size of our ancestors only increased in small increments for the first several million years of human evolution. Therefore, they were able to do simple tasks, like making primitive tools.

The human brain started evolving rapidly about eight hundred thousand years ago, and for the next six hundred thousand years, it continued this trend.

Most scientists believe that this was a result of the increasingly unpredictable environment, and the larger and larger brains helped people to adapt.

Moreover, one of the main differences between our brains and chimpanzee brains lies in the temporal cortex. Humans have dramatically more white matter in this brain area, meaning that we have more connections between nerve cells, and a greater ability to process information.

The evolution of the neocortex was one of the biggest changes that happened to the human brain during the time. As the human brain was rapidly growing, the cranium (aka- skulls) couldn’t keep up, so the brain became cramped, and the neocortex began folding. This is the reason why the human brain is distinctly wrinkled, unlike the brains of other animals.

The neocortex accounts for about 76 percent of the brain’s volume, and it is extremely important, as it is involved in higher functions like spatial reasoning, language, sensory perception, generation of motor commands, and conscious thought.

Numerous scientists believe that the enlargement and subsequent elaboration of this brain area is the secret behind humans’ mental abilities.

Yet, they do not know the reason behind this change and the thing that made it happen, so they placed human genes into monkeys to find out.

Scientists have identified a specific gene, unique to humans, ARHGAP11B. Its expression might have been what gave the human brains the extra oomph they needed. 

Therefore, researchers from Germany and Japan, from Germany’s Max Planck Institute of Molecular Cell Biology and Genetics in Germany and Japan’s Central Institute for Experimental Animals, introduced this gene into the fetus of a marmoset monkey to investigate whether it would make their brains grow.

And it did!

The ARHGAP11B gene caused the monkey fetus’ neocortex to enlarge!

Other studies have also shown that the same would work in mice and ferrets as well. T

Yet, this was the first time scientists have used the gene in a non-human primate.

They also introduced it in the same quantity as what is present in a typical human. 

This confirms that this gene played a key role in our evolution as human beings. 

Michael Heide, the lead author of the study, explained that once they put human genes into the monkeys, their neocortex got bigger and began to fold. He added:

“Furthermore, we could see increased numbers of basal radial glia progenitors in the outer subventricular zone and increased numbers of upper-layer neurons, the neuron type that increases in primate evolution.” 

We have to mention that such experiments on primates often raise numerous ethical questions. Plus, the introduction of human genes into monkeys adds a whole other layer to those questions.

This was why the scientists limited their research to only monkey fetuses. After one hundred days, they removed the fetuses via c-section.

The study coauthor Weilend Huttner added that it would be irresponsible and unethical to go past that point and have monkeys born with human genes:

“We confined our analyses to marmoset fetuses because we anticipated that the expression of this human-specific gene would affect the neocortex development in the marmoset.”

So, to sum it all up:

  • After putting human genes into the brains of monkeys, researchers confirmed that the ARHGAP11B gene likely caused neocortex expansion during human evolution.
  • The experiment was ended once they got the result due to ethical concerns. Therefore, it is still unclear whether this brain growth has made the monkeys smarter.

Therefore, the study has given us a better understanding of our own history. Such studies help us understand how we came to be, and why we are the way we are.

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