(Author: Eric Malikyte)

The question of how modern humans diverged from our chimpanzee cousins has been a puzzle long on the minds of scientists.

It’s thought that something happened to us millions of years ago which led to the development of larger brains as well as all the benefits that came with a larger neocortex.

Amazingly, in 2016, the research group of Wieland Huttner discovered some surprising things about one of our genes.

According to this study, ARHGAP11B contains 47 amino acids that are specific to humans. These amino acids are not present in ARHGAP11A (which is found in Chimpanzees), suggesting that ARHGAP11B is responsible for the development of larger brains in modern humans and our extinct cousins, the Neandertals.

The results of this 2016 study have led scientists at the Max Planck Institute to perform a controversial gene-edit on a Marmoset embryo, resulting in a fetus with a much larger neocortex than it ordinarily should have.

And we’re going to talk all about it.

Bigger Monkey Brains

Scientists at the Max Planck Institute of Molecular Cell Biology and Genetics think they’ve cracked the moment in our evolutionary timeline where our ape descendants became human.

The human brain’s size is largely what sets it apart from other primates.

But would you believe that this difference is primarily accounted for by the presence of one gene?  

Incredibly, when the scientists at the Max Planck Institute in conjunction with the Central Institute for Experimental Animals in Japan introduced the gene ARHGAP11B into a developing monkey fetus, they found that the monkey’s brain not only increased in size, but also began to resemble a human brain..

On the left is a normal Marmoset brain, on the right is the more humanlike features that the Marmoset fetus in the experiment developed after having the ARHGAP11B gene substituted for ARHGAP11A. Heide et al./MPI-CBG

In the 2016 study performed by the research group of Wieland Huttner, they observed that a single C-to-G base substitution resulting from the introduction of ARHGAP11B caused the loss of 55 nucleotides from the gene’s messenger RNA. This also caused a shift in the reading frame resulting in the human-specific, functionally critical 47 amino acid sequence.

Now, this experiment is definitely going to ruffle some feathers, much like those dinosaur chicken embryos from 2016 (pun, definitely intended), but the scientists involved in the experiment all claim to be operating under strict ethical guidelines.

Which is good, because the titles for many of the articles this episode is based on warn of the impending war between humanity and ape kind, fueling ethical debates in the comments sections of many of these journalistic websites.

But if you, like some of these people, are worried about the Planet of the Apes franchise of movies becoming our new reality, maybe go outside and breathe some fresh air, you’ve been in quarantine too long.

Though, at the time of recording this video, it is still 2020, so who knows, maybe future me will meet his new Marmoset masters before the start of 2021? If only there was some way to communicate with future me?

Okay, all joking aside, no monkeys are not suddenly going to rise up and overtake humanity’s place in the Darwinian pecking order.

The teams of scientists behind this study haven’t even allowed the fetus to come to full term due to ethical concerns (which, again, we’ll get into later).

So, what exactly happened to this monkey’s brain?

Well, you can see in this image some of the visual differences, but there’s more to this brain than meets the eye.

For one, the size of the monkey’s neocortex has increased. Two, the monkey’s brain now exhibits similar folding to a human brain. Three, the relevant pro-generative cell type, that produce neurons, has also increased. And four, upper layer neurons have increased, which scientists theorize happens in evolution.

Co-author of the study, Michael Heide said this in regards to the study, “This shows, basically, that the gene — and its expression in humans — is sufficient to expand and to fold the primate, or the monkey, brain.”

This is an incredible development. The neocortex makes up about 75% of our brain and is responsible for many of the things that set us apart from our primate brethren. Without your neocortex, you wouldn’t be able to use complex reasoning or complex language, (not that most humans take advantage of this…ahem…evolutionary upgrade—I’m looking at you Zack Snyder, your movies are terrible!).

Human Evolutionary Timeline

If our evolutionary timeline were compared to a set of train tracks, then effectively our hominid ancestors would have switched tracks at a certain point in our distant past, and the other track would lead to where our chimpanzee cousins are now.

Our distant ancestors’ brains underwent a rapid change, nearly tripling in size over the course of 3 million years! Now, this may seem like a lot of time, but this actually resulted in the brain becoming quite cramped in our slowly evolving cranium, resulting in the folding into wrinkles we see in the neocortex.

Scientists think this was all because of the effects of ARHGAP11B and this would also be true for our now-extinct close cousins the Neanderthals, (which, as another side note, 2% of all people who have Eurasian descent have traces of) and Denisovans.

So, remember this study when your crazy uncle starts rattling off about how he’s not a monkey (because we all definitely are and this study and the entire fossil record proves it).

Studies done on mice and ferrets have also shown that ARHGAP11B caused an enlargement of the neocortex in those species, which was the first concrete evidence that the gene played a major role in our evolution (it also makes me think rat-people and ferret-people are suddenly possible).

It’s thought that ARHGAP11B showed up in our ancestors’ DNA 5 million years ago and was accidentally introduced when copying the everyday gene ARHGAP11A. With this happy little evolutionary mistake, this single substitution of one little nucleotide base (nucleotides are the molecules that are sponsible for encoding DNA) resulted in the loss of 55 nucleotides from ARHGAP11B.

But this change would have been gradual, only completing about 1.5 to 500,000 years ago.

This mistake caused our ancestors’ neuron-producing cells to replicate more of themselves over longer periods of time. The end result, as you’ve probably guessed, was a larger neocortex.

Now, according to evolutionary scientists, these point mutations are not rare, but the advantages that ARHGAP11B offer most likely greatly affected our evolution.

Don’t you think it’s incredible that the change of one little piece of our DNA could result in us becoming…well, us?

I do.  

But this study definitely raises some ethical questions about gene editing, which is a mess we’re about to dive right into against our better judgment and because I’ve got nothing better to do apparently.

Ethical Questions

Now, the following information may upset some viewers, so stop now if you’re sensitive to the subject of animal testing (but not before liking and subscribing for more content, hah, shameless plug, nailed it.)

The fetus samples for this study came from Japan, and the Max Planck Institute brought them over to Germany to set up the experiment. The fetus grew for 100 days before the scientists involved with the experiment performed a cesarian section operation on the mother.

It’s the opinion of those scientists that to let this gene-edited Marmoset be born into the world would be extremely irresponsible because we simply don’t know what sort of behavioral changes would result in the developing human-brained monkey.

This is similar to how scientists decided not to allow the embryos of their gene-edited chickens (which had developed dinosaur-like snouts as a result of their messing about with their DNA) to hatch.

Calmly contemplating how to take over the Earth, Credit: Mike R derivative work of Fama Clamosa, CC BY-SA 3.0

(But as a side note, the scientist behind that study totally thinks those chicken dinos would be fine if allowed to live a full life and now I want a dino chicken as a pet)

But what do you think? Do you think that the scientists should have allowed the human-monkey hybrid to be born, despite the health issues it may have potentially developed? Or do you think the scientists made the right call here?