Mental illness exists for a reason (part 1)

Damn you, Mother Nature!

It’s complicated.

Deep in the Democratic Republic of the Congo, near the South Congo River, lives the rarest species of great ape in the world – Bonobo chimpanzees. Why are the great apes important? They are the animals most closely related to humans on the planet! And they’re also the next most intelligent animals on the planet. These animals exhibit complex social behaviours and relationships, and members include chimpanzees, bonobos, orangutans, and gorillas.

Bonobos are particularly interesting because they only live in one place in all of the world – the South Congo River. This is in contrast to traditional Chimpanzees, who have ranges all across the African continent. This has resulted in Bonobos being the last discovered great ape and have therefore been the least studied! Until recently, that is.

Chimpanzees are notoriously aggressive. Jane Goodall infamously documented a brutal chimpanzee civil war when she lived among the apes in 1974-1978. Chimpanzees have a complex social structure, with rank and sexual capital determined by violence. Bonobos, on the other hand, are like your cool uncle. They do not appear to compete for rank, males are often subordinate to the females, sex is often homosexual and not for the purposes of procreation, they are considerably more sexually active than Chimpanzees, and importantly, are non-violent!

Scientists have been trying to understand the basis for the differences in behaviour for some time, in hopes that this can lead to a better understanding of the operation of the human mind. Genetic studies have begun to uncover key differences in the genomes of both apes. It turns out Bonobos are the second most related ape to us, after the chimpanzee, and Bonobos appeared to diverge genetically from Chimpanzees between 2 and 2.5 million years ago.

So what happened?

Geological studies show that 2.5 million years ago, in the Zaire river, there was a large drought, which pushed the previous chimpanzee-bonobo ancestor out of that area. The group diverged, with the river being a dividing line. Those apes that went South of the river, found food plentiful. They were able to continue the fibre, plant-based diet the apes always had eaten. These apes are what we now call Bonobos. This was not the case for the apes which moved North. These apes had to compete with African Gorillas for scarce food resources, and due to competition and food scarcity, had to shift their diet to an omnivorous one, and include meat. These apes have evolved into Chimpanzees. You can read more about that here!

So what explains the stark difference in their behaviour? If you recall, I mentioned earlier that Bonobos and Chimps are our two closest relatives; both Bonobos and Chimpanzees are more related to each other than we are related to them. That provides a pretty interesting opportunity. Because Bonobos and Chimps are so closely related, it should be relatively easy to find differences in their genome, which provides an opportunity to find the gene, if there is one, responsible for this change in behaviour.

I won’t get into the technical stuff here, but it turns out that is the case. This study identified a key mutation in a gene (vasopressin 1a receptor gene) which occurred in Chimpazees and has been associated with lower sociability and increased anxiety. It makes sense why these traits are helpful when you are forced into competition with one another, and Gorillas, and have to hunt meat. Bonobos on the other hand carry the non-deleted form of the gene, which has been associated with increased openness to each other. You can read more in the previous link (it’s technically heavy) but the researchers argue pretty convincingly that this is the genetic basis for the differences in personality!

It turns out humans, and… prarie voles? also contain the gene for vasopressin 1a receptor. In part 2, we can use our understanding of this gene in humans to extrapolate why mental illness may exist!

 

Editor’s note: I do not want to diminish the role of, “nurture,” in the nature vs nurture argument. By no means in personality 100% genetic (most studies show it’s around 50%)! This blog simply looks at the genetic side of things.

I would like to credit Dr. Albert Wong at the Centre for Addiction and Mental Health for inspiring most of the content of this blog post.

Dr. Travis Barron is a resident physician in Toronto, Canada.