Chimpanzees are our closest genetic relatives in the animal kingdom, sharing 99 percent of our DNA. But inside that one percent hides perhaps the biggest difference—human-level intelligence. Dawn of the Planet of the Apes plays with the idea of closing this gap by crafting a potential Alzheimer’s cure that accidentally bestows greater intelligence on the other great apes—chimpanzees, gorillas, and orangutans—producing a highly intelligent collective led by a chimp named “Caesar.”
Uplifting a chimp is more plausible than you think. You just need to coax a chimp brain down humans’ evolutionary pathway.
At this year’s Amaz!ng Meeting–an annual meeting of scientists, researchers, and critical thinkers in Las Vegas–I spoke with Dr. Steven Novella, an academic clinical neurologist at Yale University School of Medicine to find out how genetic tweaking might lead to smarter apes. He told me that the first option is to add more raw thinking materials—neurons.
“If you’re going to make a fundamental change to ‘uplift’ chimps so that they have human-level intelligence, you first have to know that chimps have about 7 billion neurons and we have about 86 billions neurons—more than ten times as many. That’s a huge difference,” he explained. Somewhere in that differential lies Caesar.
Brain size isn’t everything. Elephants and whales have much larger brains than humans by weight, yet they aren’t considered as intelligent. Even comparing brain size to body size doesn’t quite get at animal intelligence. Elephants, for example, have a brain to body size ratio of 1/560, while mice have a ratio of 1/40, despite elephants being considered the more intelligent species. Humans have the same simple brain-to-body ratio as mice.
To get a better comparison between animals, scientists developed the encephalization quotient. While an elephant may have a bigger brain than a mouse, it doesn’t need more neurons than the mouse to draw a breath or tell its heart to beat. Therefore, an elephant can have a smaller brain relative to its body size compared to a mouse, which has a larger brain for its body size. By plotting various mammal brain and body weights on a graph and finding a mathematical curve to fit the data, scientists found an “average” mammalian brain size that varies depending on the encephalization quotient. That value, EQ, indicates if a brain is larger or smaller than the average, and correlates roughly with intelligence. As you can see below, humans have much larger brains than is predicted by the data:
How would you increase the EQ of a chimp from 2.6 to 6.6? “I don’t think there’s any way to do it without adding a lot of neurons,” says Novella.
Five to eight million years ago, the common ancestor of chimpanzees and humans split off down two paths. One led to chimps and the other, eventually, led to us. But down our path was increased intelligence. If we could steer chimp development down the more human path perhaps it would bring with it a more thoughtful ape, Novella speculates.
“The easiest way to do it would probably be to tweak the genes in the chimp so that they follow the same developmental pathway as humans. All the raw material is there, and the genetics are very, very similar. It would be very plausible to genetically engineer chimps to be more intelligent,” explained Novella. Indeed, this is basically how Caesar gains his human-like intelligence when a virus passed down from his mother alters his development!
Genetically engineering chimp embryos to develop more neurons during their growth could work, and may lead to increased intelligence, but it’s not quite what happens to all the apes in Dawn of the Planet of the Apes. Uplifting an adult chimp would be much harder, but not impossible.
“The only way I can think of, extrapolating from existing technology, would be to transplant neural stem cells that could be recruited to make meaningful connections,” Novella told me.
Here’s the basic plan to create a Caesar from an adult chimp: we insert billions of neural stem cells into his brain. We know that human brains can recruit neural stem cells that can then take up shop. Called neurogenesis, it was only recently discovered that our brain cells can and do in fact grow back. So we would douse a chimp’s brain with neural stem cells and hope they are recruited. That same technique may one day help human patients suffering from stroke or other brain diseases or damages. “It’s totally plausible to think that, for example, we could wash a person’s brain with neural stem cells who had a stroke so that when they begin recovery, they have the raw materials to help rebuild pathways,” explained Novella.
Neural stem cells sound like a magic bullet, but there’s a reason our brains and bodies aren’t awash with stem cells—too many and they can grow out of control, causing cancer. But if we perfected the technology to create and insert them, there’s no theoretical reason that a chimp brain couldn’t recruit neural stem cells and make meaningful pathways with them.
The biggest obstacle to more intelligent chimps Novella noted is that “the chimps’ brains and skulls were the same size in Dawn.” Adding billions more neurons takes up space. If you could somehow increase the number of neurons in chimp brains to really bring about the dawn of their planet, their skulls would have to change too. Either chimp skulls would have to become more bulbous like ours, or they would have to remove part of their skulls to make room.
“There’s no way around the fact that their brains would have to be bigger,” says Novella. But we could probably do it.
Kyle Hill is the Chief Science Officer of the Nerdist enterprise. Follow the continued nerdery on Twitter @Sci_Phile.