A person’s interest in dinosaurs often ends with childhood, but Anton Reiner, PhD, has been able to carry his fascination with the prehistoric animals into his career at UTHSC.
After the topic of dinosaur intelligence recently returned to the forefront, Dr. Reiner, an emeritus professor in the UTHSC College of Medicine’s Department of Anatomy and Neurobiology, chimed in through an article published in the Journal of Comparative Neurology.
“I wanted to address the science fiction issue of whether or not dinosaurs, given they had a pretty solid, substantial brain, could have evolved to a human level of intelligence,” he said.
The article serves as a response to a study by Suzana Herculano-Houzel, PhD, of Vanderbilt Brain Institute, in which she estimated the likely number of neurons in a dinosaur brain. She concluded therapod dinosaurs, like the Tyrannosaurus Rex, could have had roughly the same number of neurons as a baboon and could have evolved to have human-like numbers of neurons if they had not gone extinct some 65 million years ago. According to Dr. Reiner, while that may be true, intelligence is not determined only by how many neurons a creature has.
“It’s not just the number of neurons, it’s how they’re arrayed and connected,” he said. “They have to be arrayed in such a way that they are connected efficiently, and they’re not going to be connected efficiently in a dinosaur, bird-type design.”
Dr. Reiner has spent decades studying brain evolution, along with brain and eye diseases and how to treat them therapeutically. “Brain evolution has always been a major theme in my research,” he said. “I’ve been interested in evolution in general since I was a child, and if you’re interested in evolution as a child, you’ll be interested in dinosaurs.”
Knowledge of how dinosaurs’ brains worked became much clearer with the recent thinking that dinosaurs are the origin of birds. According to Dr. Reiner, it is safe to assume dinosaur brains were similar to those of birds in size, shape, and functioning, and were different from human brains in some crucial ways.
In the brains of humans and other mammals, neurons devoted to thought and planning—described by Dr. Reiner as “the seat of intelligence”—form a sheet called the neocortex that is about one-fifth of an inch thick in humans. In this sheet, the neurons that form the basic processing unit are arrayed closely to one another in a column from superficial to deep. Because the neurons of the processing unit are packed closely together in the cerebral cortex—the wrinkly outer layer that covers the brain—they can efficiently process information from intake to analysis to action.
“Birds are not stupid by any means, and parrots are pretty remarkable in what they can do, but my argument is they could not expand their brain to a human level of intelligence because of their inherent inefficiency.”
Dr. Anton Reiner
While neurons in avian brains are densely packed and roughly as numerous as those of some primates, birds’ thinking and planning neurons are organized into separate clusters in the “thinking” part of the brain, rather than closely spaced in the columns that make up the neocortical sheet. Dr. Reiner said the greater distance between the neurons in the clusters making up the thinking part of a bird’s brain means it could never operate as efficiently as a human’s, and increasing the number of clusters would only drive them farther apart, making them even less efficient. By contrast, in human evolution, the neocortex expanded by adding more processing units next to one another, with the neurons within a column always remaining close to one another.
“The fundamental argument is that the neocortex is more efficiently wired for information analysis because the neurons that do the critical analysis are close together. In the avian design, and what would have been the dinosaur design, they’re not close together to begin with, and as you add more processing elements, they’re pushed farther and farther apart. That makes that design less efficient,” Dr. Reiner said. “It works pretty well for many birds. Birds are not stupid by any means, and parrots are pretty remarkable in what they can do, but my argument is they could not expand their brain to a human level of intelligence because of their inherent inefficiency.”
In his paper, which was referenced in an article in Scientific American, Dr. Reiner also refutes renowned paleontologist Dale Russell’s belief that if an animal’s brain were big enough, and if the animal were bipedal with dexterous hands and frontal vision, the animal would naturally become as smart as a human. While that is what happened with primates, Dr. Reiner said it is not necessarily the case with dinosaurs because those factors would not have changed how the dinosaur’s brain is laid out.
With the conversation about relating intelligence to brain organization now opened, Dr. Reiner said he wants his article to serve as a challenge for scientists. He believes there is more to be discovered about the structure of the avian-paleo brain and how birds have adapted to overcome limitations caused by the layout of their neurons. He said it is yet to be determined for certain whether the way the human brain is organized really is superior as it is currently thought to be.