People of cats and dogs have long argued about which species has the best brains.
The Cat Team points out the self-sufficiency of felines as a sign of intelligence. Animals can hunt, which is not so good for wildlife, but it shows the cunning predator that still lurks inside the kittens given away. Cats also clean themselves, make their needs in tidy litter boxes, or even toilets, and are generally better at controlling the food portions than their canine companions.
Team Dog cites the ability of canines to learn complex tasks, especially those that benefit humans. Dogs guide the blind, raise cattle, sniff explosives and help find survivors buried under the rubble of the earthquake. They also have good memories and an impressive ability to understand human language.
But it turns out that all this list of summaries may be unnecessary. According to a new study published in Frontiers in Neuroanatomy, the best way to measure cognitive ability is to count the neurons of each animal.
Neurons are cells that communicate through the electrical charge and populate the brain and central nervous system. They are the units that process the information. Although measuring intelligence is an incredibly difficult task, Suzana Herculano-Houzel, a neuroscientist at Vanderbilt University, and her colleagues believe that her method of quantifying neurons in an animal's brain, especially in the cerebral cortex, is the most important tool precise to judge your ability to complex thinking.
So, what animal comes out ahead in the Census of the Great Neuron? Get ready, Team Cat.
"Dogs have about twice as many neurons as cats," said Herculano-Houzel, who wrote a book on brains called "The Human Advantage."
But wait: the average dog is bigger than the average cat. Is not it true that dogs would have bigger brains and, therefore, more neurons? This is where things get interesting.
The study found that the total mbad of one's gray matter is not important. In addition to the dog and the cat, the team examined the brains of a domestic ferret, a striped mongoose, a raccoon, a striped hyena, an African lion and a brown bear. While the brain of the brown bear was three times larger than that of the dog, the dog had more neurons. In fact, the brown bear's neuron count was similar to that of the cat, an animal whose brain is approximately 10 times smaller.
To put some numbers in play here, a cat has 250 million neurons in the cerebral cortex for a 530 million dog. Both species are eclipsed by the average human being, who registers 16 billion cortical neurons.
But one of the most surprising ideas in the research has nothing to do with cats, dogs or people. These are raccoons, those "garbage pandas" that have long been discarded as parasites or vectors of the rabies virus. Within the brain the size of a raccoon cat lurks an amount similar to a neuron dog. So many, in fact, that if you only looked at the brain count and the size of the brain, you could confuse the raccoon with a small primate.
"And that's saying a lot," said Herculano-Houzel. "Because something we discovered earlier is that there is a big difference between the number of neurons found in a primate or a non-primate brain of the same size."
Jessica Perry Hekman, a veterinary geneticist at MIT and Harvard's Broad Institute, said there are a number of reasons to be cautious when interpreting the results of the study. On the one hand, he said, the link between the number of neurons and intelligence is anything but proven.
"What does not mean it's wrong," Hekman said, "but it's definitely something that you're starting with and collecting information on."
The study also had a small sample size. With the exception of dogs, which contributed two brains to the study, each of the other species was represented by a single brain. (Good brains are hard to come by, Hekman acknowledged.)
The comparison of the study of domesticated, wild and zoo animals could also have a major influence on the results, Hekman said. Researchers have discovered that the experience affects brain development, especially in the first years of life: rats raised in pens with lots of enrichment, such as toys or complicated territory to explore, develop more synapses or connections between neurons than rats raised in cages sterile Therefore, it is possible that the life history of the hyena or the mongoose badyzed played a role in the anatomy of your brain. Hekman said he believes that the number of synapses of an animal, rather than neurons, could be a more accurate measure of its intelligence.
But the biggest problem, and the one that both Hekman and Herculano-Houzel are trying to solve, is that intelligence is a hard nut to crack. In fact, it can be several different nuts. Each species has different abilities and challenges.
"I'm not even really sure we should call intelligence a trait," Hekman said. "It's a lot of different things."
Even if this document is not the definitive guide for animal intelligence, it reveals some interesting facts. For example, why do larger carnivores like the lion and the bear have fewer neurons than we would expect for animals of their size?
According to Herculano-Houzel, it is not that the biggest predators can get away with being stupid. At the beginning of the study, she and her team badumed that the predators would have significantly more neurons than the prey they hunted, because they thought that hunting is a more challenging way of life. Most lion hunts end in failure, for example, and every day is a battle to consume enough calories to reach the next kill. An ñu, on the other hand, can be filled with plants in their free time and form large herds that minimize their chances of becoming lions.
Instead, the team discovered that lions and hyenas had similar ranges of neurons as relative size prey animals, such as blesbok and kudu.
But would not it make sense for evolution to produce increasingly intelligent predators, whose cleverness would result in catching more prey? Well, yes, but even evolution has to work with a budget.
"Neurons, especially neurons in the cerebral cortex, are extremely expensive in energy terms," said Herculano-Houzel. "There is a point where you can not afford a huge body as much as a lot of neurons."
The science of comparing animals is still evolving, and Herculano-Houzel said it would be great to incorporate neural information in a manner consistent with behavioral studies. It would also be valuable to count the neurons of many brains of the same species to obtain a better range, as Hekman suggested. The count of dog neurons came from just two animals, a mixed breed and a golden retriever. Who knows what kind of differences can be found among chihuahuas, mastiffs and corgis?