Brains of mammals got bigger over the past 150 million years

The relationship between body size and brain is one of the main criteria by which scientists determine how intelligent an animal is. A new study by 22 experts from Max Planck and Stony Brook University in New York is trying to answer a complex question: how has this ratio changed in mammals over the past 150 million years? The researchers compared the brain mass of a total of 1,400 species. Fossils have been used to study 107 of them, as the species in question have long since disappeared. Among them are some of the most ancient whales and monkeys known to science.

According to the results of the study, the relationship between body size and brain has not changed evenly over the course of evolutionary development. For millions of years, elephants, for example, have increased both the size of their bodies and their brains. At the same time, dolphins have shrunk, but their brains have become larger. A similar trend is observed in apes. Scientists believe that the models they have prepared show how wrong it is to make a connection between the intelligence of a species and the ratio between the size of its body and its brain.

“The facts we have show that this ratio is relatively insignificant,” said Jeroen Smaers, an evolutionary biologist at Stony Brook University and one of the study’s authors. “Let’s focus on the California sea lion. These animals have small brains compared to their bodies. However, they are known for their remarkable intelligence,” said Smaers. it is associated with predators that posed a threat to it and can be defined as a protective reaction that has no negative effect on his intelligence. , adds Smaers.

“With the results of our study, we were able to reverse the long-held notion that the relative size of the brain to the body can be equated with the level of intelligence,” said Kamran Safi of Max Planck, who is also one of the study’s authors. “The truth is that sometimes the brain can be the end result of a gradual reduction in body size caused by factors such as a new habitat or mode of movement – in other words, it has nothing to do with intelligence. Using the relative size of the brain as “An indication of a species’ cognitive abilities must take a back seat. Much more important is evolutionary history, the nuances of the way the brain and body have changed over time,” Safi said.

The new study also revealed something curious: the most significant changes in the brain size of a number of mammals occurred after two catastrophic events. One of them is the mass extinction of species about 66 million years ago (when the dinosaurs disappeared), and the other – the climate transition that occurred before 23 – 33 million years. Scientists have found that after the mass extinction at the end of the Cretaceous period a dramatic change in the ratio of brain to body size in a number of mammals that began to fill niches left empty after the extinction of the dinosaurs.

Approximately 30 million years later, at the end of the Paleogene, the climate began to cool, which also led to drastic evolutionary changes. Then the bodies and brains of many animals, including seals, bears, whales, and primates, increased in size. “The results of the study definitely surprised us. Much of the variation in the relative brain size of many modern mammals, such as dolphins, elephants, and apes, can be largely explained by the changes that occurred in their ancestors during these two catastrophic events, “said Smaers.

The study’s authors add that analyzing the evolution of intelligence requires a detailed study of certain neuroanatomical features, such as those parts of the brain associated with complex cognitive processes. “Undoubtedly, the relationship between the size of the brain and the body is in some respects directly related to intelligence. However, the conclusions we have reached unequivocally show that to a much greater extent it is the result of the adaptation of some species to the great pressure that the environment has put on them in the past, “added Smaers.

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