It is hard to connect "smarts" intelligence with brain size differences in animals. In some cases it is possible to judge intelligence and brain size, like if we were to compare a frog brain and a cat brain. However, when you compare the brains of the same animal species you run into problems. So it is difficult to connect brain size and intelligence when you compare one cat with another cat or a human to another human.
Something for you to think about: Elephants have a much larger brain than humans. Are elephants smarter than us?
Once you answer that question, try answering this one. Is an elephant smarter than a mouse?
These are the same questions that scientists are asking. What they are learning is brain size alone is not a good indicator of intelligence. Instead, they are looking at more than brain size. They are looking at how the brain is organized and the size of different parts of the brain, like those that control speech, and memory. It is most likely a combination of these things that will provide the best answer to intelligence.
Let me leave you with one more piece of information. While humans do not have the largest brains of all mammals, they do have the largest brain in relation to their body size. Do you think this might have something to do with the difference in intelligence between mammals? Why?
To learn more about the brain, try these links.
PET image in the public domain by author, Jens Maus
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Dr. Biology. (2016, July 19). Does brain size relate to intelligence?. ASU - Ask A Biologist. Retrieved September 22, 2020 from https://askabiologist.asu.edu/fr/questions/does-brain-size-relate-intelligence
Dr. Biology. "Does brain size relate to intelligence?". ASU - Ask A Biologist. 19 July, 2016. https://askabiologist.asu.edu/fr/questions/does-brain-size-relate-intelligence
Dr. Biology. "Does brain size relate to intelligence?". ASU - Ask A Biologist. 19 Jul 2016. ASU - Ask A Biologist, Web. 22 Sep 2020. https://askabiologist.asu.edu/fr/questions/does-brain-size-relate-intelligence