Having a bigger brain does not guarantee more cognitive power. Although many believe humans are the smartest species on the planet, our brains — which weigh roughly three pounds — are dwarfed by other animals. For instance, the elephant brain weighs about nine pounds; the whale brain can weigh up to 20 pounds.
It’s not all that surprising that the bigger an animal's body, the bigger its brain might be. However, when scientists rank mammals by their brain size relative to their body size, it's the tree shrew, and not humans, that come out on top. The brain of the tree shrew accounts for 10 percent of its body mass, while the human brain accounts for roughly two percent of body mass.
What then makes the human brain special? Most scientists agree that we owe our unique capabilities to the complexity of the cerebral cortex, the outer layer of the brain that is responsible for awareness, planning, and reasoning. With 16 billion neurons, the human cerebral cortex has the most neurons of any in the animal kingdom, and each neuron can form tens of thousands of synapses with other neurons. These neurons and their connections are supported by specialized cells called glia, which are also believed to play an important role in human cognition.
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