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Thus, large whales have very small brains compared to their weight, and small rodents like mice have a relatively large brain, giving a brain-to-body mass ratio similar to humans. [4] One explanation could be that as an animal's brain gets larger, the size of the neural cells remains the same, and more nerve cells will cause the brain to ...
Proxies for animal intelligence have varied over the centuries. One early suggestion was brain size (or weight, which provides the same ordering.) A second proposal was brain-to-body-mass ratio, and a third was encephalization quotient, sometimes referred to as EQ.
An elephant's brain weighs just over 5 kg (11 lb), a bottlenose dolphin's 1.5 to 1.7 kg (3.3 to 3.7 lb), whereas a human brain is around 1.3 to 1.5 kg (2.9 to 3.3 lb). Brain size tends to vary according to body size. The relationship is not proportional, though: the brain-to-body mass ratio varies. The largest ratio found is in the shrew. [57]
The relationship is not linear, however. Generally, small mammals have relatively larger brains than big ones. Mice have a direct brain/body size ratio similar to humans (1/40), while elephants have a comparatively small brain/body size (1/560), despite being quite intelligent animals. [18] Treeshrews have a brain/body mass ratio of (1/10). [19]
The brain to body mass ratio (not the encephalization quotient) in some members of the odontocete superfamily Delphinoidea (dolphins, porpoises, belugas, and narwhals) is greater than modern humans, and greater than all other mammals (there is debate whether that of the treeshrew might be second in place of humans).
Shrews have the largest brain-to-body mass ratio of any animal, with brains that are 10% of body weight. Humans however have the largest encephalization quotient of any animal. [20] Dogs have the largest heart-to-body mass ratio. [21] The jerboa has the largest ear as a proportion of its body size. [22]
Comparing brain size at birth to the size of a fully developed adult's brain is one way to estimate how much an animal relies on learning as opposed to instinct. The majority of mammals are born with a brain close to 90% of the adult weight, [ 23 ] while humans are born with 28%, [ 23 ] bottlenose dolphins with 42.5%, [ 24 ] chimpanzees with 54 ...
The range with which the adult brain in all animals regardless of body size consumes energy as a percentage of the body's energy is roughly 2% to 8%. [3] The only exceptions of animal brains using more than 10% (in terms of O 2 intake) are a few primates (11–13%) and humans. [3]