Which species has the biggest brain? Are they the smartest?

Which species has the largest brain in the animal world? And is a big brain linked to a high IQ?

In the animal world, many species show that they are very intelligent. From killer whales with terrifying hunting strategies, to cats smart enough to solve cognitive puzzles, even fish with the ability to count. So which species has the biggest brain?

The species with the largest brain

The sperm whale (Physeter macrocephalus) has the largest brain, weighing up to about 9kg - (Photo: Shutterstock)

To date, no species has surpassed the sperm whale (Physeter macrocephalus), with a brain weighing up to 9kg.

Not only that, they are also recognized for their remarkable intelligence. A 2021 study found that after several hunts, the odds of hunters hitting them with spears decreased by nearly 60%.

Perhaps sperm whales have learned to avoid hunters, or they are able to pass information on to their own species, suggesting they have communication skills and are more intelligent than originally thought.

However, when "classifying" the brain, we should also consider the structure of the brain itself. The cerebellum is a structure responsible for movement, balance, tracking, and some memories.

In sperm whales, the cerebellum accounts for about 7% of the total brain mass, while in killer whales, this number is double, about 14%. For humans, the cerebellum accounts for about 10% of the average human brain mass, weighing about 1.4kg.

An animal's total body size also needs to be considered when evaluating the largest brain. If considered according to this criterion, the "champion" is the Brachymyrmex ant: the brain accounts for 12% of their total body mass of 0.049 milligrams, according to a 2009 study.

This is consistent with the so-called Haller's rule: the larger the animal in overall size, the smaller the brain-to-body ratio. "Because brain size is proportional to body size, the smallest animals have the largest relative brain-to-body ratio ," Wulfila Gronenberg, a professor of neurobiology at the University of Arizona, told Live Science .

Small brain but smart

Crows are as intelligent as great apes, although they have much smaller brains - (Photo: Pinterest)

A dataset of 1,400 mammals (including some fossil species) compared their brain and body sizes and showed some surprising results. Accordingly, the California seal, although famous for the spectacular tricks it can perform, has a small brain compared to its body mass.

In contrast, humans and dolphins have smaller bodies but larger brains. In chimpanzees and orangutans, although they are similar in size to humans, their brains are only about one-third the size.

Then there is the interesting phenomenon of domestication syndrome, where domesticated species have smaller brain sizes than their wild counterparts. For example, the fighting bull had a brain roughly the same size as that of the extinct wild bison, the aurochs (Bos primigenius). Beef and dairy cows that come into frequent contact with humans have the smallest brains.

Among land animals, elephants have the largest brains and demonstrate high levels of social, emotional, and memory intelligence.

Among land animals, elephants have the largest brains and demonstrate high levels of social, emotional and memory intelligence - (Photo: worldwildlife.org).

Let's not forget about birds, with crows being famous for their intelligence. A study by researchers at Lund University found that crows are as intelligent as chimpanzees despite their different brain sizes.

"Brain size isn't everything. We discovered that corvids are as intelligent as great apes, despite having much smaller brains ," said study author Can Kabadayi.