Where are whales’ brains located?

The sperm whale lives up to its scientific name, Physeter macrocephalus, which means “big head.” Measuring up to 18 metres long and weighing up to 50 tonnes, the anatomy of this giant easily sets it apart from other species. It is also the largest of the toothed cetaceans, in addition to holding the title for the most massive brain in the animal kingdom, weighing up to 9 kg! However, it is not found in the space above the jaw, but rather behind the eyes, where its skull hides. As can be seen in the illustration of Ali Nabavizadeh, the top of the jaw is composed of fatty and muscular tissues. The melon, the spermaceti (from which the species derives its name), and muscles are found here. These organs are used for emitting sounds for echolocation.

Since baleen whales lack a melon, their heads have a more slender and more elongated profile. Compared to toothed whales, baleen whales have smaller brains relative to their body size. However, their skull and brain are still located behind their eyes, just like in belugas and sperm whales!

In and of itself, brain size is not directly proportional to cognitive ability. A larger brain does not necessarily translate into superior intelligence. In research, scientists instead use the encephalization quotient (EQ), which represents the ratio between the actual size of the brain and how large it might be expected to be given the size of the animal overall. In humans, the EQ is between 7.4 and 7.8, meaning that the human brain is about seven times larger than one would expect given our body size. Incidentally, humans have the highest EQ of any animal, followed by odontocetes. A few species of toothed whales, including dolphins, also have fairly high EQs of between 4 and 5, which is higher than those of primates. On the other hand, all species of baleen whales have a ratio of less than 1. Lastly, studies reveal that in all cetaceans, brain size changes as they evolve. These changes indicate that these species have adapted to their environment that requires them to process large volumes of information, as well as to the demands of pod life such as communication, cooperation and competition.