Yesterday, we were putting down media reports on a study that purports that dolphins are not intelligent despite behavioral studies and big brains. Today, NYTimes has a much better article arguing that manatees, despite their small brains, are more intelligent than previously thought.
It is a longish article but well worth reading. The idea is that manatees don’t have too small brains, but overlarge bodies, and, since they are herbivores with no prey or predators, they do not need to reserve vast portions of their brains for tackling hunting and defense.
Brain size has been linked by some biologists with the elaborateness of the survival strategies an animal must develop to find food and avoid predators. Manatees have the lowest brain-to-body ratio of any mammal. But, as Dr. Reep noted, they are aquatic herbivores, subsisting on sea grass and other vegetation, with no need to catch prey. And with the exception of powerboats piloted by speed-happy Floridians, which kill about 80 manatees a year and maim dozens more, they have no predators:
“Manatees don’t eat anybody, and they’re not eaten by anybody,” Dr. Reep said.
But he also suspects that rather than the manatee’s brain being unusually small for its body, the situation may be the other way around: that its body, for sound evolutionary reasons, has grown unusually large in proportion to its brain.
A large body makes it easier to keep warm in the water — essential for a mammal, like the manatee, with a glacially slow metabolism. It also provides room for the large digestive system necessary to process giant quantities of low-protein, low-calorie food.
Manatees have a relatively thick cerebrum, with multiple layers that may, Dr. Reep suspects, indicate complexity despite a lack of folding.
In any case, he said, brain convolution “doesn’t seem to be correlated with the capacity to do things.”
More to the point, intelligence — in animals or in humans — is hard to define, much less compare between species, Dr. Reep said. Is the intelligence of a gifted concert pianist the same as that of a math whiz? Is a lion’s cunning the same as the cleverness of a Norwegian rat?
The manatee is good at what it needs to be good at.
The rest of the article focuses on manatees’ sensory capabilities, especially the somatosensory system. Manatees have vibrissae (long hairs, usually seen only around the faces of animals like cats and dogs), which are thought to be involved in the sense of touch, spread all over the body. The article incorrectly states that the only other mammal with vibrissae all over the body is rock hyrax. There is another one, though, which is much better studied in this regard – the naked mole-rat.
Also, the article states that manatee is unique among mammals in the ability to hear infrasound. That is also wrong – a lot of mammals, especially large mammals are capable of hearing infrasound. The best studied are elephants and whales, but it was also described in giraffes (von Muggenthaler, E., Baes, C., Hill, D., Fulk, R., Lee, A., (1999) Infrasound and low frequency vocalizations from the giraffe; Helmholtz resonance in biology, invited to the Sept. 2001 AZA conference, presented at the regional Acoust. Soc. Am. conference 2001.) and rhinos, while the infrasound vocalizations were made from okapis, tigers, horses and cows, as well as in some non-mammalian vertebrates, including crocodiles and perhaps some birds.
So, in light of our discussion yesterday, what do you think?