Dolphins are stupid but happy, according to a South African researcher, and their brains are only as large as they are to keep them warm in the sea.
Paul Manger from Johannesburg's University of the Witwatersrand, argues that dolphins' large brains have fooled us into thinking they are smart. In reality, he says, the marine mammals couldn't outwit a rat, and don't have the sense of a goldfish.
Not counting humans, dolphins have the largest brain to body size ratio of any other creature on the planet. However, what Manger says is that since most of that brain mass is made up of so-called glial cells, rather than neurons, the size is irrelevant. He argues that the glia merely act as insulating material.
As Poirot would say, it is all about the leetel grey cells.
Despite this lack of "thinking" brain, dolphins are probably as happy as they look. Manger says they produce a huge amount of the neurotransmitter serotonin. This plays an important role in regulating mood, sleep and appetite. It is also often referred to as the happy drug.
Of course, any suggestion that dolphins aren't secretly playing chess in their spare time was bound to attract criticism.
Vancouver Aquarium's cetacean research programme head Dr Lance Barrett-Lennard says Manger's argument could be just as misleading as simply relying on brain/body ratios to inform us about the intelligence of animals.
He argues that dolphins' behaviour clearly indicates that they are highly intelligent.
"A dolphin could have a brain the size of a walnut and it wouldn't affect the observations they live very complex and social lives," he told The Globe and Mail. "They keep account of who their friends are with very complicated hierarchies and allegiances. The other thing is they have spatial maps. They know exactly where to go when they need to look for certain food."
Manger counters that dolphin behaviour supports his assertion that they are in the "two short planks" category.
"You put an animal in a box, even a lab rat or gerbil, and the first thing it wants to do is climb out of it. If you don't put a lid on top of the bowl a goldfish it will eventually jump out to enlarge the environment it is living in," he said.
"But a dolphin will never do that. In the marine parks, the dividers to keep the dolphins apart are only a foot or two above the water between the different pools."
He argues that if dolphins were really that bright, they would jump over tuna nets instead of getting caught in them.
Manger's research has been peer-reviewed and is published in Biological Reviews of the Cambridge Philosophical Society. ®