02 December 2005

Human Brain Hubris

Image: Sagittal sections of a human brain and a dolphin brain. Human brains are walnut-shaped but dolphin brains are nearly spherical -- so in terms of volume, side views (or sagittal sections) are misleading. If you've seen a dolphin brain in a museum you may have noticed that the neocortex appears to be even more convoluted than a human brain. Dolphin researchers have found that one hemisphere can sleep while the other is awake. The brain of a bottle-nosed dolphin is heavier than a human brain, but neuroscientists say that the important factor is the ratio of brain weight to body weight. Dolphins have a larger volume of body fat for insulation than humans. There are some small rodent species which have an even higher ratio than humans. The tree shrew has the largest brain to body ratio of all mammals (see: Is Bigger Always Better?).

Both whales and dolphins can communicate with each other through intricate patterns of sound. So far, the nature of their communication system is not fully understood by PhD-grade hominids.

Whale and elephant brains are considerably larger than human brains. Eric Chudler, an associate professor at the University of Washington, has compiled a page of Brain Facts and Figures, which includes a comparison of brain weights for a variety of species. Reported average brain weights differ from one academic source to another, but Eric Chudler has listed the textbooks he used to gather the figures. The following table shows a selection from the data:
SpeciesAverage Brain Weight (grams)
Sperm whale *7,800
Bottle-nosed dolphin 1,500-1,600
Adult human1,300-1,400
* Blue whales are the largest mammal, but sperm whales have the largest brain.
Neuroscientist Lori Marino (Emory University in Atlanta, Georgia, USA) and her colleagues used computed tomography to estimate the brain and body size of 36 fossil whale species and compared them to those of modern toothed whales. Dolphins are a type of toothed whale. She reports that there have been dolphins swimming in the oceans with huge brains for more than 15 million years. And although whales haven't shared a common ancestor with primates for 94 million years, she says:
"Nevertheless, during evolution, whales have converged upon very similar capacities and behaviours to those of primates, including a highly developed social structure, which tells us that there is more than one way to evolve a complex intelligence."


On Monday, 19 December, 2005, Anonymous Anonymous said...

If scientists can't understand how whales communicate, what is the point of spending XXX millions of dollars on equipment to search for messages from intelligent life in other parts of the universe? Whales are mammals - as we are. Extraterrestials could be BILLIONS of years in advance of humans. Now that's what I call hubris!

On Thursday, 02 March, 2006, Anonymous Anonymous said...

The Onion has a nice parody about signals received from Extraterrestrials.


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