A BIG brain is a sign of a healthy immune system, at least as far as male birds are concerned.
Anders M酶ller at Pierre and Marie Curie University in Paris, France, and colleagues examined data from 127 bird species. They found that in species with larger brains for their body size, such as yellowhammers and barn swallows, the males also tended to have a larger spleen and bursa of Fabricius 鈥� two organs central to the immune system. The pattern did not hold for organs like the heart and liver not involved the immune system, or for females (Journal of Evolutionary Biology, DOI: 10.1111/j.1420-9101.2004.00805.x).
M酶ller says that females choosing brainy males, perhaps by favouring a large song repertoire, may also be selecting for males with better immune systems.
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Previous research has shown that infections impair a bird鈥檚 cognitive abilities, so a male displaying his braininess may also be showing off good genes for seeing off parasites. What鈥檚 more the pattern may exist in other animals. 鈥淚 can鈥檛 see any reason why it should be restricted to birds,鈥� M酶ller says.
