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Sparrow weavers: Social status determines extent of sex differences

Thumbnail for version as of 21:49, 30 April 2010
White-browed sparrow weaver/Valentina

At ScienceDaily, we learn that while “the brains of all vertebrates display gender-related differences,”

Researchers at the Max Planck Institute for Ornithology in Seewiesen have now demonstrated for the first time in the white-browed sparrow weaver, an African songbird, that the extent of these sex differences in the brain varies according to social status, and cannot be explained by singing behaviour as previously thought.

Essentially, only the dominant male in the small flock mates, and during the breeding season, “sings a long and complex solo song that it only performs at dawn.”

According to the hitherto accepted hypothesis, the structural sex differences in the brains are largest in species in which singing behaviour also varies significantly between males and females or in which only the males sing.

Researchers were surprised to discover that the sex difference they observed varied with the social status of the birds.

The findings of the various male-female comparisons do not coincide with the accepted view of the regulation of sex differences in the brain and behaviour. If it is assumed that the greater number of neurons found in the brain of the dominant males is necessary for the singing of the complex solo song, then the sex difference in the brains of the subordinate males and females cannot be explained. Alternatively, it is possible that the determining factor here is not the brain area size, but the varying gene activity. “This would mean, however, that once a male has climbed to the top of the hierarchy, it produces the duet song with neurons that show different gene activity than those of the females and subdominant males,” says Cornelia Voigt.

If an actual history, straightened out, is this complex, postdicting what past species did – based on “the assured results of evolutionary theory” – should be something like The Weavers: A Novel.


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