SOMETIMES, scientific results come from the most unlikely places. The aftermath of the Chernobyl nuclear accident, for example, might reasonably be expected to have revealed the effects of radiation on health. That it casts light on the theory of sexual selection as well is a bit of a surprise.

That, nevertheless, is the inference of a paper by Anders Moller of Pierre & Marie Curie University in Paris, and Timothy Mousseau of the University of South Carolina. Dr Moller and Dr Mousseau have been looking at bird life around the wrecked reactor. One of their conclusions, just published in the Journal of Applied Ecology, is that colourful species have done less well than dull ones. Since colourful plumage is almost always a sexual signal, understanding why is instructive.

The data come from a census of 57 bird species that the researchers carried out in the area affected by the radioactive plume from the accident. When due allowance was made for habitat differences, they found that species which relied on a class of chemicals called carotenoids to tint their feathers fared worse when there was more radioactivity around. Intriguingly, that did not apply to birds that used melanin, another pigment, in their plumage, nor to those that employed iridescence—which is a result of the structure of feathers, rather than their chemistry.

Besides acting as pigments, carotenoids are antioxidants that have an important role in protecting DNA from harm. One of the ways that radiation causes harm is by generating molecules that promote oxidation, so a good supply of carotenoids protects against such damage. Using them to make feathers pretty instead of mopping up oxidative molecules thus has a significant cost—as this result shows.

The reason this is interesting is that there is a debate in biology between those who think signals such as flashy feathers are essentially arbitrary and those who think they are signs of underlying health and good genes. Dr Moller's and Dr Mousseau's result shows that the bright reds and yellows of carotenoid-based plumage really do come at a price, and thus indicate underlying health. The unusual circumstances of Chernobyl have exposed that price to human observers, but it will have to be paid all the time, even in places that have not fallen foul of radioactive plumes.

The costs of melanin-based plumage and iridescence are clearly different from this. No doubt they exist, but it would be nice to think that the experiment needed to expose them is not quite so drastic as an exploding reactor.