The tail streamers of male swallows have long been a textbook example of evolutionary ”ornament”. Biologists believed the feathers’ length and shape were determined more by sexual selection – looking pretty to attract a mate – than by classic natural selection for fitness.
But new research challenges this assumption. By assessing the flying skills of swallows, scientists at Exeter and Cambridge universities found that longer tails increased the birds’ aerodynamic manoeuvrability to an unsuspected extent.
In one experiment, swallows with varying tail lengths flew down an 8m ”flight maze” with 400 vertical strings as obstacles. The most aerodynamically agile swallows, with long tail feathers, completed the course in less than two seconds, hitting just one or two strings. The less agile birds took at least three times as long to complete the course.
”Swallow tail streamers are not true ornaments,” says Matthew Evans, the research leader. ”We believe that overall tail length is performing the function of attracting females, but females are choosing between males on the sensible criteria of how good they are at flying and catching prey.”
The research may force biologists to play down the role of sexual selection. Perhaps even the peacock’s tail has a practical function.
Underwater radio rules the waves
Ever since submarines and diving equipment were invented, underwater communications have been a problem. Hand movements and other visual signals have a limited range, and conventional radio waves do not propagate through water. So most marine communications use sound-based acoustic systems, which have serious limitations.
Scottish engineers believe radio may provide a solution after all. Wireless Fibre Systems, a technology company based in Livingston, has discovered how to transmit radio signals through water for several hundred metres. It is embarking on a ₤1.1m project, half funded by the UK government, to develop the technology with two other Scottish companies.
Radio waves are made up of both electric and magnetic components. Terrestrial communications focus on the electric field, says Brendan Hyland, chairman of Wireless Fibre Systems, but the key to successful underwater transmission is to focus on the magnetic field.
Underwater radio offers several advantages over acoustic communication.
For example, radio signals can pass smoothly through the sea and into the air. Also, they are unaffected by noise.
There could be environmental benefits too. Zoologists suspect that underwater acoustic systems are harming whales and other marine mammals - radio waves are less likely to have such an effect.
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Neuroscientists at Cambridge University have confirmed one of the fundamental principles of microeconomics: that people see less value in financial gains as they become richer.
Philippe Tobler and colleagues showed a series of pictures of coins and other objects to a group of young people who had similar educational, but differing financial, backgrounds.
After being told they could keep all the coins they were able to predict correctly, the poorer volunteers learned most quickly to forecast whether a non-monetary image would be followed by a coin.
The results were reflected in fMRI brain scans, which confirmed that neural region activity associated with reward and pleasure was greater in poorer than in wealthier patients.
