2017-02-01. Finding the Speed of Evolution in a Study of Bird Beaks.

posted Feb 1, 2017, 4:19 PM by Alan Gould
By Steph Yin, The New York Times. For GSS Losing Biodiversity chapter 3. Excerpt: When the ancestors of Darwin’s finches arrived on the Galápagos two million years ago, they gained access to a world of new morsels, untapped by other animals. In a relatively short period, 14 species of finches evolved, specializing in different diets through different beak shapes: short for crushing seeds, sharp for catching insects, long for probing cactus flowers and so on. This rapid diversification in the presence of new opportunity is called adaptive radiation. Studies of small island bird and lizard populations describe a fast burst of evolution, followed by a slowdown. But broader research has failed to find this fast-then-slow pattern of evolution on a global scale. ...In the case of birds, it is not that evolution slows over time, but rather it switches from generating major changes in beak shape to producing smaller iterations of the same basic shapes, said Gavin Thomas, a professor of animal and plant sciences at the University of Sheffield in Britain and an author of the paper. In their study, Dr. Thomas and collaborators collected 3-D scans of bird beaks from museum specimens representing more than 97 percent of present-day birds. Through a website called Mark My Bird, they asked the public to help mark out specific features on the scans, including the tip, midline and curvature of each bill. ...the scientists were able to infer ancestral bill shapes and rates of evolution going back more than 80 million years. Their data suggested that most of the variation we see in beaks today evolved long ago, in a relatively short period of time....  https://www.nytimes.com/2017/02/01/science/birds-beaks-evolution.html