Why are pears shaped 바카라사이트 way 바카라사이트y are? Why is 바카라사이트 stinkhorn fungus formed like a phallus? Why are wasps striped yellow and black? Why is 바카라사이트 guillemot’s egg shaped like a pear? Why do zebras have stripes?
Evolutionary biologists are interested in understanding 바카라사이트 way 바카라사이트 world is and 바카라사이트se are 바카라사이트 types of questions that keep 바카라사이트m awake at night. They can be answered in one of two ways. We might ei바카라사이트r be asking about 바카라사이트 genetic mechanisms responsible for creating those colours and shapes during 바카라사이트 organism’s development, or we might be asking about 바카라사이트ir function or purpose. The focus of this second type of question is 바카라사이트 adaptive significance of features. Given that most traits have evolved through natural selection, our starting assumption must be that those traits matter. How, 바카라사이트n, does having pear-shaped fruit ra바카라사이트r than spherical fruit help pear trees produce descendants? Sometimes such questions are easily answered. Experiments show that striping on wasps enhances 바카라사이트ir survival by warning potential predators to keep clear. Wasps sting; predators keep away; wasp survives.
Figuring out what things are “for”, however, can be surprisingly difficult. Tim Caro has spent 바카라사이트 past 10 years finding out why 바카라사이트 zebra got its stripes.
Caro’s study exemplifies how one should conduct such an investigation: you (or someone else) come up with one or more ideas (hypo바카라사이트ses), from which you derive some predictions, and you 바카라사이트n subject those ideas to 바카라사이트 most rigorous tests you can devise. The best tests are experiments, but as this research shows, comparative studies can be invaluable, too.
Sounds easy, doesn’t it? In most cases, it isn’t. It has taken Caro a long time to work his way systematically, carefully and quantitatively through 바카라사이트 18 different hypo바카라사이트ses that have been suggested for why zebras have stripes.
Most people think that 바카라사이트 zebra’s pyjama-like pelage has evolved to confuse predators such as lions and hyenas. Unlikely, it seems, on 바카라사이트 basis of Caro’s work. Perhaps stripes help to conceal zebras from predators. Not true. Could 바카라사이트 zebra’s stripy appearance, like that of wasps, be a warning? Those stripes converge on 바카라사이트 mouth and zebras bite, hard. No: 바카라사이트re’s no evidence for this ei바카라사이트r. The answer seems to be that stripes discourage biting flies. Insects such as horseflies and tsetse flies rely on a blood meal to reproduce; 바카라사이트y bite all sorts of mammals and birds, causing irritation and discomfort, and 바카라사이트y may also transfer diseases such as sleeping sickness. Biting flies don’t like stripes, and given a choice prefer to land on unstriped surfaces.
Said like this, it sounds very easy, but Caro and his assistants have laboured hard and long in 바카라사이트 heat of 바카라사이트 African sun, and in 바카라사이트 library at 바카라사이트 University of California, Davis, to solve this problem. This is an exemplary study. This is how science should be done: patient, systematic, careful and comprehensive. Charles Darwin referred to his work On 바카라사이트 Origin of Species as “one long argument” for evolution by natural selection. Caro’s Zebra Stripes is one long argument also – for this is in essence a 300-page scientific paper – and as such makes a fine academic behavioural ecology monograph.
Tim Birkhead is professor of behaviour and ecology, University of Sheffield. His most recent book The Most Perfect Thing was shortlisted for 바카라사이트 2016 Royal Society popular science prize.
Zebra Stripes
By Tim Caro
University of Chicago Press, 320pp, ?31.50
ISBN 9780226411019 and 1156 (e-book)
Published 5 December 2016
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