题型:阅读理解 题类:常考题 难易度:普通
河北省枣强中学2017-2018学年高一下学期英语期末考试试卷
Birds' feathers are some of the most strikingly variable animal characteristics that can be observed by the eyes. The patterns that we see in birds' feathers are made up of combinations of scales, bars, and spots.
We already know why birds have colored feathers. Generally, the color of feathers may protect a bird from being noticed by the enemy in the environment, or it can make a bird more appealing to potential mates by helping them to stand out. These aspects are well known. A greater mystery has been how the patterns are created.
Dr. Ismael Galván and his team studied the color of feathers to see what types of colors were present in birds' complex feather patterns. The study shows they mainly consist of two types of colors: melanin(黑色素), which produce a range of black, grey, brown, and orange color, and carotenoids(类胡萝卜色素), which are used to create brighter colors.
Birds cannot produce carotenoids on their own. For feathers with bright colors, birds must consume food items that contain these paints, and the carotenoids circulate through the blood and to the feather. Melanin, on the other hand, is produced by special cells in the birds' bodies.
The team found that about 32% if the species studied have complex color patterns, with the vast majority of these complex patterns produced by melanin rather than carotenoids. If the birds were artists, they would use carotenoids as a broad brush to produce color patches, with melanin as a detail paint brush to produce more complex designs.
But a few birds are exceptions to this rule: Three bird families do have complex patterns without melanin.
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