《国家地理》是美国国家地理学会的官方杂志，在国家地理学会1888年创办的九个月后即开始发行。现在已经成为世界上最广为人知的一本杂志，其封面上的亮黄色边框以及月桂纹图样已经成为象征，同时这些标识也是国家地理杂志的注册商标。因此作为美国最具权威的杂志之一，很多题目都有可能从这本杂志中脱颖而出，百利小编根据SAT阅读题目文章类型，特从此处挖掘题源，仅供大家参考学习。

　　一、　题源初现

　　Chameleons Use Built-In Crystals to Change Color

　　Tiny photonic crystals embedded in chameleon skin help the animals achieve their spectacular color change.

　　By Nadia Drake, National Geographic

　　PUBLISHED March 10, 2015

　　Color-changing panther chameleons are among the most disco-ready lizards, courtesy of tiny, built-in crystals that rapidly create multicolored hues.

　　Embedded in the panther chameleon’s skin are not one, but two layers of crystal-containing cells, scientists at Switzerland’s University of Geneva report Tuesday in Nature Communications. Stretching or relaxing the cells helps the animals rapidly change color by changing the color of reflected light. (See more amazing chameleon pictures.)

　　Only adult male panther chameleons (Furcifer pardalis) have a fully developed upper layer of the cells, called iridophores, which they use to put on multihued shows for mating. When the crystals are close together, such as when the animal is relaxed, they reflect blue light. When they are combined with yellow pigments in the chameleon skin, the animal appears green. Stretching the cells and moving the crystals farther apart produces colors ranging from yellow to red.

　　All of the chameleons have a deeper layer of iridophores that reflects a broader spectrum of light, particularly the near-infrared, which is invisible but is close to the wavelengths felt as heat.

　　Scientists speculate that these deeper crystal-containing cells help the cold-blooded animals regulate their body temperature, while the more superficial layer of color-changing cells is involved in camouflage and flashy mating displays. (See photos of insect masters of camouflage.)

　　A male panther chameleon changes color in response to seeing another male. The video is sped up, and includes the animal's starting color in the lower right for comparison.

　　Why It Matters

　　The new study is the first to find two layers of crystal-containing cells in chameleons, each with a potentially different purpose.

　　The different uses suggest that chameleons evolved a double, or even triple, duty for the crystals: efficient camouflage along with spectacular displays and protection from extreme sunlight exposure, says Michel Milinkovitch, one of the study authors.

　　The Big Picture

　　In nature, there are essentially two ways to make something colorful: using pigments, or having a matrix of crystal structures that reflects light. Called photonic crystals, these light reflectors are responsible for the colorful shimmer on butterfly wings, beetles, fish scales, and feathers. (Find out what makes butterflies so colorful.)

　　They also help cephalopods—the ultimate masters of camouflage—blend into their undersea environment. (See more photos of undersea camouflage.)

　　Pigments can fade, but structural color retains its sheen until the underlying crystals are destroyed.

　　What's Next

　　Milinkovitch and colleagues note that although they’ve been able to demonstrate that chameleons can tune these crystal-containing cells, they still don’t know exactly how they do it.

　　While they figure out how chameleons control their crystals, other scientists are mimicking natural color-generating nanoarchitectures in the laboratory to produce materials such as paints and fabrics with everlasting color.

　　二、文章大意

　　这篇文章主要针对变色龙皮肤的变化进行了探讨，首先作者提出了变色龙皮肤变化的原因是因为其皮肤内部含有两层含晶体细胞，这种细胞可以让这种生物通过反射光线的颜色来改变自身皮肤的颜色。之后作者又给出了变色龙变换皮肤颜色的原因以及人类通过研究对将这种现象运用到人类生活当中。

　　三、疑难词汇总

　　chameleons: n. 变色龙

　　pigments: n.色素

　　near-infrared: 近红外

　　wavelengths: n. [物] 波长

　　matrix: [生物][地质] 基质;母体

　　photonic: adj. 光激性的

　　cephalopods: n. 头足类动物

　　sheen: n. 光辉，光泽，光彩