【直播回听】英语听力Day20

【精听】听一分半左右的音频，逐句听写，跟读

今天的比较难所以附上英文原文，可以比照着听。

Human populations near the equator haveevolved dark skin over many generations because of exposure to the fierce raysof the Sun. A similar phenomenon has also occurred in other parts of the animalkingdom. The African grass mouse is a good example. Most mice are nocturnal,but the African grass mouse is active during daylight hours. This means that itspends its days searching for food in the semidry bush and scrub habitats ofeastern and southern Africa. Its fur is striped, like a chipmunk's, which helpsit blend in with its environment. Because it spends a lot of time in theintense tropical sun, the grass mouse has also evolved two separate safeguardsagainst the Sun's ultraviolet radiation. First, like the populations of humansin this region of the world, the skin of the grass mouse contains lots ofmelanin, or dark pigment. Second, and quite unusual, this mouse has a layer ofmelanin-pigmented tissue between its skull and skin. This unique"cap" provides an extra measure of protection for the grass mouse andthree other types of African mouse-like rodents that are active during the day.The only other species scientists have identified with the same sort of skulladaptation is the white tent-making bat of the Central American tropics.Although these bats sleep during the day, they do so curled up with their headsexposed to the sun.