话题20 自然生态-2020高考英语【试吧大考卷】高中全程训练计划

话题二十　自然生态 A [2019·太原市高三阶段性测评] Where there are humans, there are house sparrows. But despite their suggestive species name, Passer domesticus, they aren't officially domesticated. The bold, tiny and gray­and­brown birds are found on every continent except Antarctica, hopping around cities, pecking(啄)at leftover food on sidewalks, and sometimes chasing away native bird species. The house sparrows have adapted to living alongside humans, but this friendly behavior to humans is legendary. No one knew what set them apart from the other wild members of the sparrow family. Looking for a genetic explanation, Mark Ravinet, an evolutionary biologist and his colleagues caught dozens of sparrows at sites across Europe. They set up mist nets that harmlessly trapped the birds as they flew inside — measured and tagged the birds, drew blood samples, and then released them. Back in the lab, they sequenced the birds' DNA. They found that the house sparrow's genes of many regions appeared to have experienced positive selection, helping the birds live alongside humans. The evolutionary process of natural selection may have favored genetic changes that altered their skull shape and allowed them to eat food with starch (淀粉) — similar to domesticated animals like dogs. The most significant sign of positive selection in the birds' DNA was found in a region with two known genes: one is linked to skull development and another helps create the amylase(淀粉酶), which helps break down starch in humans, dogs and other domesticated animals. Changes to both genes might have helped the house sparrows eat human­cultivated foods. Another evolutionary biologist Samuel Andrew says the work is an exciting new step for bird researchers that could answer many questions about how sparrow species adapted to different conditions. But he and Ravinet agree there may be changes to other genes that were missed in this initial analysis, yet still helped the birds take advantage of humans.[来源:Z+xx+k.Com] “If