雅思阅读(达尔文)

Darwin’s Theory of Evolution

①Most educated people in Europe and the Americas during the

19th century had their first full exposure（暴露、公开） to the concept of evolution through the writings of Charles Darwin. Clearly, Darwin did not invent（发明、创造）the idea which had happened long before he was born. However, he carried out the necessary research to conclusively（令人信服的，确凿的） document that evolution has occurred and then made the idea acceptable for scientists and the general public. This was not easy since the idea of evolution had been strongly associated with radical（根本的，基本的） scientific and political views coming out of post-revolutionary France and hence was widely considered to be a threat to

the established social and political order.

②Darwin was influenced by observations made during his youthful voyage（旅行，航海，远行，旅程）as naturalist（自然主义者）on the survey ship Beagle. On the Galapagos Islands（加拉帕戈斯群岛）he noticed the slight variations（变化）that made tortoises from different islands recognizably（可被认识地，可辨别地）distinct. He also observed a whole array of unique finches（雀科鸣鸟）, the famous “Darwin’s finches”（达尔文地雀）, that exhibited（陈列，展览，表现，显示）slight differences from island to island. In addition, they all appeared to resemble（与…相像，类似于）, but

differ from, the common finch on the mainland（大陆，本土）of Ecuador（厄瓜多尔）, 600 miles to the east. Patterns in

the distribution and similarity of organisms（有机物，有机体，生物）had an important influence of Darwin’s thinking.

③Darwin’s theory of evolution entails（牵涉，需要，使必要）the following fundamental ideas. Firstly, species change over time and space. The representatives（代表）of species living today differ from those that lived in the recent past, and populations in

different geographic regions today differ slightly in form or behavior. Secondly, all organisms share common ancestors（祖先）with other organisms. Over time（随着时间的过去）, populations may diverge（分开、偏离） into different species which share a common ancestral（祖先的）population. This means far enough back in time（足够早的时间）, any pair of organisms shares a common ancestor. For example, humans shared a common ancestor with chimpanzees about eight million years ago, with whales about 60 million years ago, and with kangaroos（袋鼠）over 100 million years ago. Thirdly, evolutionary change is gradual and slow in Darwin’s view. This claim（要求，声称）was supported by the long episodes（插曲，片段） of gradual change in organisms in the fossil record and the fact that no naturalist had observed the sudden appearance of a new species in Darwin’s tim e.

④These first three ideas were already under discussion among earlier and contemporaneous（同时期的，同时代的） naturalists working on the “species problem” as Darwin began his research. Darwin’s most original contributions were the mechanism （机制）of natural selection and copious（丰富的，大量

的）amounts of evidence for evolutionary change from many sources, as are demonstrated in his famous book The Origin of Species by Means of Natural Selection published in 1859. Darwin and his fellow naturalist Alfred Wallace independently came to the conclusion that geologically（从地质上来说）older species of life gave rise to geologically younger and different species through the process of natural selection.

⑤Generally speaking, Darwin’s process of natural selection has four components（成分，组分）. The first is variation. That is, organisms within populations exhibit（呈现，证明） individual（个人的，个别的，独特的）variation in appearance and behavior, involving body size, hair color, facial markings, voice properties, or number of offspring. The second is inheritance（遗传，继承）, which means some traits（特性，特点）are heritable and

are consistently passed on from parent to offspring, whereas other traits are strongly influenced by environmental conditions and show weak heritability. The third is high rate of population growth. This

suggests that most populations have more offspring each year than local resources can support, leading to a struggle for resources and consequently（所以，因此）substantial（大量的，牢固的）mortality（死亡数）within each generation. The final component refers to（涉及，指的是，适用于）the differential（差别的） survival and reproduction among species. According to Darwin, individuals possessing traits well suited for the struggle for local resources are more likely to survive and to reproduce, passing those desirable（令人满意的，可取的）variations on to the next generation.

⑥Some variations are helpful. For example, any variation that increases an antelope’s（羚羊）speed may help it elude（逃避，理解不了，抓不到）predators（食肉动物）. Any variation that increases water retention（保留，滞留）in a desert plant will favor survival of that plant to reach maturity（成熟，完备）. Those animals and plants that survive to maturity and are able to reproduce become the parents of the next generation, passing on the favorable variations. Darwin called the process by which such favorable（有利的）variations are passed from generation to generation natural selection.