托福阅读文章中的物种灭绝.pdf

智 课 网 托 福 备 考 资 料 托福阅读文章中的物种灭绝 如今托福阅读的背景知识要求越来越多，托福阅读题材也越来越广 泛，如果大家不能在新托福阅读的复习时对各种资料有一个了解的话考 试的时候会很困难，下面的材料是关于物种的自然灭绝的现象，希望对 大家有帮助。 新托福阅读准备之托福阅读题材：关于物种的自然灭绝 托福阅读原文： Natural selection acts solely through the preservation of variations in some way advantageous, which consequently endure. Owing to the high geometrical rate of increase of all organic beings, each area is already fully stocked with inhabitants; and it follows from this, that as the favoured forms increase in number, so, generally, will the less favoured decrease and become rare. Rarity, as geology tells us, is the precursor to extinction. We can see that any form which is represented by few individuals will run a good chance of utter extinction, during great fluctuations in the nature of the seasons, or from a temporary increase in the number of its enemies. But we may go further than this; for, as new forms are produced, unless we admit that specific forms can go on indefinitely increasing in number, many old forms must become extinct. That the number of specific forms has not indefinitely increased, geology plainly tells us; and we shall presently attempt to show why it is that the number of species throughout the world has not become immeasurably great. We have seen that the species which are most numerous in individuals have the best chance of producing favourable variations within any given period. We have evidence of this, in the facts stated in the second chapter showing that it is the common and diffused or dominant species which offer the greatest number of recorded varieties. Hence, rare species will be less quickly modified or improved within any given period; they will consequently be beaten in the race for life by the modified and improved descendants of the commoner species. From these several considerations I think it inevit