TOEFL 9.13考试真题小剧场来啦，想要第一手、最新最全托福考场真题解析，记得锁定我们！

今天给大家带来托福考场真题小剧场之—— Speciation–物种形成篇。

Part 1 考点概述

Part 2 考点精析

Speciation: 物种形成

Speciation: 物种形成，又称为种化，是演化的一个过程，指生物分类上的物种诞生。

物种形成是新物种从旧物种中分化出来的过程，即从一个种内产生出另一个新种的过程，包括三个环节：突变以及基因重组为进化提供原料，自然选择是进化的主导因素，隔离是物种形成的必要条件。

往往导致物种形成主要有以下原因：海洋、高山、沙漠等地理隔离(Geographical isolation)；动物因求偶方式、繁殖期不同，植物因开花季节、花的形态不同等等。

在托福考试当中，阅读和听力部分曾多次考查过关于物种地理隔离的文章。

例如：

阅读TPO 31-P1 Speciation in Geographically Isolated Populations

阅读TPO 42-P3 Geographic Isolation of Species

听力ZTO17-S2

9.4口语真题

地理隔离作为托福考试中最高频的考点之一也意味着我们要对其背景知识做到充分了解。做过充分准备的同学，对于再次遇到相关考试内容，一定会更加得心应手。因此，今天的话题，我们一起来讨论地理隔离

地理隔离的概述

地理隔离：同一种生物由于地理上的障碍而分成不同的种群，使得种群间不能发生基因交流的现象。群体生活在不同的栖息地，彼此不能相遇。海洋、大片陆地、高山和沙漠等，阻碍了生物的自由迁移、交配、基因交流，最后就形成为独立的种群。

地理隔离导致生殖隔离，不同物种之间由于基因不同而不能交配。并根据具体的地理环境不同，逐渐向不同方向进化。

影响物种进化的方式：地理隔离——自然选择不同——进化方向不同——产生差异——生殖隔离——新物种

地理隔离所形成的物种被称为异域物种，allopatric speciation形成。

下面一起来看看例题

节选自TPO 31-P1 Speciation in Geographically Isolated Populations：

1️⃣Evolutionary biologists believe that speciation, the formation of a new species, often begins when some kind of physical barrier arises and divides a population of a single species into separate subpopulations. Physical separation between subpopulations promotes the formation of new species because once the members of one subpopulation can no longer mate with members of another subpopulation, they cannot exchange variant genes that arise in one of the subpopulations.

2️⃣In the absence of gene flow between the subpopulations, genetic differences between the groups begin to accumulate. Eventually the subpopulations become so genetically distinct that they cannot interbreed even if the physical barriers between them were removed.

3️⃣At this point the subpopulations have evolved into distinct species. This route to speciation is known as allopatry (“allo-” means “different”, and “patria” means “homeland”).

节选自TPO 42-P3 Geographic Isolation of Species：

In the formation of many species, the initial isolation of a population seems to have been a geographic barrier. This mode of evolving new species is called allopatric speciation.

选自听力ZTO17-S2：

One cause of speciation is when a barrier divides a population of organisms into two groups. Barriers either directly or indirectly interrupt the flow of genes within the population.

9.4真题：

The most common ways, the introduction of a physical barrier, a geographic obstacle that ends up overtime to divide one species into two separate groups. As the barrier grows and forms, it becomes harder for the two groups change for mingle to the point that eventually they are only able to reproduce separately within their own separate routes. And they begin to develop their own unique characteristics after several generations, eventually evolving into two species.

配合题目：选自TPO 42-P3-3，Geographic Isolation of Species

Q：According to paragraph 1, allopatric speciation is possible when

A. a population contains all the different genes present in a species at a particular time

B. a population becomes isolated due to the presence of a geographic barrier

C. genetic mixing begins to occur in previously separate populations of a species

D. a species is successful in crossing a geographic barrier

地理隔离原因

许多因素可以在地域上隔离一个种群，例如地壳运动(crustal movement)、冰川移动(Glacier movement )等。某些山脉的出现会逐渐分离出一个只能在低洼的湖泊中生活的物种，某些鱼类可能就这样被隔离出来了。

同样，移动的冰川可能会逐渐将一个种群分开。

或者形成像巴拿马地峡这样的大陆桥，将海洋生物隔离在大陆桥的两边水域。地质运动形成了连接北美和南美的大陆桥，即巴拿马地峡。

之前，大陆间的这个缺口可以让水自由流动，而现在巴拿马地峡在大西洋和太平洋之间形成了一道障碍。这个地域分割为鱼和其他海洋物种的异域性物种形成创造了条件。

节选自TPO 42-P3 Geographic Isolation of Species：

Many factors can isolate a population geographically. A mountain range may emerge and gradually split a population of organisms that can inhabit only lowland lakes, certain fish populations might become isolated in this way. Similarly, a creeping glacier may gradually divide a population, or a land bridge such as the Isthmus of Panama may form and separate the marine life in the ocean waters on either side.

节选自TPO 31-P1 Speciation in Geographically Isolated Populations：

About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama . While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. This division set the stage for allopatric speciation among populations of fishes and other marine species.