IGCSE WJEC Biology: Speciation | IGCSE WJEC 生物：物种形成考点精讲

📚 IGCSE WJEC Biology: Speciation | IGCSE WJEC 生物：物种形成考点精讲

Speciation is a fundamental concept in evolutionary biology that explains how new species arise from existing ones. For the WJEC IGCSE Biology specification, you must understand the definition of a species, the role of isolating mechanisms, and the process of allopatric speciation, supported by the classic example of Darwin’s finches. This revision guide breaks down every key point with clear bilingual explanations, ensuring you are fully prepared for exam questions on this topic.

物种形成是进化生物学的一个基本概念，它解释了新物种如何从现有物种中产生。根据 WJEC IGCSE 生物学大纲，你必须理解物种的定义、隔离机制的作用以及异域物种形成的过程，并掌握达尔文雀这一经典实例。本精讲文章将以中英双语的清晰解释拆解每一个关键点，确保你为相关考题做好充分准备。

1. What is a Species? | 什么是物种？

In everyday language, a species is a group of living organisms consisting of similar individuals capable of reproducing. However, in biology, a more precise definition is needed. A species is commonly defined as a group of organisms that can interbreed in nature to produce viable, fertile offspring. Members of the same species share a common gene pool and are reproductively isolated from other such groups.

在日常用语中，物种是一组由相似个体组成的生物，它们能够繁殖。但在生物学中，需要更精确的定义。物种通常被定义为在自然条件下可以交配并产生可存活、可育后代的一群生物。同一物种的成员共享一个共同的基因库，并与其他这类群体存在生殖隔离。

2. The Biological Species Concept | 生物物种概念

The biological species concept, proposed by Ernst Mayr, focuses on reproductive compatibility. According to this concept, whether two organisms belong to the same species depends on whether they can produce fertile offspring. If a horse and a donkey mate, they produce a mule, which is sterile. Therefore, horses and donkeys are classified as separate species. This concept is central to understanding speciation.

由恩斯特·迈尔提出的生物物种概念重点关注生殖兼容性。根据这一概念，两个生物是否属于同一物种取决于它们能否产生可育后代。如果马和驴交配，它们会产生骡子，而骡子是不育的。因此，马和驴被归类为不同的物种。这一概念对于理解物种形成至关重要。

3. Speciation Defined | 物种形成定义

Speciation is the evolutionary process by which populations evolve to become distinct species. It occurs when a single ancestral species splits into two or more descendant species that are reproductively isolated from each other. The key driving force is the accumulation of genetic differences over generations, often reinforced by natural selection acting in different environments.

物种形成是指种群通过进化成为不同物种的演化过程。当一个祖先物种分裂成两个或更多彼此生殖隔离的后代物种时，物种形成便发生了。关键的驱动力是在世代中积累遗传差异，通常由在不同环境中起作用的自然选择所强化。

4. Reproductive Isolation: The Key to Speciation | 生殖隔离：物种形成的关键

For speciation to occur, gene flow between populations must be prevented. Reproductive isolating mechanisms are biological features that prevent different species from interbreeding. They are categorised into pre-zygotic barriers, which act before fertilisation, and post-zygotic barriers, which act after fertilisation. Both types ensure that species remain genetically distinct.

要发生物种形成，种群间的基因流动必须被阻止。生殖隔离机制是阻止不同物种杂交的生物学特征。它们分为在受精前起作用的合子前隔离，以及在受精后起作用的合子后隔离。这两种类型都确保物种在遗传上保持独特。

5. Pre-zygotic Isolating Mechanisms | 合子前隔离机制

Pre-zygotic barriers prevent mating or fertilisation between species. The table below summarises the main types, each with a brief description and example. These barriers are the first line of defence against gene flow, and they often involve differences in behaviour, timing or structure.

合子前隔离机制阻止物种之间的交配或受精。下表总结了主要类型，每种给出简要描述和实例。这些障碍是阻止基因流动的第一道防线，通常涉及行为、时间或结构上的差异。

Pre-zygotic Barrier	合子前隔离	Description and Example	描述与实例
Habitat isolation	栖息地隔离	Species live in different habitats within the same area; e.g. two species of garter snakes, one aquatic and one terrestrial.	同一地区的不同栖息地；例如两种束带蛇，一种水生，一种陆生。
Temporal isolation	时间隔离	Species breed at different times of day or year; e.g. three species of orchid that release pollen on different days.	繁殖时间不同；例如三种兰花在不同日期释放花粉。
Behavioural isolation	行为隔离	Differences in courtship rituals prevent mating; e.g. distinct mating dances of blue-footed boobies.	求偶仪式不同；例如蓝脚鲣鸟独特的求偶舞蹈。
Mechanical isolation	机械隔离	Reproductive structures are incompatible; e.g. differently shaped snail shells prevent effective copulation.	生殖结构不兼容；例如不同形状的蜗牛壳阻止有效交配。
Gametic isolation	配子隔离	Sperm cannot fertilise egg; e.g. in sea urchins, sperm proteins fail to bind to egg surface molecules.	精子无法使卵子受精；例如海胆中精子蛋白无法与卵子表面分子结合。

6. Post-zygotic Isolating Mechanisms | 合子后隔离机制

Post-zygotic barriers reduce the viability or fertility of hybrid offspring. Even if fertilisation occurs, the resulting hybrid may fail to develop, be weak or sterile. This prevents the hybrid genes from spreading back into the parent populations, maintaining species separation.

合子后隔离机制降低杂交后代的存活率或繁殖力。即使受精成功，产生的杂种可能无法发育、弱小或不育。这阻止了杂种基因传播回亲本种群，从而维持物种分离。

Post-zygotic Barrier	合子后隔离	Description and Example	描述与实例
Hybrid inviability	杂种不活	Hybrid embryo dies early; e.g. some frog crosses produce embryos that do not survive beyond early cleavage.	杂种胚胎早期死亡；例如某些蛙类杂交产生的胚胎在卵裂早期便死亡。
Hybrid sterility	杂种不育	Hybrid is healthy but sterile; e.g. mule (horse × donkey) cannot reproduce.	杂种健康但不育；例如骡子（马×驴）无法繁殖。
Hybrid breakdown	杂种衰败	First-generation hybrids are fertile but second-generation offspring are weak or sterile; e.g. some rice hybrids show reduced vigour in later generations.	第一代杂种可育，但第二代后代弱小或不育；例如某些水稻杂种在后代中表现出活力下降。

7. Allopatric Speciation: Geographic Separation | 异域物种形成：地理隔离

The most common mode of speciation is allopatric speciation, where a physical barrier splits a population into geographically isolated groups. Barriers can be mountain ranges, rivers, deserts, or oceans formed by continental drift. Once separated, the two populations experience different selection pressures, and genetic drift can also cause random changes. Over many generations, they diverge to the point where they can no longer interbreed, even if the barrier is removed.

最常见的物种形成模式是异域物种形成，即物理屏障将一个种群分割成地理上隔离的群体。屏障可以是山脉、河流、沙漠或因大陆漂移形成的海洋。一旦分离，两个种群将经历不同的选择压力，而遗传漂变也会引起随机变化。经过许多代，它们的分化程度达到即使移除屏障也无法再相互交配的地步。

8. Steps of Allopatric Speciation | 异域物种形成的步骤

The process can be broken down into a clear sequence of events, which you must be able to describe in exam answers. Follow the steps logically to show how a new species arises from a single ancestral population.

该过程可以分解为一系列清晰的事件，你必须在考试答案中能够描述这些步骤。按照逻辑描述如何从一个祖先种群产生新物种。

Step 1: Geographical isolation. A physical barrier divides a continuous population. Members can no longer move freely and gene flow is interrupted.

步骤1：地理隔离。 物理屏障将一个连续的种群分隔开。成员不能自由移动，基因流中断。

Step 2: Different environmental pressures. The two isolated populations experience different climatic conditions, food sources, predators or diseases. Natural selection favours different traits in each environment.

步骤2：不同的环境压力。 两个隔离种群经历不同的气候条件、食物来源、捕食者或疾病。自然选择在各自环境中青睐不同的性状。

Step 3: Accumulation of genetic differences. Over many generations, mutations, natural selection and genetic drift cause the gene pools of the two populations to diverge. Allele frequencies shift independently.

步骤3：遗传差异的累积。 经过许多代，突变、自然选择和遗传漂变导致两个种群的基因库产生分化。等位基因频率各自变化。

Step 4: Reproductive isolation. The genetic differences become so substantial that even if the barrier disappeared, individuals from the two populations would either not mate or, if they did, would produce infertile or nonviable offspring. At this stage, speciation is complete.

步骤4：生殖隔离。 遗传差异变得如此显著，以至于即使屏障消失，来自两个种群的个体要么不会交配，要么即使交配也会产生不育或无活力的后代。此时物种形成完成。

9. Darwin’s Finches: A Classic Example | 达尔文雀：经典实例

Darwin’s finches on the Galápagos Islands provide a powerful illustration of allopatric speciation. A small population of finches from the South American mainland originally colonised one island. Over time, birds dispersed to other islands, each with slightly different environments. Geographic isolation between islands prevented interbreeding. On each island, natural selection shaped beak size and shape according to the main food source—large, thick beaks for cracking seeds, slender beaks for catching insects. Eventually, the populations diverged so much that they became separate species, unable to interbreed when they later came into contact.

加拉帕戈斯群岛上的达尔文雀为异域物种形成提供了有力的例证。来自南美大陆的一小群雀鸟最初定居在一个岛屿上。随着时间的推移，鸟类传播到其他岛屿，每个岛屿的环境略有不同。岛屿之间的地理隔离阻止了杂交。在每个岛上，自然选择根据主要食物来源塑造了喙的大小和形状——大而厚的喙用于咬碎种子，细长的喙用于捕食昆虫。最终，这些种群的差异如此之大，以至于它们成为了独立的物种，即使后来再次接触也无法交配。

Exam tip: When using this example, always mention geographical isolation, different selection pressures, divergence of beak traits, and the final reproductive isolation.

考试提示： 在使用这个例子时，务必提及地理隔离、不同的选择压力、喙性状的分化以及最终的生殖隔离。

10. Importance of Speciation in Evolution | 物种形成在进化中的重要性

Speciation is the engine of biodiversity. Without it, there would be no new species, and the tree of life would not branch. Each speciation event increases the number of distinct species, contributing to the variety of life we see today. Understanding speciation also helps scientists conserve species by identifying distinct populations that may be in the process of becoming new species.

物种形成是生物多样性的引擎。没有它，就不会有新物种产生，生命之树也不会分枝。每一次物种形成事件都会增加独特物种的数量，为我们今天看到的生命多样化做出贡献。理解物种形成也有助于科学家通过识别可能正在形成新物种的独特种群来保护物种。

11. WJEC IGCSE Exam Tips for Speciation | WJEC IGCSE 物种形成考试技巧

Exam questions on speciation often ask you to explain the process step by step and apply it to a given example. Use precise terminology: ‘geographical isolation’, ‘gene flow’, ‘reproductive isolation’, ‘natural selection’, and ‘speciation’. Structure your answer in a logical sequence. If a question provides a scenario, explicitly link each step to the information given.

关于物种形成的考题经常要求你逐步解释该过程，并将其应用于给定的例子。使用精确术语：“地理隔离”、“基因流”、“生殖隔离”、“自然选择”和“物种形成”。按逻辑顺序组织答案。如果题目提供了一个情景，明确将每一步与所给信息联系起来。

Because WJEC mark schemes reward the mention of geographical isolation leading to separate gene pools and different selection pressures, always highlight these points. For example, you might write: ‘The population was split by a river (geographical isolation). The two groups experienced different food sources (different selection pressures), leading to different advantageous traits. Over time, they became so different that they could no longer interbreed (reproductive isolation), resulting in a new species.’

由于 WJEC 的评分方案奖励提及地理隔离导致独立的基因库和不同选择压力，一定要突出这些要点。例如，你可以这样写：“种群被一条河流隔开（地理隔离）。这两个群体经历了不同的食物来源（不同的选择压力），从而导致不同的有利性状。随着时间的推移，它们变得如此不同，以至于无法再交配（生殖隔离），从而形成了一个新物种。”

Additionally, many questions ask you to interpret data about beak size or mating preferences. Practise linking these to the concepts of isolation and divergence. Remember that a new species is not formed overnight—speciation usually occurs over thousands of generations.

此外，许多题目要求你解释关于喙大小或交配偏好的数据。练习将这些与隔离和分化的概念联系起来。记住，新物种不是一夜之间形成的——物种形成通常发生在数千代的时间里。

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IGCSE WJEC Biology: Speciation | IGCSE WJEC 生物：物种形成 考点精讲