Natural Selection and Evolution | 自然选择与进化

📚 Natural Selection and Evolution | 自然选择与进化

Natural selection is a core concept in biology that explains how species change over time. In the Edexcel IGCSE Biology specification, this topic is essential for understanding evolution, adaptation, and the diversity of living organisms.

自然选择是生物学中的核心概念，它解释了物种如何随时间发生变化。在爱德思IGCSE生物考纲中，这一主题对于理解进化、适应以及生物多样性至关重要。

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1. What Is Variation? | 什么是变异？

Variation refers to the differences that exist between individuals of the same species. These differences may be in physical appearance, behaviour, or physiology, and they provide the raw material for natural selection to act upon.

变异指的是同一物种个体之间存在的差异。这些差异可能体现在外貌、行为或生理方面，为自然选择提供了作用的原材料。

Variation can be observed in a whole population of organisms. For example, humans show variation in height, eye colour, and blood type. Without variation, all individuals would be identical, and there would be no chance for some individuals to be better suited to their environment than others.

变异可以在整个生物种群中观察到。例如，人类在身高、眼睛颜色和血型上表现出差异。如果没有变异，所有个体都将完全相同，也就不会有某些个体比另一些个体更适应环境的情况。

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2. Types of Variation | 变异的类型

There are two main types of variation: continuous variation and discontinuous variation. These are distinguished by how the characteristic is inherited and how it appears in a population.

变异主要有两种类型：连续变异和不连续变异。这两种类型根据性状的遗传方式以及在种群中的表现方式来区分。

Continuous variation shows a range of values between two extremes. Examples include height, mass, and skin colour. This type of variation is usually caused by the combined effect of many genes (polygenic inheritance) and is also influenced by the environment.

连续变异在两个极端之间呈现一系列数值。例如身高、体重和肤色。这类变异通常由多个基因共同作用（多基因遗传）引起，并受环境因素影响。

Discontinuous variation falls into distinct categories, with no intermediate values. Examples include blood group, eye colour in some organisms, and the ability to roll one’s tongue. This type of variation is usually controlled by a single gene or a few genes, and the environment has little effect.

不连续变异则分为若干明显类别，没有中间值。例如血型、某些生物的眼睛颜色以及卷舌能力。这类变异通常由单个基因或少数几个基因控制，环境对其影响很小。

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