Evolution | 进化

📚 Evolution | 进化

Evolution is the change in heritable characteristics of biological populations over successive generations. For Cambridge A-Level Biology, evolution is best understood as a change in allele frequencies in a gene pool. It explains both the unity and diversity of life and is central to topics such as variation, selection, speciation and classification.

进化是指生物种群的可遗传特征在连续世代中发生改变。在剑桥A-Level生物课程中，进化最好理解为基因库中等位基因频率的变化。它解释了生命的统一性和多样性，是变异、选择、物种形成和分类等主题的核心。

1. Variation and Its Sources | 变异及其来源

Evolution requires heritable variation among individuals in a population. If all individuals were genetically identical, selection could not cause a change in allele frequencies across generations.

进化需要种群内个体之间存在可遗传的变异。如果所有个体在遗传上完全相同，选择就无法引起等位基因频率在世代间的变化。

Heritable variation arises mainly from mutation, meiosis and random fertilisation. Mutation creates new alleles; crossing over and independent assortment during meiosis reshuffle existing alleles; random fertilisation produces new allele combinations.

可遗传变异主要来源于突变、减数分裂和受精过程的随机性。突变产生新等位基因；减数分裂中的交叉互换和独立分配重组已有等位基因；受精随机性产生新的等位基因组合。

Only mutations in germ-line cells can be inherited; mutations in body cells affect only that individual.

只有生殖细胞中的突变可以遗传；体细胞突变只影响该个体本身。

2. Natural Selection | 自然选择

Natural selection is a non-random process in which individuals with phenotypes better suited to their environment are more likely to survive and reproduce. This leads to an increase in the frequency of favourable alleles over generations.

自然选择是一个非随机过程，表型更适合环境的个体更可能存活和繁殖。这导致有利等位基因的频率在世代间增加。

Natural selection requires overproduction of offspring, variation, competition for limited resources, differential survival and reproduction, and inheritance of favourable alleles.

自然选择需要后代过多、存在变异、对有限资源的竞争、存活和繁殖的差异以及有利等位基因的遗传。

Selection acts on phenotypes, but its evolutionary consequence is a change in the gene pool. An adaptation is any inherited trait that increases an organism’s fitness.

选择作用于表型，但其进化后果是基因库的改变。适应是指任何能提高生物体适合度的可遗传性状。

3. Types of Selection | 选择类型

Stabilising selection favours intermediate phenotypes and removes extreme phenotypes. It reduces variation and keeps the population mean stable; human birth weight is a classic example.

稳定选择青睐中间表型，淘汰极端表型。它降低变异幅度并使种群平均值保持稳定；人类出生体重是一个经典例子。

Directional selection favours one extreme phenotype, shifting the population mean. Examples include the evolution of antibiotic resistance and melanism in the peppered moth.

方向选择青睐某一个极端表型，使种群平均值发生移动。例子包括抗生素耐药性的进化和桦尺蛾的黑化。Published by TutorHao | A-Level Biology Revision Series | aleveler.com

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