📚 IGCSE WJEC Science: Evolution Key Points | IGCSE WJEC 科学：进化 考点精讲
Evolution explains the vast diversity of living organisms on Earth, from single-celled bacteria to giant redwood trees. In your WJEC IGCSE Science course you will need to understand the process of natural selection, the evidence that supports evolution, and real-world examples such as antibiotic resistance. This guide summarises the essential points, the key definitions examiners look for, and the practical examples that appear most often in WJEC papers, so that you can revise efficiently and answer questions with confidence.
进化解释了地球上生物的巨大多样性，从单细胞细菌到高大的红杉树。在 WJEC IGCSE 科学课程中，你需要理解自然选择的过程、支持进化的证据，以及抗生素耐药性等真实案例。本指南总结了关键要点、考官最看重的核心定义，以及 WJEC 试卷中最常出现的实例，帮助你高效复习、自信作答。
1. What is Evolution? | 什么是进化？
Evolution is the gradual change in the inherited characteristics of a biological population over successive generations. It can result in the formation of new species from pre-existing ones. The word 'gradual' matters: evolution is normally measured over hundreds, thousands or even millions of years, not within the lifetime of one organism.
进化是生物种群在连续世代中遗传特征的逐渐变化。它可能导致从已有物种形成新物种。'逐渐'这个词很重要：进化的时间尺度通常是数百年、数千年甚至数百万年，而不是一个生物的一生。
Two terms are essential in WJEC answers. A population is all the individuals of one species living in the same area at the same time. The gene pool is the complete collection of alleles present in that population. Evolution is therefore best described as a change in allele frequency within the gene pool over time.
WJEC 答题中有两个术语必不可少。种群（population）是指同一时间生活在同一区域内的同一物种的全部个体。基因库（gene pool）是该种群中所有等位基因的总和。因此，进化最准确的描述是：基因库中等位基因频率随时间发生改变。
A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring. If two groups can no longer interbreed in this way, they have become separate species.
物种（species）是指具有相似特征、能够相互交配并产生可育后代的生物群体。如果两个群体不再能够这样交配繁殖，它们就已经成为不同的物种。
2. Darwin and the Theory of Natural Selection | 达尔文与自然选择理论
Charles Darwin published On the Origin of Species in 1859, after his voyage on HMS Beagle. His observations of finches and tortoises on the Galapagos Islands were particularly important. Alfred Russel Wallace independently reached very similar conclusions, and the two men presented their ideas together in 1858.
查尔斯·达尔文在乘坐小猎犬号（HMS Beagle）航行之后，于 1859 年出版《物种起源》。他在加拉帕戈斯群岛对地雀和陆龟的观察尤为重要。阿尔弗雷德·华莱士（Alfred Russel Wallace）独立得出了非常相似的结论，两人于 1858 年共同发表了他们的观点。
Darwin's theory rests on four key observations, often called the four pillars of natural selection:
达尔文的理论建立在四个关键观察之上，通常被称为自然选择的四根支柱：
- Overproduction: organisms produce more offspring than the environment can support.
过度繁殖：生物产生的后代数量超过环境所能承载的限度。 - Variation: individuals within a population differ in their characteristics, and much of this variation is inherited.
变异：种群内个体特征各不相同，且这些变异大部分是可遗传的。 - Competition (the 'struggle for existence'): resources such as food, water, shelter and mates are limited, so not all individuals survive.
竞争（'生存斗争'）：食物、水、庇护所和配偶等资源有限，因此并非所有个体都能存活。 - Survival of the fittest: individuals whose characteristics suit the environment better are more likely to survive and reproduce, passing on their advantageous alleles.
适者生存：特征更适应环境的个体更可能存活并繁殖，从而把有利的等位基因传递下去。
Over many generations the advantageous alleles become more common in the gene pool and the disadvantageous ones become rarer. Given enough time and enough genetic change, the population may become a new species.
经过许多世代，有利的等位基因在基因库中变得越来越普遍，而不利的等位基因越来越少见。只要有足够的时间和足够的遗传变化，该种群就可能演变成新的物种。
| Feature | 特征 | Lamarck | 拉马克 | Darwin | 达尔文 |
| Source of variation | 变异来源 | Use and disuse of body parts | 器官的用进废退 | Variation already present in the population | 种群中本来就存在的变异 |
| Inheritance | 遗传方式 | Acquired characteristics are inherited | 获得性性状可遗传 | Only inherited alleles are passed on | 只有可遗传的等位基因被传递 |
| Accepted today? | 今天是否被接受 | No - acquired changes do not alter DNA | 否——获得性改变不会改变 DNA | Yes - supported by DNA and fossil evidence | 是——有 DNA 与化石证据支持 |
3. Variation: The Raw Material for Evolution | 变异：进化的原材料
Without variation, natural selection has nothing to act on. WJEC questions frequently ask you to state the causes of genetic variation and to distinguish it from environmental variation.
没有变异，自然选择就无从作用。WJEC 经常要求你说明遗传变异的来源，并把它与环境变异区分开来。
- Mutation: a random change in the base sequence of DNA that creates new alleles.
基因突变：DNA 碱基序列的随机改变，产生新的等位基因。 - Meiosis: crossing over and independent assortment of chromosomes shuffle alleles into new combinations.
减数分裂：交叉互换与同源染色体的自由组合把等位基因重新洗牌，形成新的组合。 - Random fertilisation: any sperm may fuse with any egg, adding further genetic variety to the offspring.
随机受精：任何精子都可能与任何卵细胞结合，为后代增加更多遗传多样性。
Variation can be continuous, such as height or mass, where individuals show a full range of values. It can also be discontinuous, such as blood group or the ability to roll your tongue, where individuals fall into distinct categories. Environmental variation, such as accent, scars or plant leaf size in different light levels, is not inherited and therefore cannot drive evolution.
变异可分为连续变异，如身高或体重，个体呈现完整的数值范围；也可分为不连续变异，如血型或能否卷舌，个体被划分成不同的类别。环境变异，如口音、疤痕或植物在不同光照下的叶片大小，不会被遗传，因此不能驱动进化。
4. How Natural Selection Works, Step by Step | 自然选择的分步过程
Exam answers gain marks when the process is written as a logical sequence. Use these steps in the correct order and use the correct vocabulary throughout.
考试答案只有按逻辑顺序书写才能得分。请按正确顺序使用以下步骤，并全程使用准确的专业术语。
- 1. A mutation produces a new allele, giving variation within the population.
1. 突变产生新的等位基因，使种群内部出现变异。 - 2. A change in the environment creates a selection pressure, such as a new predator, a new antibiotic or a change in food supply.
2. 环境变化造成选择压力，例如出现新的捕食者、新的抗生素或食物来源改变。 - 3. Individuals with the advantageous allele are more likely to survive and reproduce.
3. 携带有利等位基因的个体更容易存活并繁殖。 - 4. These individuals pass the advantageous allele to their offspring.
4. 这些个体把有利等位基因传给后代。 - 5. The frequency of the advantageous allele in the gene pool increases over many generations.
5. 经过许多世代，有利等位基因在基因库中的频率升高。
The whole process can be summarised in one line:
整个过程可以用一行总结：
ion pressure → Differential survival → Reproduction → Allele frequency changes → Evolution
变异 → 选择压力 → 差别生存 → 繁殖 → 等位基因频率改变 → 进化
5. Evolution Acts on Populations, Not Individuals | 进化作用于种群，而非个体
It is crucial to remember that evolution acts on populations, not on individuals. An organism cannot evolve during its lifetime; changes occur in the gene pool across many generations. A single bacterium does not become resistant because it wants to - it is either born with the resistance allele or it is not.
必须记住，进化作用于种群，而非个体。生物体一生中不可能进化；变化发生在许多代中的基因库里。一个细菌不会因为'想要'就变得耐药——它要么天生带有耐药等位基因，要么没有。
This is why acquired characteristics are not inherited. If you dye your hair or train hard to build muscle, your alleles do not change, so your children will not inherit a new hair colour or your fitness. Only changes to the DNA in gametes can be passed on.
这就是获得性性状不能遗传的原因。如果你染了头发或通过训练练出肌肉，你的等位基因并没有改变，所以你的孩子不会遗传新的发色或你的体能。只有生殖细胞中 DNA 的改变才能传递给下一代。
6. Evidence for Evolution: Fossils | 进化证据：化石
Fossils are the remains or traces of organisms preserved in rocks. They form when hard parts such as bone, shell or teeth are mineralised, or when an organism is trapped in amber, ice or tar. The fossil record shows that simpler organisms appear in older rocks and more complex organisms appear in more recent rocks.
化石是保存在岩石中的生物遗体或痕迹。当骨骼、贝壳或牙齿等坚硬部分被矿物质取代，或生物被困在琥珀、冰层或沥青中时，化石就形成了。化石记录显示：较简单的生物出现在较古老的岩层中，较复杂的生物出现在较新的岩层中。
Relative dating compares the position of rock layers, while radioactive dating uses the decay of isotopes such as carbon-14 or potassium-40 to give an actual age in years. Fossils provide evidence of extinction and of transitional forms, such as Archaeopteryx, which shows both reptile and bird features.
相对测年法比较岩层的位置，而放射性测年法利用碳-14 或钾-40 等同位素的衰变，给出以年为单位的实际年龄。化石为灭绝现象和过渡型生物提供了证据，例如始祖鸟（Archaeopteryx），它同时具有爬行动物和鸟类的特征。
The fossil record is incomplete because many organisms decay completely, because soft-bodied organisms rarely fossilise, and because many fossils have not yet been found or have been destroyed by geological processes.
化石记录并不完整，原因包括：许多生物完全腐解；软体生物很少形成化石；许多化石尚未被发现，或被地质作用破坏。
7. Evidence from Comparative Anatomy and Embryology | 比较解剖学与胚胎学证据
Homologous structures are body parts in different species that have the same basic structure and origin but may have different functions. The pentadactyl limb of a human, a bat, a whale and a horse is the classic WJEC example: the bones are arranged in the same way, but one is used for grasping, one for flying, one for swimming and one for running.
同源结构（homologous structures）是指不同物种中基本结构和起源相同、但功能可能不同的身体部位。人类、蝙蝠、鲸和马的五指（趾）型肢是 WJEC 的经典例子：骨骼排列方式相同，但分别用于抓握、飞行、游泳和奔跑。
Analogous structures, such as the wing of a butterfly and the wing of a bird, have the same function but a different structure and origin. They do not indicate common ancestry. Vestigial structures, such as the human appendix or the pelvis of a whale, are reduced remnants that suggest descent from an ancestor in which they were functional.
同功结构（analogous structures），如蝴蝶的翅膀和鸟的翅膀，功能相同但结构和起源不同，不能说明存在共同祖先。痕迹结构（vestigial structures），如人类的阑尾或鲸的骨盆，是退化的残留部分，暗示它们来自这些结构曾经有功能的祖先。
Embryology gives further support: the embryos of fish, reptiles, birds and mammals are very similar in their early stages, which suggests that they share a common ancestor.
胚胎学提供了进一步支持：鱼类、爬行动物、鸟类和哺乳动物的胚胎在早期阶段非常相似，这暗示它们拥有共同祖先。
8. Evidence from Biochemistry and DNA | 生物化学与 DNA 证据
The strongest modern evidence for evolution comes from DNA. All living organisms use the same genetic code, the same bases A, T, C and G, and the same molecules such as ATP and cytochrome c. This universality strongly suggests that all life shares a common origin.
现代最有力的进化证据来自 DNA。所有生物都使用相同的遗传密码、相同的碱基 A、T、C、G，以及 ATP、细胞色素 c 等相同的分子。这种普遍性强烈暗示所有生命拥有共同起源。
Species that are closely related have more similar DNA base sequences than species that are distantly related. Comparing sequences allows scientists to build evolutionary trees and to estimate how long ago two species diverged, an approach often called the molecular clock.
亲缘关系近的物种，其 DNA 碱基序列相似度高于亲缘关系远的物种。通过比较序列，科学家可以构建进化树，并估算两个物种是在多久以前分化的，这种方法常被称为分子钟。
- Humans and chimpanzees share roughly 98-99% of their DNA sequence.
人类与黑猩猩的 DNA 序列相似度约为 98-99%。 - Fewer differences in a protein such as cytochrome c mean a closer evolutionary relationship.
细胞色素 c 等蛋白质的差异越少，说明进化关系越近。 - Classification systems based on DNA now replace older systems based only on appearance.
基于 DNA 的分类系统如今已取代仅依据外观的旧分类系统。
9. Antibiotic Resistance: Evolution in Action | 抗生素耐药性：正在发生的进化
Antibiotic resistance is the best example of natural selection happening in a human lifetime. Bacteria reproduce very rapidly, sometimes every 20 minutes, so many generations occur in a few days and evolution can be observed directly.
抗生素耐药性是在人类一生中就能观察到的自然选择最佳实例。细菌繁殖非常快，有时每 20 分钟就分裂一次，因此几天内就能经历许多世代，进化可以直接被观察到。
- A random mutation gives some bacteria an allele that makes them resistant to an antibiotic.
随机突变使部分细菌获得对某种抗生素具有耐药性的等位基因。 - The antibiotic acts as a strong selection pressure and kills the non-resistant bacteria.
抗生素成为强大的选择压力，杀死不具耐药性的细菌。 - The resistant bacteria survive, reproduce rapidly and pass on the resistance allele.
耐药细菌存活下来，迅速繁殖并传递耐药等位基因。 - The frequency of the resistance allele in the population increases, so the antibiotic stops working.
耐药等位基因在种群中的频率升高，于是该抗生素失效。
Resistance alleles can also spread between different species of bacteria on plasmids during conjugation, which speeds up the process. MRSA (methicillin-resistant Staphylococcus aureus) and multi-drug resistant tuberculosis are serious clinical examples.
耐药等位基因还可以通过结合过程中质粒在不同细菌物种之间传播，从而加快这一进程。耐甲氧西林金黄色葡萄球菌（MRSA）和耐多药结核病是严重的临床实例。
To slow resistance, patients must complete the full course of antibiotics, doctors should prescribe antibiotics only when necessary, antibiotics should never be used for viral infections such as colds or flu, and antibiotic use in farming should be reduced.
为减缓耐药性，患者必须完成整个疗程；医生只在必要时开抗生素；抗生素绝不用于感冒或流感等病毒感染；同时应减少农业中抗生素的使用。
10. Other Real-World Examples | 其他真实案例
The peppered moth (Biston betularia) is another classic example. Before the Industrial Revolution, pale, lichen-coloured moths were well camouflaged on tree trunks and dark moths were easily seen and eaten by birds.
桦尺蛾（Biston betularia）是另一个经典案例。工业革命之前，浅色、像地衣颜色的蛾子在树干上伪装良好，而深色蛾子容易被鸟类发现并吃掉。
Soot from factories killed the lichens and blackened tree trunks, so the selection pressure reversed: dark moths were now camouflaged and pale moths were eaten. The frequency of the dark allele increased sharply in industrial areas, and has fallen again since clean air legislation.
工厂排放的煤烟杀死地衣并把树干熏黑，于是选择压力发生逆转：深色蛾子此时伪装良好，浅色蛾子被吃掉。在工业区，深色等位基因的频率急剧升高；而在清洁空气法案实施后，它又再次下降。
Pesticide resistance in insects follows exactly the same pattern as antibiotic resistance: spraying kills susceptible insects but leaves resistant mutants, which then breed rapidly and produce a resistant population. Similar reasoning explains the different beak shapes of Darwin's finches on the Galapagos Islands, each suited to a different food source.
昆虫的杀虫剂抗性与抗生素耐药性的模式完全相同：喷洒杀虫剂杀死易感个体，却留下耐药突变体，它们随后迅速繁殖，形成耐药种群。同样的逻辑也解释了加拉帕戈斯群岛上达尔文地雀喙形的差异——每种喙形适应不同的食物来源。
11. Speciation and Extinction | 物种形成与灭绝
Speciation is the formation of a new species. It usually begins when a population becomes isolated, often by a geographical barrier such as a river, mountain range or sea. The two groups then experience different selection pressures and accumulate different alleles.
物种形成（speciation）是指新物种的产生过程。它通常始于种群被隔离，隔离原因常常是河流、山脉或海洋等地理屏障。随后两个群体经历不同的选择压力，积累不同的等位基因。
Over many generations, the two populations become so genetically different that they can no longer interbreed to produce fertile offspring. At this point they are reproductively isolated and are counted as two separate species.
经过许多世代，两个种群在遗传上差异极大，以至于不再能相互交配产生可育后代。此时它们已发生生殖隔离，被视为两个不同的物种。
graphical isolation + Different selection pressures + Reproductive isolation → New species
地理隔离 + 不同选择压力 + 生殖隔离 → 新物种
Extinction occurs when a species has no surviving individuals. It may be caused by environmental change, new predators or competitors, disease, or habitat destruction. Extinction is not a failure of evolution: around 99% of all species that have ever lived are now extinct, and extinction creates vacant niches that surviving species can exploit.
当一个物种不再有存活个体时，就发生了灭绝。原因可能包括环境变化、新的捕食者或竞争者、疾病或栖息地破坏。灭绝并不是进化的失败：曾经存在过的物种中约 99% 已经灭绝，而灭绝会留下空的生态位，供幸存的物种利用。
12. Key Terms and Exam Technique for WJEC | WJEC 关键术语与答题技巧
Learn these definitions word for word, because mark schemes often award a
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