Evolution and Natural Selection进化与自然选择

• Fossil record:化石记录： fossils show a progression of forms through geological time; transitional fossils link major groups (e.g., Archaeopteryx between dinosaurs and birds).化石展示地质时间中生物形态的演变序列；过渡化石连接主要类群（如始祖鸟连接恐龙与鸟类）。
• Comparative anatomy — homologous structures:比较解剖学 — 同源结构： structures with similar underlying anatomy but different functions (e.g., human arm, bat wing, whale flipper) indicate a common ancestor.具有相似基本解剖结构但功能不同的结构（如人臂、蝙蝠翼、鲸鳍）表明存在共同祖先。
• Analogous structures (convergent evolution):同功结构（趋同进化）： superficially similar structures in unrelated organisms (e.g., dolphin and shark fins) evolved independently; similar environment, not common ancestry.无亲缘关系的生物中表面相似的结构（如海豚与鲨鱼的鳍）独立演化；反映相似环境而非共同祖先。
• Vestigial structures:痕迹器官： reduced or non-functional remnants of structures that were functional in ancestors (e.g., human coccyx, whale pelvic bones). Evidence of descent with modification.在祖先中有功能、现已退化或无功能的结构遗迹（如人类尾骨、鲸鱼骨盆骨）。为后裔有改变的证据。
• Molecular / DNA evidence:分子/DNA 证据： more closely related species share more similar DNA sequences and protein structures; mitochondrial DNA and cytochrome c sequences have been used to build phylogenetic trees.亲缘关系越近的物种 DNA 序列与蛋白质结构越相似；线粒体 DNA 与细胞色素 c 序列已用于构建系统发育树。
• Biogeography:生物地理学： the geographic distribution of species matches evolutionary history; island species resemble nearby mainland species more than geographically distant species (e.g., Darwin's finches in the Galápagos).物种的地理分布与进化历史相符；岛屿物种与邻近大陆物种更相似，而非与地理上遥远的物种相似（如加拉帕戈斯的达尔文雀）。

• Overproduction (potential for population increase):过度繁殖（种群数量增长潜力）： organisms produce more offspring than can survive. Resources are limited; not all offspring can live to reproduce.生物产生的后代多于能存活的数量。资源有限，并非所有后代都能存活并繁殖。
• Heritable genetic variation:可遗传的遗传变异： individuals in a population differ from one another in traits, and those traits can be passed to offspring (via genes/alleles). Mutation and sexual reproduction are the sources.种群中个体在性状上互有差异，且这些性状可遗传给后代（通过基因/等位基因）。突变与有性生殖是来源。
• Competition (struggle for existence):竞争（生存竞争）： individuals compete for limited resources (food, mates, space). Not all individuals survive and reproduce equally.个体为有限资源（食物、配偶、空间）而竞争。并非所有个体都能同等地存活与繁殖。
• Differential survival and reproduction (natural selection):差异存活与繁殖（自然选择）： individuals whose heritable traits make them better suited to their environment tend to survive longer and leave more offspring. Over generations, advantageous alleles increase in frequency in the population.遗传性状使其更适应环境的个体倾向于存活更长时间并留下更多后代。经过若干代，有利等位基因在种群中的频率增加。

Lamarck vs Darwin: Lamarck proposed inheritance of acquired characteristics (e.g., giraffes stretch their necks during life; offspring inherit longer necks). Darwin's mechanism is heritable genetic variation acted on by selection — traits must be genetically encoded to be inherited. Alberta Biology 20 B2.3k: "compare Lamarckian and Darwinian explanations of evolutionary change."拉马克 vs 达尔文：拉马克提出获得性性状遗传（如长颈鹿在生命中伸长脖子；后代遗传更长的脖子）。达尔文的机制是可遗传的遗传变异受自然选择作用——性状必须经遗传编码才能遗传。阿尔伯塔 Biology 20 B2.3k："比较拉马克与达尔文对进化变化的解释。"

• Variation:变异： differences in heritable traits among individuals in a population. Sources: (1) mutation — random changes in DNA sequence, the ultimate source of new alleles; (2) sexual reproduction — recombination and independent assortment shuffle existing alleles into new combinations. Without variation, natural selection cannot operate.种群中个体之间可遗传性状的差异。来源：(1) 突变——DNA 序列的随机改变，新等位基因的最终来源；(2) 有性生殖——重组与独立分配将现有等位基因洗牌成新组合。没有变异，自然选择无法运作。
• Adaptation:适应： a heritable trait that increases an organism's ability to survive and reproduce in its environment. Adaptations arise by natural selection acting on variation over many generations. Examples: camouflage coloring, antibiotic resistance in bacteria, the shape of a bird's beak.增加生物在其环境中存活和繁殖能力的可遗传性状。适应通过自然选择对变异作用经过多代而产生。例如：保护色、细菌的抗生素耐药性、鸟类喙的形状。
• Fitness:适合度： in evolutionary biology, fitness is specifically the relative reproductive success of an individual compared to other members of the population — not physical strength. An individual with high fitness passes more copies of its alleles to the next generation. Fitness is always measured relative to the environment: an allele that is adaptive in one environment may be neutral or harmful in another.在进化生物学中，适合度特指个体相对于种群其他成员的相对繁殖成功率——而非身体力量。适合度高的个体将更多等位基因拷贝传递给下一代。适合度始终相对于环境来衡量：在一种环境中适应的等位基因在另一种环境中可能是中性的或有害的。

Three modes of natural selection (shift in trait distribution): (1) Directional selection — one extreme phenotype is favoured (e.g., darker moths in sooty environments); allele frequency shifts continuously in one direction. (2) Stabilizing selection — intermediate phenotype is favoured; both extremes are selected against (e.g., human birth weight). (3) Disruptive selection — both extremes are favoured over the intermediate; can lead to two distinct phenotypic groups (potential driver of speciation).三种自然选择模式（性状分布的移动）：(1) 定向选择——有利于一个极端表现型（如煤烟环境中深色蛾）；等位基因频率持续向一个方向移动。(2) 稳定化选择——有利于中间表现型；两端极端均受选择压力（如人类出生体重）。(3) 分裂选择——两个极端均优于中间型；可产生两个截然不同的表现型群体（物种形成的潜在驱动力）。

• Mutation:突变： random changes in the DNA sequence. The ultimate source of all new alleles. Most mutations are neutral; some are harmful; a few are beneficial. Mutation rate alone is too slow to explain observed evolutionary change — selection and other mechanisms amplify rare mutations.DNA 序列的随机改变。所有新等位基因的最终来源。大多数突变是中性的；部分有害；少数有益。仅突变速率太慢，无法解释观测到的进化变化——选择与其他机制放大了罕见突变。
• Gene flow:基因流： movement of alleles between populations via immigration or emigration of individuals. Gene flow tends to reduce genetic differences between populations. If stopped (e.g., by a geographic barrier), isolated populations diverge over time.通过个体迁入或迁出在种群间移动等位基因。基因流倾向于减少种群间的遗传差异。若基因流受阻（如因地理屏障），孤立种群将随时间趋于分化。
• Genetic drift:基因漂变： random changes in allele frequency due to chance, not selection. Strongest in small populations. Two special cases: (1) Bottleneck effect — a catastrophic event drastically reduces population size; the survivors' allele frequencies may differ greatly from the original population; genetic diversity is reduced. (2) Founder effect — a small group colonizes a new area; the founders carry only a subset of the original alleles, establishing a new population with low diversity.由偶然性而非选择引起的等位基因频率随机变化。在小种群中效果最强。两种特殊情况：(1) 瓶颈效应——灾难性事件急剧减少种群规模；幸存者的等位基因频率可能与原始种群大相径庭；遗传多样性降低。(2) 建立者效应——少数个体开拓新区域；建立者仅携带原始等位基因的一个子集，建立多样性较低的新种群。
• Natural selection:自然选择： the only mechanism that consistently produces adaptive change. Acts on existing variation; cannot create new alleles. Changes allele frequencies directionally based on which traits improve survival and reproduction in the current environment.唯一能持续产生适应性变化的机制。作用于现有变异；不能创造新等位基因。根据哪些性状在当前环境中能提高存活和繁殖能力，定向地改变等位基因频率。

• Biological species concept:生物种概念： a species is a group of populations whose members can interbreed and produce fertile offspring, but cannot do so with members of other species (Ernst Mayr). Reproductive isolation is the defining criterion.物种是指其成员之间可以交配并产生可育后代，但不能与其他物种成员交配的种群集合（恩斯特·迈尔）。生殖隔离是定义性标准。
• Allopatric speciation:异域物种形成： a geographic barrier (mountain range, river, ocean) separates a population. The two isolated populations accumulate different mutations, experience different selection pressures, and experience genetic drift independently. Over time they diverge until they are reproductively isolated — two new species. This is the most common mode of speciation. Example: Galápagos finches diverged from a single mainland ancestor.地理屏障（山脉、河流、海洋）将一个种群分隔。两个孤立的种群积累不同的突变，经历不同的选择压力，并独立发生基因漂变。随时间推移它们趋于分化，直至生殖隔离——形成两个新物种。这是最常见的物种形成方式。示例：加拉帕戈斯雀从单一大陆祖先分化而来。
• Sympatric speciation:同域物种形成： speciation occurs within the same geographic area without physical isolation. Often driven by disruptive selection, polyploidy (in plants), or assortative mating. Less common than allopatric speciation.物种形成发生在同一地理区域内，无物理隔离。通常由分裂选择、多倍性（植物中）或选择性交配驱动。比异域物种形成少见。
• Reproductive isolating mechanisms:生殖隔离机制：
  • Prezygotic: prevent mating or fertilization — temporal isolation (different breeding seasons), behavioral isolation (different courtship displays), habitat isolation (different microhabitats), mechanical isolation (incompatible structures), gametic isolation (incompatible gametes).合子前：阻止交配或受精——时间隔离（不同繁殖季节）、行为隔离（不同求偶行为）、栖息地隔离（不同微生境）、机械隔离（不相容的结构）、配子隔离（不相容的配子）。
  • Postzygotic: hybrid offspring are produced but are inviable or infertile — hybrid inviability, hybrid infertility (e.g., mule from horse × donkey).合子后：产生杂交后代但不存活或不育——杂交不活力、杂交不育（如马与驴杂交产生骡）。

A population is in Hardy-Weinberg equilibrium (not evolving) if ALL five conditions are met: (1) very large population (no genetic drift); (2) random mating; (3) no mutation; (4) no gene flow (closed population); (5) no natural selection. Real populations violate at least one condition, so the H-W model identifies which mechanism is causing change by comparing observed frequencies to H-W expectations.当且仅当全部五个条件满足时，种群处于哈迪-温伯格平衡（不在进化）：(1) 种群极大（无基因漂变）；(2) 随机交配；(3) 无突变；(4) 无基因流（封闭种群）；(5) 无自然选择。真实种群至少违反一个条件，因此哈迪-温伯格模型通过将观测频率与哈迪-温伯格预期进行比较，来识别哪种机制正在引起变化。

The two equations (for a two-allele system, dominant allele $A$ with frequency $p$, recessive allele $a$ with frequency $q$):两个方程（对于两个等位基因体系，显性等位基因 $A$ 频率为 $p$，隐性等位基因 $a$ 频率为 $q$）：

• Divergent evolution:趋异进化： one ancestral species evolves into two or more different species as populations adapt to different environments. Produces homologous structures. Example: Darwin's finches, each adapted to a different food source on different islands.一个祖先物种进化为两个或多个不同物种，各种群适应不同环境。产生同源结构。示例：达尔文雀，各自在不同岛屿上适应不同食物来源。
• Convergent evolution:趋同进化： unrelated species evolve similar adaptations in response to similar environmental pressures. Produces analogous structures. Example: wings of birds, bats, and insects; streamlined body shape of dolphins and sharks.无亲缘关系的物种因相似的环境压力而独立演化出相似的适应性特征。产生同功结构。示例：鸟类、蝙蝠和昆虫的翅膀；海豚与鲨鱼的流线型体形。
• Adaptive radiation:适应辐射： a single ancestral species rapidly diversifies into many species, each filling a different ecological niche. Often follows a mass extinction event (removes competitors) or colonization of a new environment. Example: Galápagos finches; Australian marsupials after the dinosaur extinction.单一祖先物种迅速多样化为许多物种，各自占据不同的生态位。通常跟随大规模灭绝事件（清除竞争者）或进入新环境之后发生。示例：加拉帕戈斯雀；恐龙灭绝后的澳大利亚有袋类动物。
• Co-evolution:协同进化： two or more species evolve in response to each other. Each change in one species acts as a selection pressure on the other. Classic examples: flowering plants and their pollinators; host-parasite arms races; predator-prey cycles of adaptation.两个或多个物种相互响应而进化。一个物种的每次变化都成为对另一物种的选择压力。经典示例：开花植物与其传粉者；宿主-寄生物的军备竞赛；捕食者-猎物适应的循环。
• Extinction:灭绝： the permanent disappearance of a species. Environmental changes that exceed a species' ability to adapt lead to extinction. NGSS HS-LS4-5 states: "Evaluate the evidence supporting claims that changes in environmental conditions may result in (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species."物种的永久消失。超过物种适应能力的环境变化导致灭绝。NGSS HS-LS4-5 指出："评估支持以下主张的证据：环境条件变化可导致(1)某些物种个体数量增加；(2)新物种随时间出现；(3)其他物种灭绝。"