Adaptation and an Introduction to Evolution
FoundationAdaptation is the fit between a living thing and its environment — cactus needles and polar-bear white coats; evolution explains how such traits formed over ages: variation arises in a population, the environment through natural selection keeps those better able to survive, and helpful traits pass to offspring. Antibiotic resistance shows evolution happening before our eyes, and protecting habitats preserves diversity.
- Adaptation is a survival feature fitting the environment — cactus needles, polar-bear white, streamlined fish.
- Darwin's Galapagos finches inspired natural selection: variation, competition, survival of the fitter, inheritance.
- Fossils are evidence: horses' small many-toed ancestors, whales' transitional land-stage fossils.
文體小知識：生物科普說明文用生動例子和比喻解釋生命現象的原理，把抽象的科學概念講得具體易明。
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1Look closely at living things and each shows features fitted to its environment: the desert cactus turns its leaves into needles to cut water loss and stores water in its stem; the polar bear's white coat camouflages it in snow while thick fat keeps it warm; fish have streamlined bodies with fins and tails for swimming; the chameleon changes colour to merge with its background. Features that help a living thing survive and breed in a particular environment are called adaptations.
2How do adaptations arise? In the nineteenth century Darwin sailed round the world on HMS Beagle and noticed on the Galapagos Islands that finches on different islands had different beaks — some thick for cracking seeds, some slim for picking insects. He proposed natural selection: individuals of a species vary; food and space are limited, so they compete; individuals with more helpful variations survive and breed more easily, passing traits to offspring; over long ages populations change until new species may form. Fossils support this: horses' ancestors were dog-sized and many-toed, evolving into the large single-hoofed modern horse; transitional fossils show whales returning to the sea from land mammals.
3Evolution is not only ancient history: bacteria screened by antibiotics survive if resistant, then multiply until drugs weaken — natural selection before our eyes; in industrial England the peppered moth's dark form grew common because soot-blackened trunks hid it from birds. These show: change the environment, and the direction of selection changes.
4Understanding evolution teaches protection: when environments change fast — forests felled, climate shifting — species may not adapt in time and slide toward extinction; protecting habitats and populations preserves the diversity built over ages of evolution. And like all science, the theory of evolution rests on masses of evidence and keeps being refined with new discoveries — that is the strength of science.
1Summary 重點摘要
Adaptation is the fit between a living thing and its environment — cactus needles and polar-bear white coats; evolution explains how such traits formed over ages: variation arises in a population, the environment through natural selection keeps those better able to survive, and helpful traits pass to offspring. Antibiotic resistance shows evolution happening before our eyes, and protecting habitats preserves diversity.
2Vocabulary cards Vocabulary
A feature that helps a living thing survive and breed in its environment.
The process by which populations change over ages, forming new species.
The mechanism by which the environment keeps individuals better able to survive and breed.
The differences among individuals of a species, the raw material of selection.
A group of living things that can interbreed and produce young.
The remains or traces of ancient life preserved in rock, evidence of evolution.
The environment where a living thing lives and finds food.
Colouring or shape that hides a creature in its setting, like the polar bear's white coat.
The survival and spread of bacteria that withstand antibiotics, weakening the drugs.
The death of every individual of a species, gone from Earth forever.
3Step by step Steps
- Step 1: Spot adaptationsAdaptation means the forms and habits of a living thing fit its environment, helping it feed, escape enemies and breed. Example: the cactus's needle leaves cut water loss and its fleshy stem stores water, fitting the desert; the water lily's broad leaves lie flat on the water to catch more sun. Reading features for their function is the first step in studying life; the polar bear's white coat and thick fat, and the fish's streamlined body, follow the same logic.
- Step 2: See variation everywhereEven within one species, individuals differ; these differences are variation, the raw material of evolution. Example: bean plants of one kind grow tall or short with pods long or short; classmates differ in height too. Most variation comes from the shuffling of genetic material, can be passed on, and gives a population its diversity; without variation, natural selection would have nothing to choose.
- Step 3: Learn the four beats of natural selectionNatural selection runs in four beats: individuals vary, the environment tests, the fittest survive, and the traits pass on. Example: in a finch flock, thick-beaked birds crack hard seeds; in a drought the small seeds vanish, only thick beaks eat well and breed, and the next generation has more thick beaks. The environment acts like a sieve, keeping the better-fitted traits; Darwin's watching of finch beaks on the Galapagos Islands began exactly here.
- Step 4: Read fossil evidenceFossils are traces of ancient life; lined up by age, they show how living things changed through time. Example: arrange horse fossils by age and the body grows larger while four toes become one, matching the shift from forest to grassland — a film played out over tens of millions of years; transitional fossils of whales returning from land to sea support the theory just as clearly.
- Step 5: Watch evolution nowEvolution is not only ancient history; it happens before our eyes, and drug resistance in bacteria is a clear example. Example: doctors tell patients to finish the whole antibiotic course precisely so the more resistant bacteria left behind do not multiply and weaken the drug. Stopping early helps resistant bacteria pass the test, making treatment harder and harder; this shows natural selection at work at this very moment.
- Step 6: Analyse change and the direction of selectionWhen the environment changes, the direction of natural selection changes too, and once-advantaged traits may turn into handicaps. Example: in the Industrial Revolution soot blackened trunks, so dark peppered moths evaded birds and rose in number; when pollution eased, the trunks lightened and pale ones increased again. One species, opposite fortunes — all depending on the environment; when change comes too fast, species may fail to adapt and slide toward extinction.
- Step 7: Link to conservationEvery species is the outcome of long evolution; once its habitat disappears, the species can hardly survive. Example: a frog lives only in one wetland; fill it in and the frog has nowhere to go — protecting habitats preserves the diversity evolution has built. Conservation is not merely kindness to animals but guarding the planet's library of life; keeping populations and their habitats intact preserves what ages of evolution have accumulated.
4Diagrams Diagrams
5Worked example Example
Example: a farmer has used the same insecticide for ten years and finds it weaker every year. Explain with natural selection and give two suggestions.
- Explanation: variation exists in the pest population — some insects naturally tolerate the chemical more; each spraying acts as a screening that removes the susceptible ones.
- Process: the susceptible die, the tolerant survive and breed, passing tolerance to their offspring; after ten rounds the population is mostly tolerant, and the drug weakens year by year.
- Suggestion one: rotate insecticides of different ingredients so pests cannot adapt to several screens at once, slowing the build-up of resistance.
- Suggestion two: adopt integrated pest management — natural enemies, crop rotation and weed clearance — to rely less on one chemical and curb the pests as a whole.
- Answer: Repeating one insecticide keeps screening for tolerant individuals until the population is mainly tolerant and the drug fades; rotating chemicals of different kinds and practising integrated control slow that selection and keep the protection working for the long run.
6Common mistakes Mistakes
7Quick check Quick check
Q1What is adaptation? Give one example.
Q2What are the key points of natural selection?
Q3What did Darwin observe on the Galapagos Islands?
Q4Why does misusing antibiotics weaken the drugs?
Q5Why is protecting habitats linked to evolutionary diversity?
8Recap Recap
- Adaptation is a survival feature fitting the environment — cactus needles, polar-bear white, streamlined fish.
- Darwin's Galapagos finches inspired natural selection: variation, competition, survival of the fitter, inheritance.
- Fossils are evidence: horses' small many-toed ancestors, whales' transitional land-stage fossils.
- Antibiotic resistance and the peppered moth show evolution happening now — change the setting, change the selection.
- Protecting habitats buys time to adapt, preserving diversity built over ages.