--- title: "Adapted to Their World" book: "Primary & Middle School Biology" subject: biology language: en chapter: 28 exercises: 11 source: https://one-course.com/books/biology/1/en/chapter/28-adapted-to-their-world --- # Chapter 28 — Adapted to Their World Put a polar bear in the Sahara and a camel on the pack ice, and neither would last a season. Yet each, at home, is a champion: the bear swims iced seas in comfort, the camel crosses deserts that would finish a horse in days. [Living things](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living) fit their worlds with an exactness that repays close study — feature by feature. ## 28.1 What adaptation means **Definition 28.1 (Adaptation).** An *adaptation* is a feature of a [living thing](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living)’s body or behavior that fits it to the conditions of its [environment](https://one-course.com/books/biology/1/en/chapter/13-caring-for-nature#def-g2-caring-for-nature-environment) — to the cold or the drought, to its food, to its hunters. [Proposition 11.4](https://one-course.com/books/biology/1/en/chapter/11-where-animals-live#prop-g2-where-animals-live-fit) showed [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) fitting their [habitats](https://one-course.com/books/biology/1/en/chapter/11-where-animals-live#def-g2-where-animals-live-habitat); adaptation is that fit, examined piece by piece. **Example 28.2 (The camel, piece by piece).** The desert’s problems: heat, no water, soft sand. The camel’s answers: humps of fat — a [food store](https://one-course.com/books/biology/1/en/chapter/20-animals-through-the-seasons#def-g3-animals-through-seasons-active) for lean crossings; the ability to drink a hundred litres in minutes and then go days without; wide two-toed feet that do not sink in sand; nostrils that close against blowing dust and long double eyelashes to match. Every desert problem, met by a feature. ![The desert specialist at work: wide feet on soft sand, a hump of reserves, and eyelashes built for dust.](https://one-course.com/images/onecourse/chapters/biology-1/g4-adapted-to-their-world/img-5652f75e4796.jpg) *The desert specialist at work: wide feet on soft sand, a hump of reserves, and eyelashes built for dust.* **Example 28.3 (The polar bear, piece by piece).** The pack ice’s problems: cold, icy water, prey that is hard to approach on white ice. The bear’s answers: thick [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) over a deep layer of fat — double insulation; broad, slightly webbed paws — snowshoes and paddles in one; white coat — invisible against the snow it hunts on. The same exactness, tuned to the opposite world. **Proposition 28.4 (Adaptations answer problems).** Wherever the [environment](https://one-course.com/books/biology/1/en/chapter/13-caring-for-nature#def-g2-caring-for-nature-environment) sets a hard problem, the [living things](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living) at home there carry features answering it: - cold: thick [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) , fat layers, small [ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) that lose little warmth; - drought: water storage, waxy [skins](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) , deep [roots](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) ; - life in water: streamlined bodies, fins and webbed feet, water-shedding coats; - hunters all around: camouflage colors, armor, [spines](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) , speed, and [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) set wide to watch all round; - hunting for a living: sharp senses, forward [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) , claws and speed ( [Proposition 10.4](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#prop-g2-what-animals-eat-match) ). **Proof.** *Admitted at this level.* ∎ ## 28.2 Plants are adapted too **Example 28.5 (The cactus).** The desert tests [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) hardest — they cannot walk to water. The cactus answers: a thick, barrel-shaped [stem](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) that stores water and does the [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts)’ light-catching work; [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) shrunk to [spines](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), losing almost no water — and defending the barrel against thirsty [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal); [roots](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) spread wide and shallow to catch a whole rare shower at once. **Example 28.6 (Alpine cushions).** High mountain [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) face freezing wind. Many grow as tight, ground-hugging cushions: inside the cushion, the wind is broken and the air stays milder — a shape that is shelter. Lowland cousins of the same [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) grow tall and loose; the mountain forms hug the rock. **Method 28.7 (Reading an organism’s world from its body).** Given an unfamiliar [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) or [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant): 1. list its striking features — coat, feet, [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) , body shape, [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) , [roots](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) ; 2. for each, ask: *what problem would this solve?* 3. assemble the answers into a picture of its home — cold or hot, wet or dry, hunter or hunted; 4. check the guess against where the organism really lives. This is [Method 11.6](https://one-course.com/books/biology/1/en/chapter/11-where-animals-live#met-g2-where-animals-live-matching) grown up: from matching a [habitat](https://one-course.com/books/biology/1/en/chapter/11-where-animals-live#def-g2-where-animals-live-habitat) to reconstructing a world. **Example 28.8 (The method on a mystery skin).** A museum drawer holds an unlabelled [skin](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense): dense soft [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering), tiny [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense), huge shovel-shaped front claws. [Fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) says mammal; the shovels say digging; the useless [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) say life in the dark. Verdict: an underground digger — and indeed it is a mole ([Example 11.5](https://one-course.com/books/biology/1/en/chapter/11-where-animals-live#ex-g2-where-animals-live-mole)), read correctly from three features alone. **Remark 28.9 (How does the fit come about?).** A camel never *decides* to grow wide feet, and no polar bear chooses its white coat. How, then, do [living things](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living) come to fit their worlds so well? It is one of [biology](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living)’s deepest questions, and its full answer — how the fit builds up, generation after generation — is a story this book keeps for a later year. For now, learn to *see* the fit: the seeing is what made the question askable. ## 28.3 Exercises **Exercise 28.1 ★.** What is an [adaptation](#def-g4-adapted-to-their-world-adaptation)? Give one [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) example and one [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) example. **Solution of Exercise 28.1.** A feature of body or behavior that fits a [living thing](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living) to its [environment](https://one-course.com/books/biology/1/en/chapter/13-caring-for-nature#def-g2-caring-for-nature-environment)’s conditions. [Animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal): the polar bear’s double insulation of [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) and fat. [Plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant): the cactus’s water-storing [stem](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts). **Exercise 28.2 ★.** Name three desert problems and the camel’s answer to each. **Solution of Exercise 28.2.** No water: drinking a hundred litres at once and lasting days without, plus the humps’ fat store. Soft sand: wide two-toed feet. Blowing dust: closable nostrils and long double eyelashes. (Heat and hunger: the humps again — fat for lean crossings.) **Exercise 28.3 ★.** Name three pack-ice problems and the polar bear’s answer to each. **Solution of Exercise 28.3.** Cold: thick [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) over a deep fat layer. Icy water and snow: broad, slightly webbed paws — snowshoes and paddles. Wary prey on white ice: the camouflage of a white coat. **Exercise 28.4 ★.** What jobs do the cactus’s [spines](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) do? What does its barrel [stem](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) store, and what work has the [stem](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) taken over? **Solution of Exercise 28.4.** The [spines](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton) are shrunken [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts): they lose almost no water and defend the [plant](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) against thirsty [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal). The barrel [stem](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) stores water, and has taken over the [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts)’ light-catching work. **Exercise 28.5 ★.** Why do many high-mountain [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) grow as tight cushions? **Solution of Exercise 28.5.** The cushion shape breaks the freezing wind: inside it the air stays milder. The shape itself is the shelter. **Exercise 28.6 ★.** Give two [adaptations](#def-g4-adapted-to-their-world-adaptation) of hunted [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) and two of hunters, from [Proposition 28.4](#prop-g4-adapted-to-their-world-answers). **Solution of Exercise 28.6.** Hunted: camouflage colors, armor or [spines](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-skeleton), speed, wide-set [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) watching all round (two suffice). Hunters: forward-facing [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense), sharp senses, claws, speed (two suffice). **Exercise 28.7 ★.** Retell [Example 28.8](#ex-g4-adapted-to-their-world-mystery): which three features gave the mole away, and what did each one say? **Solution of Exercise 28.7.** Dense soft [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) — a mammal; huge shovel-shaped front claws — a digger; tiny weak [eyes](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) — life in the dark. Together: an underground digging mammal, the mole. **Exercise 28.8 ★.** Try it: pick any [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) you can watch — a duck, a cat, a spider — and run [Method 28.7](#met-g4-adapted-to-their-world-read) on it: three features, three problems solved. **Solution of Exercise 28.8.** Open answer. Example for the duck: webbed feet (paddling), water-shedding [feathers](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) (staying dry and warm afloat), flat sifting beak (feeding from water). **Exercise 28.9 ★★.** The desert fox has enormous [ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense); the arctic fox, tiny ones. Using the cold line of [Proposition 28.4](#prop-g4-adapted-to-their-world-answers), explain both — what must big [ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) do with warmth? **Solution of Exercise 28.9.** [Ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) are radiators: big thin ones shed body warmth. In the desert, shedding warmth is the problem to solve — enormous [ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) cool the fox. On the ice, keeping warmth is everything — tiny [ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) lose the least. One organ, two climates, two opposite sizes. **Exercise 28.10 ★★.** A mystery [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal): streamlined body, webbed hind feet, dense water-shedding [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering), whiskers, and it holds its breath well. Reconstruct its world with [Method 28.7](#met-g4-adapted-to-their-world-read). (It builds dams.) **Solution of Exercise 28.10.** Streamlining, webbed feet and breath-holding say: a swimmer and diver; dense water-shedding [fur](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-covering) says: a mammal living half in cold water; whiskers say: feeling its way in dark or murky water. A water-dwelling, dam-building mammal of rivers and lakes — the beaver. **Exercise 28.11 ★★★.** The whale ([Example 14.5](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#ex-g3-sorting-living-things-surprises)) is a mammal shaped like a [fish](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups): streamlined, finned, smooth. The trout is a [fish](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) shaped the same way. What does this resemblance between two *unrelated* swimmers show about [adaptations](#def-g4-adapted-to-their-world-adaptation) — who set the shape, the family or the water? **Solution of Exercise 28.11.** The water set it. Whale and trout inherited nothing swimming-shaped from a shared family — one is a mammal, the other a [fish](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) — yet the same problem, moving fast through water, favors the same streamlined answer in both. [Adaptations](#def-g4-adapted-to-their-world-adaptation) answer the [environment](https://one-course.com/books/biology/1/en/chapter/13-caring-for-nature#def-g2-caring-for-nature-environment)’s problems; similar problems can draw similar shapes from very different families.