Overview

Lesson Procedure

65-70 minutes of class time across 5 phases.

1. Warm-Up10 minutes
2. Direct Instruction20 minutes
3. Guided Practice15 minutes
4. Independent Practice15-20 minutes
5. Closure5 minutes

1. Warm-Up10 minutes

   Warm-Up Prompt

   "Write down the first picture that comes to mind for the phrase 'the struggle for existence.' Then name two living things that could win that struggle without fighting anything."

   Give students three minutes, then list their pictures on one side of the board and their non-fighting winners on the other. Read the first Darwin excerpt aloud while students follow on paper; the paragraphs are numbered in the margin, and the marks [...] show where lines were left out. Ask them to circle each number Darwin gives in paragraphs 1 and 2, and, in paragraph 3, to underline each living thing Darwin names and write beside it what it depends on.

   1A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase. Every being, which during its natural lifetime produces several eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise, on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for in this case there can be no artificial increase of food, and no prudential restraint from marriage. Although some species may be now increasing, more or less rapidly, in numbers, all cannot do so, for the world would not hold them.

   2There is no exception to the rule that every organic being naturally increases at so high a rate, that if not destroyed, the earth would soon be covered by the progeny of a single pair. Even slow-breeding man has doubled in twenty-five years, and at this rate, in a few thousand years, there would literally not be standing room for his progeny. Linnæus has calculated that if an annual plant produced only two seeds—and there is no plant so unproductive as this—and their seedlings next year produced two, and so on, then in twenty years there would be a million plants.

   [...]

   3I am tempted to give one more instance showing how plants and animals, most remote in the scale of nature, are bound together by a web of complex relations. [...] I have, also, reason to believe that humble-bees are indispensable to the fertilisation of the heartsease (Viola tricolor), for other bees do not visit this flower. From experiments which I have tried, I have found that the visits of bees, if not indispensable, are at least highly beneficial to the fertilisation of our clovers; but humble-bees alone visit the common red clover (Trifolium pratense), as other bees cannot reach the nectar. Hence I have very little doubt, that if the whole genus of humble-bees became extinct or very rare in England, the heartsease and red clover would become very rare, or wholly disappear. The number of humble-bees in any district depends in a great degree on the number of field-mice, which destroy their combs and nests; and Mr. H. Newman, who has long attended to the habits of humble-bees, believes that “more than two thirds of them are thus destroyed all over England.” Now the number of mice is largely dependent, as every one knows, on the number of cats; and Mr. Newman says, “Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice.” Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!

2. Direct Instruction20 minutes

   Present what the 11-12 standard adds to the 9-10 version. The organization must do more than connect and distinguish ideas: each new element builds on that which precedes it, so that later sections would not make sense without earlier ones (Diagram 1). Development must be thorough, with the most significant details rather than all relevant ones. Writers vary syntax as well as transitions. And part d names metaphor, simile and analogy as tools for managing a complex topic, which means the writer must also know where each comparison stops being accurate. Work through the five examples below, then read the model text.

   • Introducing a complex topic

     Flat opening: Darwin had many important ideas about nature. It names a person but not a concept, and it gives the reader no reason to keep reading.

     Result: Revision: Darwin's phrase "struggle for existence" is widely quoted and often misread, because readers take literally a term he meant as a metaphor.

   • Building each element on the one before

     Two facts presented side by side: A female bullfrog can lay thousands of eggs in a season. A pond's frog population stays about the same from year to year.

     Result: Linked so that the second idea depends on the first: A female bullfrog can lay thousands of eggs in a season, yet the frog population of a pond stays about the same from year to year; it follows that nearly all of those eggs never become breeding adults.

   • Analogy with its limit

     Concept: geometrical increase, the growth of a population that multiplies by the same factor each generation.

     Result: Analogy: geometrical increase works like a savings account with compound interest, where each year's growth is added to the total and the next year's growth is figured on the larger total. Limit: money needs no food or space, while a real population soon runs out of both.

   • Varied syntax

     Three sentences with the same pattern: Seeds fall on crowded ground. Seedlings compete for light. Most seedlings die.

     Result: Revision: When seeds fall on ground that other plants already cover, the seedlings compete for light, and most of them die. The survivors are few.

   • Precise language and the conventions of biology

     Draft sentence: The moths turned dark because they wanted to hide from birds. It gives the moths an intention and treats a population change as a choice.

     Result: Revision: In woods darkened by soot, birds caught pale moths more often than dark ones, so dark moths left more offspring and became more common over many generations.

   Hand out the model text. On the first reading, students mark the sentence in paragraph 1 that previews the three steps. On the second, they draw an arrow from the first sentence of each body paragraph back to the idea it depends on, and they bracket every comparison (metaphor, simile or analogy). Point out the conventions of science writing the model follows: the source and date named once, technical terms explained in plain words, processes described as outcomes rather than intentions, and quotations kept short and exact. Close with the conclusion, which states an implication of the concept ("articulating implications or the significance of the topic," in the words of part f) instead of summarizing it.

   1The phrase "struggle for existence" calls up pictures of combat: stags locking antlers, wolves fighting over a carcass. Charles Darwin, who placed the phrase at the center of On the Origin of Species in 1859, meant something far broader, and most of what he meant involves no fighting at all. Grasping his meaning takes three steps, each resting on the one before: what Darwin included in the term, why he thought the struggle could never stop, and what the struggle decides.

   2A Deliberately Wide Term
   Darwin stretches the term well beyond open conflict, and one of his most famous examples involves no fight at all. In England, he reports, "humble-bees alone visit the common red clover," so the clover's seed crop depends on these bumblebees. The bees depend in turn on the number of field mice, "which destroy their combs and nests," and the mice on the number of local cats. A district with many cats may therefore have more clover. None of these animals fights the clover, yet each one helps to decide whether it leaves seed. To struggle, in Darwin's sense, is to depend on other living things and to succeed or fail at leaving offspring, not only to fight.

   3Why the Struggle Never Ends
   Once the term covers survival and reproduction alike, Darwin can claim that the struggle "inevitably follows from the high rate at which all organic beings tend to increase." The reasoning is arithmetic. A population that multiplies in each generation grows geometrically: it doubles, doubles again, and keeps doubling. Darwin borrows an example from the Swedish naturalist Linnaeus, in which an annual plant that left only two seeds each year would have a million descendants within twenty years. No habitat could hold them. The struggle, in other words, is not an occasional crisis but a permanent condition, because "more individuals are produced than can possibly survive."

   4What the Struggle Decides
   If most offspring die young, the question becomes which ones survive to reproduce. An analogy helps here. Imagine a lottery in which every seedling holds a ticket and only a few tickets win the chance to flower. A seedling that tolerates shade a little better holds, in effect, a second ticket. In a single season the extra ticket rarely matters; over thousands of generations it tips the outcome again and again, and the trait spreads. This is the step at which the struggle for existence becomes the engine of natural selection.

   5Where the Words Can Mislead
   The lottery also shows what the word struggle hides: in a lottery no one fights, and in most of Darwin's cases no one does either. Words such as struggle and battle can suggest that organisms try to change or that nature chooses a winner. Biology writing today avoids that impression. It describes outcomes rather than intentions, and it measures success by the number of offspring an organism leaves, not by its strength.

   6Darwin's phrase has lasted for more than a century and a half because it is vivid, but it is useful only when read as he defined it. Understood broadly, the struggle for existence names the fact on which his theory rests: in every generation more living things begin life than can complete it, and small inherited differences decide which of them leave descendants. The same reasoning now guides work far from Darwin's own garden, for example in medicine, where bacteria that survive an antibiotic pass their resistance on to the next generation.

3. Guided Practice15 minutes

   Pairs complete the table below. For each comparison, they write what it helps a reader understand and what it could lead a reader to believe that is not true. Then the class compares answers for the last column, which has no single right answer.

   Testing the comparisons in Darwin's excerpt and the model text

   Comparison	Where it appears	Type	What it clarifies (students fill in)	What it could distort (students fill in)
   "struggle for existence"	Darwin, paragraph 1	Metaphor
   A lottery with a few winning tickets	Model text, paragraph 4	Analogy
   "the engine of natural selection"	Model text, paragraph 4	Metaphor
   A savings account with compound interest	Direct Instruction, example 3	Analogy

   Next, pairs read the weak draft below and list its problems under four headings: organization and unity, accuracy and selection, syntax and transitions, and style. They do not rewrite it yet; that happens in Activity 3.

   Charles Darwin sailed on a ship called the Beagle and visited the Galapagos Islands, where he saw lots of finches and giant tortoises. Survival of the fittest means the strongest animals win the fight. Animals fight. Plants fight too. They fight for food. They fight for water. Basically everything is trying to kill everything else, which is kind of brutal. Also Darwin says it's like a tree, which makes sense because trees are in nature. So in conclusion, nature is one big battle and only the strong survive.

4. Independent Practice15-20 minutes

   Students read the second Darwin excerpt, in which he compares the relationships among species to "a great tree," and plan the explanation they will write for homework. Readers: adults who read a general science magazine, who have heard of evolution but have never read Darwin. Each student (1) underlines every phrase in which Darwin says one part of the tree "may represent" something; (2) chooses the three details they consider most significant for these readers and writes one sentence justifying each choice; and (3) sketches the order of their sections so that each depends on the one before. The two animals Darwin names are the platypus (Ornithorhynchus) and a South American lungfish (Lepidosiren).

   1The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.

5. Closure5 minutes

   Exit ticket: (1) Write the question your homework's second section will answer, and explain why it cannot come first. (2) Write one sentence that shows where Darwin's tree simile stops being accurate. (3) Name one implication of the tree simile that your conclusion could state.

   Teacher note on the sources: Darwin's words are printed exactly as in the 1859 first edition, including older spellings ("fertilisation," "connexion," "favoured"), "humble-bees" for bumblebees, and his use of "man" for human beings, which was standard at the time. His phrases "tried to branch out" and "tried to overmaster" are figurative; biologists today avoid wording that gives species intentions, and the lesson treats this as one of the limits of his comparisons. Natural selection, the idea these passages lead to, remains a central, well-supported explanation in biology; modern science has added what Darwin could not know, such as how traits are inherited, and has revised some of his details. The lesson teaches how to explain a scientific concept clearly and accurately, as a science text would; students are not asked to state personal beliefs about it. The first excerpt comes from later pages of Chapter III than the excerpt on the RST.11-12.1 page, so the two lessons do not repeat a passage.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   A student's assignment is to explain what Darwin meant by "struggle for existence." Which thesis statement fits an informative/explanatory text?

   ADarwin's phrase is misleading, and scientists should stop using it in textbooks. BDarwin used the phrase in a broad sense that includes dependence and reproduction, not only fighting. CWhen I first heard the phrase, I pictured animals fighting in the jungle at night. DDarwin was the greatest scientist of his century, and this phrase proves it.

2. Question 2 of 20 · Multiple Choice

   How does paragraph 1 of the model text introduce its topic?

   AIt gives the date and title of Darwin's book and then summarizes the whole book. BIt defines natural selection before it mentions the struggle for existence. CIt starts from the common picture of combat, says Darwin meant more, and previews three steps. DIt lists Darwin's four examples in the order in which he gives them.

3. Question 3 of 20 · Multiple Choice

   Why does the model place the lottery analogy (paragraph 4) after the section on why the struggle never ends (paragraph 3)?

   ABecause the lottery explains what happens to the surplus of offspring that paragraph 3 shows must exist BBecause analogies should always come near the end of an explanatory text CBecause paragraph 3 contains no quotations and paragraph 4 needed to follow one that did DBecause the lottery analogy is less important than the rest of the text

4. Question 4 of 20 · Multiple Choice

   Which sentence, added to the end of paragraph 3 of the model text, would most weaken the unity of the explanation?

   AA sentence noting that most plants leave far more than two seeds, so the real rate is faster still BA sentence explaining that doubling twenty times gives just over a million CA sentence adding that animals multiply geometrically too, not only plants DA sentence adding that Linnaeus also created the system of naming species with two Latin words

5. Question 5 of 20 · Multiple Choice

   A writer wants to show readers the chain of dependence in paragraph 3 of the first Darwin excerpt, which runs from cats to field mice to humble-bees to red clover. Which format would aid comprehension most?

   AA graph of how fast a population of plants grows over twenty years BA flow diagram with an arrow for each link in the chain, each labeled with its effect CA color photograph of a field of red clover in flower in summer DA short video clip of a cat catching a field mouse in a barn

6. Question 6 of 20 · Multiple Choice

   A writer wants to point out that Darwin's cat-to-clover chain in paragraph 3 of the first excerpt is a reasoned inference rather than something he measured. Which quotation is most significant for that point?

   A"The number of humble-bees in any district depends in a great degree on the number of field-mice" B"humble-bees alone visit the common red clover (Trifolium pratense), as other bees cannot reach the nectar" C"Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine ... the frequency of certain flowers" D"Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere"

7. Question 7 of 20 · Multiple Choice

   A writer wants to show readers that geometrical increase applies even to living things that breed slowly. Which detail from the first Darwin excerpt is most significant for that point?

   ADarwin's statement that even slow-breeding humans have doubled their numbers in twenty-five years BDarwin's report that humble-bees alone visit the common red clover, since other bees cannot reach the nectar CDarwin's report that field-mice destroy the combs and nests of humble-bees in every district DDarwin's remark that plants and animals are bound together by a web of complex relations

8. Question 8 of 20 · Multiple Choice

   The readers of an explanation are biology students who already know what natural selection is. How should the writer adjust the explanation of the struggle for existence?

   AAdd a longer definition of natural selection at the start, since definitions are always helpful BSpend less space defining natural selection and more on how Darwin's broad sense differs from the everyday one CRemove all quotations from Darwin, since biology students do not need a source DReplace the technical terms with everyday words throughout the text

9. Question 9 of 20 · Multiple Choice

   In paragraph 3 of the model text, what does the sentence "The struggle, in other words, is not an occasional crisis but a permanent condition" do?

   AIt introduces a new example of geometrical increase that the paragraph has not yet discussed. BIt concedes that Darwin's reasoning in this part of the excerpt has a weakness. CIt begins the conclusion of the whole text by summing up all of the sections. DIt restates the arithmetic in general terms, and its "not ... but" structure sharpens the point.

10. Question 10 of 20 · Multiple Choice

    Which revision varies the syntax to show how these ideas relate? Rabbits breed quickly. Foxes eat rabbits. The rabbit population stays about the same.

    ARabbits breed quickly, and foxes eat rabbits, and the rabbit population stays about the same. BRabbits breed quickly. Foxes eat rabbits. So the rabbit population stays about the same. CAlthough rabbits breed quickly, their population stays about the same, because foxes eat many of them. DRabbits breed quickly; foxes eat rabbits; the rabbit population stays about the same.

11. Question 11 of 20 · Multiple Choice

    Choose the transition that best clarifies the relationship: In every generation more offspring are produced than can survive; ____, small inherited differences decide which individuals leave descendants.

    Aconsequently Bfor instance Cnevertheless Dmeanwhile

12. Question 12 of 20 · Multiple Choice

    In paragraph 3 of the first Darwin excerpt, Darwin says that plants and animals "are bound together by a web of complex relations." What does the web metaphor help a reader understand?

    AThat animals build structures to catch their food, as spiders spin webs BThat each species is linked to many others, so a change in one can spread along the links to species far away CThat species are caught in nature as flies are caught in a web, unable to escape or change DThat the only relation between two species is that one of them eats the other

13. Question 13 of 20 · Multiple Choice

    In the tree passage, Darwin writes, "I believe this simile largely speaks the truth." What does the word "largely" signal?

    AThat the simile applies only to large species such as trees and elephants BThat Darwin thinks the simile is entirely accurate in every detail CThat the simile was invented by Darwin rather than by earlier writers DThat the comparison holds in its main outline but not necessarily in every detail

14. Question 14 of 20 · Multiple Choice

    Which sentence best follows the conventions of biology writing?

    ALizards with longer legs escaped predators more often and left more offspring, so long legs became more common. BThe lizards tried to grow longer legs so that they could run away from their predators. CNature wanted faster lizards, so it chose the ones with the longest legs to survive. DThe weak, short-legged lizards were losers that deserved to be eaten by predators.

15. Question 15 of 20 · Short Answer

    Write an extended definition of natural selection for readers of a general magazine, three or four sentences long. Connect it to Darwin's struggle for existence, quote the first Darwin excerpt once, and include one thing natural selection is not.

    Show model answer

16. Question 16 of 20 · Short Answer

    Explain how paragraph 2 of the first Darwin excerpt builds on paragraph 1. Quote each paragraph once.

    Show model answer

17. Question 17 of 20 · Short Answer

    Revise this sentence from the weak draft so that it keeps a formal style and an objective tone and is accurate to Darwin's meaning: "Basically everything is trying to kill everything else, which is kind of brutal."

    Show model answer

18. Question 18 of 20 · Short Answer

    The weak draft ends, "So in conclusion, nature is one big battle and only the strong survive." Write a new concluding statement of two or three sentences that follows from an accurate explanation of the struggle for existence and states its significance in your own words, without repeating the model text's conclusion.

    Show model answer

19. Question 19 of 20 · Short Answer

    Combine these sentences from the weak draft into one or two sentences with varied structure, and correct the idea so that it matches Darwin's broad sense: "Animals fight. Plants fight too. They fight for food. They fight for water."

    Show model answer

20. Question 20 of 20 · Short Answer

    Darwin says the struggle follows "on the principle of geometrical increase." Write an analogy that explains geometrical increase to a general reader, using a comparison that does not appear in this lesson, and state one way the analogy breaks down.

    Show model answer

These standards connect to W.11-12.2: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.