In plain English: HS-LS4-2 is the NGSS high school performance expectation that asks students to construct an evidence-based explanation of evolution from four factors: the potential of a species to increase in number, heritable variation from mutation and sexual reproduction, competition for limited resources, and the spread of individuals better able to survive and reproduce. It is usually taught in Biology.
Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment.
Clarification Statement: Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs and proportional reasoning.
Assessment Boundary: Assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution.
Next Generation Science Standards · Disciplinary Core Idea: Biological Evolution: Unity and Diversity · Official standard
Students build an explanation of how populations evolve by natural selection, one factor at a time, and back each factor with data. They compare how fast a population could grow with how fast it really grows, trace where heritable differences come from, identify what individuals compete for, and use survival data, simple distribution graphs and proportions to show which individuals leave more offspring. By the end they write explanations that connect all four factors to a change in a population.
The NGSS Clarification Statement says: "Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs and proportional reasoning." The Assessment Boundary says: "Assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution." Every scenario on this page is explained with the four factors only. All data sets are invented for teaching and labeled as invented; several are modeled on real studies, which are named only in general terms. Students do the practice of constructing explanations from evidence in every activity.
Learning Objectives
By the end of this lesson, students will be able to:
Use numbers to compare the potential growth of a population with its observed size and explain what the difference means
Explain how mutation and sexual reproduction produce heritable variation, and distinguish heritable traits from traits acquired during a lifetime
Identify the limited resource in a scenario and explain how competition for it affects which individuals survive
Use survival percentages, proportions and before-and-after distribution graphs as evidence that individuals with some traits leave more offspring
Construct a written explanation that connects all four factors to a change in a population
Prior Knowledge Required
Students should already be comfortable with:
How genetic variation can raise some individuals' chances of surviving and reproducing MS-LS4-4
Using simple math to show how natural selection changes traits over time MS-LS4-6
Genes, alleles and the idea that mutations change DNA MS-LS3-1
Meiosis and fertilization as the steps of sexual reproduction
Write two numbers on the board: "A pair of field mice can raise about 20 young in one season." and "The number of mice in this field has stayed about the same for 10 years."
Warm-Up Prompt
"Both statements are true. If each pair raises 20 young, where do the extra mice go? Which young do you think are most likely to be the ones that survive, and why?"
Record answers in two columns, "what limits the mice" and "which ones survive". The first column becomes competition for limited resources; the second becomes variation and differential survival. Leave both columns up for the closure.
Direct Instruction15-20 minutes
The four factors. (1) Every species can produce far more offspring than survive. (2) Individuals differ in heritable traits, because mutations create new versions of genes and sexual reproduction shuffles existing versions into new combinations. (3) Resources such as food, water, space and light are limited, so individuals compete and many die before reproducing. (4) Individuals whose heritable traits help them survive and reproduce leave more offspring, so those traits become more common in the next generation. Evolution is the result: a change in the traits of the population, not of any one individual. Present one example per factor, then one that uses all four.
Factor 1: potential to increase
A pair of field mice raises about 20 young in a season, and half are female (invented round numbers). Suppose every young mouse survived and each new pair did the same.
Result: Each generation multiplies by 20 ÷ 2 = 10: 2, 20, 200, 2,000, 20,000 mice after four generations. The real field population stays near the same size, so on average only 2 of every 20 young (10%) survive to breed.
Factor 2: heritable variation
A human sex cell receives one chromosome from each of 23 pairs. A mutation in a pigment gene in a cell that makes eggs or sperm can change the hair color of offspring.
Result: Independent assortment alone gives 223 = 8,388,608 possible chromosome combinations per parent, and two parents give about 7 × 1013 combinations, before crossing over adds more. Mutations add new versions of genes; sexual reproduction mixes them. Only changes in sex cells are inherited.
Factor 3: competition for limited resources
About 1,000 oak seedlings sprout in a sunny forest gap (invented count). Ten years later about 40 saplings remain.
Result: Only 40 ÷ 1,000 = 4% survive. Light, water and soil nutrients in the gap are limited, and seedlings that grow faster shade out slower neighbors. If growth rate is partly heritable, the survivors pass on faster growth.
Factor 4: proliferation of better survivors (proportional reasoning)
On ground blackened by a fire, birds eat 30 of 100 pale grasshoppers and 10 of 100 dark ones in a season (invented). Color is heritable, and every survivor leaves the same number of offspring.
Result: Survivors: 70 pale and 90 dark. The dark share rises from 100 ÷ 200 = 50% to 90 ÷ 160 = 56.25%, about 56%, in one generation. Dark grasshoppers are not getting darker; more of the next generation comes from dark parents.
All four factors: antibiotic resistance
Bacteria in a nutrient broth at body temperature can double about every 30 minutes. For illustration, suppose about 1 cell in 10 million carries a mutation that makes it resistant to an antibiotic.
Result: From one cell, 20 doublings (10 hours) give 220 = 1,048,576 cells (factor 1). A population of 1 billion cells would include about 100 resistant cells (factor 2; bacteria also swap genes, which is beyond this standard). The antibiotic kills susceptible cells, and the survivors compete for the nutrients left (factor 3). Resistant cells multiply and soon make up nearly all of the population (factor 4).
After each example, ask: "Which number is the evidence, and which factor does it support?" Stress two points: variation must exist before the environment changes (the antibiotic does not create the mutation), and "better able to survive" always depends on the environment (dark color helps on burned ground and hurts on pale sand).
Guided Practice15 minutes
Pairs analyze invented data modeled on long-term studies of seed-eating finches on a small island. During a drought, small soft seeds ran out and mostly large, hard seeds remained. Beak depth is strongly heritable. Diagram 1 graphs the same data.
Guided practice data: beak depth of 200 finches before a drought and the 46 that survived it (invented)
Beak depth class (mm)
Birds before
Survivors
8.0
10
1
8.5
26
3
9.0
44
7
9.5
50
11
10.0
42
12
10.5
20
8
11.0
8
4
Total
200
46
Compute the percent that survived in each class. What pattern do you see as beak depth increases?
The mean beak depth before the drought was 9.45 mm. Compute the mean for the survivors and compare.
Name the limited resource and explain why deeper beaks helped birds compete for it.
Predict the mean beak depth of the survivors' offspring compared with the population before the drought, and explain which factor makes your prediction possible.
Write a four-sentence explanation, one sentence per factor, using at least two numbers from the table.
Expected results: survival rises from 10% in the 8.0 mm class to 50% in the 11.0 mm class, and the survivors' mean is about 9.76 mm. Because beak depth is heritable, the next generation's mean should be larger than 9.45 mm.
Independent Practice15-20 minutes
Each student writes a claim, evidence and reasoning explanation from the data card below. The explanation must name all four factors and use at least two numbers.
Data card: cold tolerance in an invented lizard population (a real cold snap in Texas in 2014 produced a similar result in green anole lizards)
Measurement
Value
Lizards measured in the fall
120
Mean lowest temperature at which a lizard can still turn itself over
10.8 °C
Lizards alive after an unusually cold winter
34
Mean for the survivors
9.1 °C
Eggs laid by a female in one season
about 10
Breeding tests
cold tolerance is partly heritable
Students should compute the survival rate (34 ÷ 120, about 28%) and explain why a lower value means a hardier lizard. Ask: "What is the limited resource here, if it is not food?" (warm shelter sites, and the energy to survive cold nights).
Closure5 minutes
Exit ticket: give each student one card describing a scenario with one factor missing (for example, a population with no variation in color facing a new predator). Students name the missing factor and explain why evolution of that trait cannot happen without it. Return to the warm-up columns and label them with factors 3 and 4.
Differentiation Strategies
For Struggling Students
Provide a four-row organizer (factor, what it means, evidence from the data, sentence) to fill in before writing a full explanation
Use whole-number data sets first, such as 100 of each type, so percents can be read directly from counts
Give color-coded cards for the four factors and have students match each card to a sentence in a model explanation
For Advanced Students
Ask students to explain why the survivors' offspring might not reach the survivors' mean beak depth if beak depth is only partly heritable
Have students design a follow-up study that would show whether a change in a trait is heritable or only a response to the environment
Ask students to write a two-generation spreadsheet model for the grasshopper example and find the survival difference needed to reach 75% dark in five generations
Assessment Guidance
What to Look For
Look for explanations that name all four factors and tie each to evidence: a growth number for factor 1, a source of variation for factor 2, a named limited resource for factor 3, and a survival or reproduction difference for factor 4. Watch for students who say individuals change because they need to, who treat traits acquired during life as inherited, or who describe the environment as causing the mutation. Strong answers make clear that the population changes because some individuals leave more offspring.
02
Classroom Activities
3 Activities
1
Paper Dot Predators
25 minGroups of 4
Groups model a population of 40 insects using paper dots in four colors on a brown patterned cloth. Students act as birds and pick up dots with forceps. Survivors reproduce, and the cloth can hold only 40 dots, so the model includes all four factors.
Procedure
Scatter 10 tan, 10 brown, 10 green and 10 white dots on the cloth. One student is the "birds"; the others keep time and record.
The bird picks up dots one at a time with forceps, looking away between picks, until 20 dots have been eaten. The 20 left are the survivors.
Each survivor reproduces: add one dot of the same color for each survivor, bringing the population back to 40, the most the cloth can hold.
Repeat for three generations and record the counts. Rotate the bird role each round.
Mutation card: in generation 2, the teacher may give one group a single new color (orange). Groups track whether it spreads.
Sample Data (invented)
Survivors after each round (tan, brown, green, white): generation 1: 7, 8, 4, 1; generation 2: 8, 9, 3, 0; generation 3: 8, 10, 2, 0. After reproduction the populations are 14, 16, 8, 2, then 16, 18, 6, 0, then 16, 20, 4, 0.
Discussion Questions
In the sample data, brown dots increased in every generation, from 10 to 20. Which factor explains why?
White dots disappeared by generation 2. What would have to happen for white dots to return, and which factor is that?
The cloth holds only 40 dots. Which factor does that rule stand for, and what would happen to the colors if the cloth could hold 1,000?
What part of real evolution does this model leave out or oversimplify?
Modification for Distance Learning
Students use a photo of a patterned surface with colored dots added digitally, click to remove the first 20 they notice, and record the survivors in a shared spreadsheet.
2
Beak Tools and Limited Seeds
25 minGroups of 4-5
Each student is a bird with a heritable "beak": kitchen tongs, a binder clip or a plastic spoon. Birds collect food from a shared tray for 30 seconds per round. Birds that gather too little food "die", and survivors pass their beak type to offspring.
Procedure
Fill a paper tray with 60 dried beans and 60 lentils. Each bird drops food into its own cup (its "stomach").
Round 1 (wet year): 30 seconds of feeding. Any bird with fewer than 10 items dies. Each survivor adds one offspring with the same beak type from the reserve students.
Round 2 (drought): remove all lentils, leaving only 60 beans, and repeat.
Round 3: the drought continues. Record the number of each beak type after every round.
Safety: food items are not eaten; check for legume allergies and use paper tokens instead if needed.
Discussion Questions
What was the limited resource, and how did the drought change it?
Which beak type became more common after the drought? Use your counts.
If every bird had the same beak, could the population's beaks change over the rounds? Which factor would be missing?
Challenge Variation
Give one reserve student a new beak type (clothespin) as a "mutation" in round 2. Groups predict whether it will spread and test the prediction.
3
Explanation Workshop: Rock Pocket Mice
25 minGroups of 3
Groups use a set of evidence cards to write a four-factor explanation of why most rock pocket mice living on dark lava flows in the southwestern United States have dark fur, while most on nearby pale rock have sandy fur. Then groups trade and critique each other's explanations.
Evidence Cards
Card 1 (real): owls and other predators hunt pocket mice mainly by sight at night.
Card 2 (real): in some lava-flow populations, dark fur is caused by mutations in a single pigment gene; mice with and without the mutation are otherwise alike.
Card 3 (invented): in a survey of 100 mice on a lava flow, 85 were dark; on pale rock 10 km away, 5 of 100 were dark.
Card 4 (invented): in a release study, owls caught 22 of 50 light mice and 6 of 50 dark mice on lava in one season.
Card 5 (real): female pocket mice can have more than one litter a year, with a few young per litter.
Task
Compute the survival percent of each color on lava from Card 4.
Write one paragraph that uses every card and names every factor.
Trade paragraphs with another group. Mark each factor you find, and write one question about a claim that lacks evidence.
Discussion Questions
On lava, dark mice survived at a higher rate than light mice (88% compared with 56%). Which factor does this number support?
The mutation for dark fur may have arisen before the mice lived on lava. Why does that matter for the explanation?
Would the same trait be an advantage on pale rock? What does that tell you about the phrase "better able to survive"?
Modification for Distance Learning
Post the cards as images in a shared slide. Groups write in breakout rooms and leave critique comments on another group's slide.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Beak Depth Before and After a Drought
The guided practice data (invented, modeled on studies of seed-eating finches), drawn to scale as the percent of each group in each beak-depth class. The survivors' distribution sits further to the right than the original population's, because a larger share of deep-beaked birds survived when only large, hard seeds were left.
Diagram 2: Potential Growth and Observed Size of a Beetle Population
Invented data, drawn to scale. If every beetle survived, a population of 50 that doubles each generation would reach 3,200 after six generations (dashed line). The observed population (solid line) levels off near 150, because food and space are limited and most offspring die before breeding.
04
Homework Assignment
~30 min
HS-LS4-2 Homework: Building Four-Factor Explanations
Directions: All data sets are invented for practice unless a fact is marked real. Show every calculation, and name the factor (1-4) that each piece of evidence supports.
Part 1: Growth and Variation (Problems 1-2)
A female frog lays about 2,000 eggs in a season. (a) Suppose every egg survived, half became females, and each female laid 2,000 eggs the next season. How many eggs would the second generation of females lay in total? (b) The frog population of the pond stays about the same from year to year. If a female lays 2,000 eggs in her lifetime and, on average, 2 of them survive to breed, what percent survive? (c) Which factor do these numbers illustrate?
Fruit flies have 4 pairs of chromosomes (real). (a) How many different chromosome combinations can one fly produce in its eggs or sperm by independent assortment alone? (b) Name one other process that makes offspring even more varied, and one process that creates new versions of genes. (c) A fly loses a wing tip in an accident. Explain why this change will not show up in its offspring.
Part 2: Competition and Survival Data (Problems 3-4)
After a cold, wet spring killed most flying insects for a week, a colony of 300 swallows (body mass 20-30 g) was weighed before the storm, and the 90 survivors were counted by mass class. Before: 20-22 g, 60 birds; 23-25 g, 150 birds; 26-28 g, 90 birds. Survivors: 6, 45 and 39. (a) Compute the percent that survived in each class. (b) Sketch a before-and-after distribution graph. (c) Name the limited resource and explain why heavier birds may have had an advantage in competing for survival.
A field has 10,000 weeds, of which 100 carry a heritable mutation for herbicide resistance. A spray kills 99% of the non-resistant weeds and 5% of the resistant ones. (a) How many of each type survive? (b) What percent of the survivors are resistant, to the nearest whole percent? (c) Explain which factors the numbers support, and why the farmer should expect the spray to work less well next year.
Part 3: Explanations from Evidence (Problems 5-6)
A textbook from 1900 says: "Giraffes stretched their necks to reach high leaves, and their offspring were born with longer necks." (a) Identify the error. (b) Rewrite the explanation using all four factors. (c) Describe one piece of evidence that would support your version.
In a town that began spraying an insecticide, mosquitoes were tested each year with the same dose. The percent surviving the test was 2% in year 1, 8% in year 2, 25% in year 3, 60% in year 4 and 85% in year 5. (a) By how many percentage points did survival change from year 1 to year 5? (b) Describe the shape of the change. (c) Write an explanation of the trend that names all four factors and cites at least two of the data points.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Percents, proportions and totals correct with work shown
Method correct with one arithmetic error
Four Factors
Every factor named and linked to specific evidence
Two or three factors named, or factors named without evidence
Heritability
Distinguishes inherited variation from traits acquired in a lifetime
Implies acquired traits or needs cause change in one place
Explanation Quality
Claim, evidence and reasoning are clear and connected
Claim present but reasoning is incomplete
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented for practice unless marked real. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which observation best shows the first factor, the potential for a species to increase in number?
Answer: C
Producing far more offspring than are needed to replace the parents is the potential to increase. Choice A is the observed outcome, which shows that most offspring die. Choice B is variation (factor 2), and choice D is competition (factor 3).
Question 2 of 20 · Multiple Choice
An invented population of 30 insects doubles each generation with no deaths. How many insects will there be after 5 generations?
Answer: D
30 × 25 = 30 × 32 = 960. Choice A adds 30 five times (linear growth) instead of doubling. Choice B stops after 4 generations, and choice C goes to 6 generations.
Question 3 of 20 · Multiple Choice
Which change could be passed on to offspring and add to heritable variation?
Answer: A
Only changes to DNA in cells that make eggs or sperm can be inherited. Choices B, C and D are acquired during a lifetime and do not change the DNA passed to offspring; the belief that they are inherited is a well-known error.
Question 4 of 20 · Multiple Choice
How does sexual reproduction add to variation in a population?
Answer: B
Meiosis (independent assortment and crossing over) and the joining of two sex cells produce new combinations of existing gene versions. Choice A describes mutation, the other source of variation. Choice D is false, since no individual chooses traits for its offspring.
Question 5 of 20 · Multiple Choice
An organism has 3 pairs of chromosomes. How many chromosome combinations can its sex cells have from independent assortment alone?
Answer: C
Each pair can go two ways, so there are 23 = 8 combinations. Choice B multiplies 2 × 3, and choice D squares 3; neither follows the two-choices-per-pair rule.
Question 6 of 20 · Multiple Choice
Which scenario is an example of competition for a limited resource among members of one species?
Answer: B
The swifts compete for a limited resource (nest sites), and the outcome decides who reproduces. Choice A is predation, which is a cause of death but not competition among members of the same species. Choices C and D do not involve a shared, limited resource.
Question 7 of 20 · Multiple Choice
Birds eat 40% of 200 light beetles and 15% of 200 dark beetles on dark soil (invented). If every survivor leaves the same number of offspring, what percent of the next generation will be dark, to the nearest tenth?
Answer: B
Survivors: light 200 × 0.60 = 120, dark 200 × 0.85 = 170. Dark share = 170 ÷ 290 = 58.6%. Choice A ignores the difference in survival. Choice D is the light share, and choice C is the percent of dark beetles eaten.
Question 8 of 20 · Multiple Choice
In evolutionary terms, which individual is "better able to survive and reproduce"?
Answer: D
What counts is the number of offspring that survive to pass the traits on, and it depends on the environment. Choices A and C describe size or aggression, which can help or hurt. Choice B is not enough: a long-lived individual with no offspring passes on nothing.
Question 9 of 20 · Multiple Choice
Before a flood, the mean body length of fish in a stream was 42 mm. The survivors of the flood had a mean length of 45 mm, with a similar spread. Which conclusion do these data best support?
Answer: B
A shift in the mean of the survivors means larger fish survived at a higher rate. Choice A confuses a change in which fish remain with growth of individuals. Choice C goes beyond the data, since a similar spread means some short fish survived. Choice D wrongly has the environment creating mutations.
Question 10 of 20 · Multiple Choice
A student writes: "Polar bears turned white because they needed to hide in the snow." Which revision is a correct explanation?
Answer: C
Choice C includes existing heritable variation, a survival and reproduction advantage, and change across generations. Choices A and D describe changes within one lifetime, and choice B has the environment causing mutations instead of selecting among existing variation.
Question 11 of 20 · Multiple Choice
Head lice in a school became harder to kill with a common lice shampoo after several years of use. Which explanation fits the evidence best?
Answer: A
Resistance was present as heritable variation before treatment; the shampoo removed susceptible lice, and survivors left the offspring. Choices B and C describe learned or acquired resistance, which is not inherited. Choice D ignores the evidence that the lice changed.
Question 12 of 20 · Multiple Choice
Which scenario includes all four factors needed for evolution by natural selection?
Answer: B
Choice B has many offspring (factor 1), heritable variation (2), a limited resource (3) and differential survival and reproduction (4). Choice A lacks variation. Choice C lacks competition. Choice D describes one individual responding, not a population changing across generations.
Question 13 of 20 · Multiple Choice
A pair of songbirds raises 10 chicks during its lifetime, and the population stays about the same size year after year. On average, how many of the 10 chicks survive to breed?
Answer: A
In a stable population each pair is replaced, on average, by one surviving pair: 2 of 10 chicks, or 20%. Choice D assumes every chick survives, which would make the population grow fivefold each generation. Choice C is the number that die, not the number that survive.
Question 14 of 20 · Multiple Choice
After a windstorm on an island, researchers compared a histogram of wing length for all flies before the storm with a histogram for the survivors. Which result would support the claim that shorter-winged flies were better able to survive?
Answer: C
If shorter-winged flies survived at a higher rate, a larger share of the survivors falls in the short classes, so the distribution shifts left. Choice A would show no advantage, choice B the opposite advantage, and choice D is impossible because survivors are a subset of the original flies.
Question 15 of 20 · Short Answer
One bacterium is placed in a nutrient broth where it divides every 20 minutes (about the fastest rate for common gut bacteria). How many cells would there be after 3 hours if none died? Why can this growth never continue for long?
3 hours = 180 minutes = 9 doublings, so 29 = 512 cells. The growth stops because nutrients and space in the broth are limited (factor 3), so cells compete and most eventually cannot divide.
Question 16 of 20 · Short Answer
Explain the difference between mutation and sexual reproduction as sources of heritable variation. Give one example of each.
Mutation changes the DNA sequence and can create a new version of a gene, for example a base change in a pigment gene that gives dark fur. Sexual reproduction does not create new versions; it shuffles existing ones into new combinations through independent assortment, crossing over and fertilization, so siblings differ from each other and from their parents.
Question 17 of 20 · Short Answer
In a drying pond, 120 fast-developing tadpoles and 180 slow-developing tadpoles compete for limited algae. Before the pond dries, 60 fast and 27 slow tadpoles reach the frog stage (invented). Compute each survival percent and the percent of the new frogs that were fast developers. Which factors do the data support?
Fast: 60 ÷ 120 = 50%. Slow: 27 ÷ 180 = 15%. Fast developers make up 60 ÷ 87 = 69% of the new frogs, compared with 40% of the tadpoles. The data support competition for limited resources (food and time) and the proliferation of better survivors, if developmental speed is heritable.
Question 18 of 20 · Short Answer
In an invented moth population, 30% are dark. In a smoky year, 80% of dark moths and 50% of light moths survive. What percent of the survivors are dark, to the nearest tenth of a percent?
Out of 100 moths: dark survivors 30 × 0.80 = 24, light survivors 70 × 0.50 = 35. Dark share = 24 ÷ 59 = 40.7%, up from 30%.
Question 19 of 20 · Short Answer
A large predatory fish is stocked in a lake. Twenty generations later, most of the small minnows in the lake are faster swimmers than minnows in a nearby lake without the predator. Explain this change using all four factors.
Model answer: (1) Minnows produce far more young than the lake can support. (2) Swimming speed varies among minnows and is partly heritable, because of mutations and the mixing of genes in sexual reproduction. (3) Minnows compete for limited food and hiding places, and the predator eats those it can catch. (4) Faster minnows escape more often, live to reproduce and leave more offspring, so fast swimming becomes more common each generation. Full credit needs all four factors and a clear link to the predator.
Question 20 of 20 · Short Answer
Before and after a hurricane, an invented lizard population was counted by body length: small, 40 before and 10 after; medium, 100 and 40; large, 60 and 30. Compute the survival percent for each class and state what the data suggest.
Small: 10 ÷ 40 = 25%. Medium: 40 ÷ 100 = 40%. Large: 30 ÷ 60 = 50%. Survival rises with body length, so larger lizards were better able to survive the storm; if body length is heritable, the next generation should include a larger share of large lizards.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS4-2 mean?
HS-LS4-2 asks students to explain, with evidence, that evolution results mainly from four factors: species can produce more offspring than survive, individuals vary in heritable traits, resources are limited, and individuals better able to survive and reproduce leave more offspring. The code means High School, Life Science, core idea 4 (Biological Evolution: Unity and Diversity), performance expectation 2.
What are the four factors of evolution in HS-LS4-2?
They are (1) the potential for a species to increase in number, (2) heritable genetic variation from mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of organisms better able to survive and reproduce. Together they describe natural selection. Students should be able to point to evidence for each one in a real or invented case.
What is the assessment boundary for HS-LS4-2?
The official Assessment Boundary says assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution. Those ideas are beyond this standard. Lessons should explain changes with the four factors and choose examples where those four are the main story.
Is HS-LS4-2 taught in Biology?
Yes. It is usually taught in high school Biology in the evolution unit, after students have learned how DNA and meiosis produce variation (HS-LS3-1 and HS-LS3-2). It pairs closely with HS-LS4-3 and HS-LS4-4, which use statistics and adaptation to extend the same ideas.
Where does genetic variation come from?
New versions of genes come from mutations, changes in the DNA sequence. Sexual reproduction then reshuffles existing versions through independent assortment, crossing over and the joining of two sex cells. Only variation in DNA passed to offspring matters for evolution; injuries, exercise and suntans are not inherited.
Why don't populations keep growing if organisms have so many offspring?
Because resources such as food, water, space and light are limited. Most offspring die before they reproduce, from starvation, predators, disease or harsh weather. In a population that stays the same size, each pair is replaced on average by just two offspring that survive to breed.
Do individual organisms evolve?
No. Individuals can grow, learn or acclimate, but their inherited DNA does not change to fit their surroundings. Evolution is a change in the traits of a population over generations, which happens because some individuals leave more offspring than others.
What kind of evidence do students use for HS-LS4-2?
The Clarification Statement names mathematical models such as simple distribution graphs and proportional reasoning. Students compare histograms of a trait before and after an event, compute survival percents for each type, compare potential growth with observed population size, and use proportions to predict the makeup of the next generation.
Is natural selection the same thing as evolution?
Not quite. Evolution is the change in heritable traits of a population over generations; natural selection is the process described by the four factors that causes much of that change. Other processes also cause evolution, but they are beyond this standard.
How is HS-LS4-2 different from HS-LS4-4?
HS-LS4-2 focuses on the four factors that drive evolution and on evidence for each one. HS-LS4-4 focuses on the result, how natural selection leads to populations that are adapted to their environment. Many teachers teach them together, with HS-LS4-2 first.
07
Related Standards
6 standards
These standards connect to HS-LS4-2: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS4-4Prerequisite
Explain how genetic variation raises some individuals' chances to survive and reproduce
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