HS-LS4-4: How Natural Selection Leads to Adaptation
In plain English: HS-LS4-4 is the NGSS high school performance expectation that asks students to construct an explanation, based on evidence, for how natural selection leads to adaptation of populations. Students use data on traits and allele frequencies to show how a difference in the environment changes who survives and reproduces, so the population shifts over generations. It is usually taught in Biology.
Construct an explanation based on evidence for how natural selection leads to adaptation of populations.
Clarification Statement: Emphasis is on using data to provide evidence for how specific biotic and abiotic differences in ecosystems (such as ranges of seasonal temperature, long-term climate change, acidity, light, geographic barriers, or evolution of other organisms) contribute to a change in gene frequency over time, leading to adaptation of populations.
Next Generation Science Standards · Disciplinary Core Idea: Biological Evolution: Unity and Diversity · Official standard
Students build explanations for how natural selection makes a population better suited to its environment over many generations. The explanation has four links: individuals vary in a trait, the variation is at least partly heritable, the environment makes some variants more likely to survive and reproduce, and so the alleles behind those variants become more common in the next generation. Students calculate allele and trait frequencies, compare populations living under different conditions, and use the numbers as evidence. Individuals do not adapt during their lives; populations adapt across generations.
The NGSS Clarification Statement says: "Emphasis is on using data to provide evidence for how specific biotic and abiotic differences in ecosystems (such as ranges of seasonal temperature, long-term climate change, acidity, light, geographic barriers, or evolution of other organisms) contribute to a change in gene frequency over time, leading to adaptation of populations." NGSS lists no Assessment Boundary for HS-LS4-4, so this lesson keeps the focus that statement sets. Each case on the page is tied to one kind of environmental difference: light and background color, long-term climate change, acidity, the evolution of other organisms, geographic barriers and seasonal temperature ranges. The cases are patterned on published studies, but every data set is invented for teaching and labeled that way. Students do the practice of constructing an explanation: they state a claim, cite data and reason with the steps of natural selection.
Learning Objectives
By the end of this lesson, students will be able to:
Calculate allele and trait frequencies from counts and describe how they change between populations or over generations
Identify the environmental difference (abiotic or biotic) that makes one variant more likely to survive and reproduce
Construct a claim, evidence and reasoning explanation that links variation, heritability, differential survival and reproduction, and a change in gene frequency
Distinguish adaptation of a population from changes in one individual, and correct explanations based on need or effort
Judge whether data show a heritable difference, for example by comparing offspring raised under the same conditions
Prior Knowledge Required
Students should already be comfortable with:
Genetic variation of traits and how it can raise the chance of surviving and reproducing MS-LS4-4
Using simple math to show how natural selection changes traits in a population MS-LS4-6
Genes, alleles and how mutations can change traits MS-LS3-1
Calculating fractions, decimals and percents from counts
Show two photos side by side: a dark pocket mouse on black lava rock and a sandy-colored mouse of the same species on pale desert sand, a few kilometers apart.
Warm-Up Prompt
"These mice belong to one species. Most mice on the lava are dark, and most mice on the sand are light. Write down how you think this happened. Then write one piece of data that would convince a skeptic your explanation is right."
Collect answers without correcting them. Sort them on the board into explanations about individuals changing ("the mice turned dark to hide") and explanations about which mice survived and had offspring. Tell students the lesson will test both kinds against data.
Direct Instruction15-20 minutes
The four links of natural selection. (1) Individuals in a population vary in a trait. (2) Some of that variation is heritable: it is caused by alleles that parents pass on. (3) The environment makes some variants more likely to survive and reproduce than others. (4) Those variants leave more offspring, so their alleles make up a larger share of the next generation. Repeated over many generations, the population becomes better suited to its environment: that is adaptation. Allele frequency is the share of all copies of a gene in the population that are one allele. In a sample of N individuals there are 2N copies, so the frequency of allele D is (2 x number of DD + number of Dd) / 2N. Work through the examples below, one kind of environmental difference at a time.
Light and background color (predation)
Invented sample of 60 rock pocket mice on dark lava: 22 DD, 26 Dd, 12 dd, where the dominant allele D gives dark fur. A sample of 60 on nearby light sand: 1 DD, 8 Dd, 51 dd. Owls and hawks hunt by sight.
Result: Lava: D = (2 x 22 + 26) / 120 = 70/120 = 0.58, and 48 of 60 mice (0.80) are dark. Sand: D = (2 x 1 + 8) / 120 = 10/120 = 0.08, and 9 of 60 (0.15) are dark. The allele that makes mice harder to see is common where it matches the rock.
Long-term climate change (snow cover)
Tawny owls come in a heritable grey form and brown form. Invented banding data: in a snowy winter, 120 of 150 grey owls and 32 of 50 brown owls survived; in a mild winter with little snow, 117 of 150 grey and 38 of 50 brown survived.
Result: Snowy winter: grey 0.80, brown 0.64, so selection strongly favors grey. Mild winter: grey 0.78, brown 0.76, almost no difference. As winters with deep snow become rarer, selection against brown owls weakens and the brown form can become more common.
Acidity (a common-garden test)
Frogs of one species breed in acidic bog ponds (pH about 4.5) and in neutral ponds (pH about 7). Invented lab data: 200 embryos from each kind of pond are raised in the same water at pH 4.2 and at pH 6.5.
Result: At pH 4.2: 156/200 = 0.78 of acid-pond embryos hatch, but only 84/200 = 0.42 of neutral-pond embryos. At pH 6.5: 184/200 = 0.92 and 188/200 = 0.94. Raised in the same water, the populations still differ, so acid tolerance is heritable and has been favored in the acidic ponds.
Evolution of other organisms (prey toxin)
Some newts carry a strong nerve toxin, and garter snakes that eat them can carry a resistance allele. Invented samples of 50 snakes each: where toxic newts live, 64 of 100 gene copies carry resistance; where there are no toxic newts, 2 of 100 do.
Result: Resistance allele frequency: 64/100 = 0.64 versus 2/100 = 0.02. Snakes without resistance that eat a toxic newt can be paralyzed or die, so resistance is favored only where the prey is toxic. As the newts evolve stronger toxin, selection on the snakes continues.
Seasonal temperature range (an enzyme allele)
Killifish live in salt marshes along the Atlantic coast. One allele of a gene for a metabolic enzyme works better in warm water. Invented frequencies of this warm-type allele at five sites are plotted in Diagram 2.
Result: Frequency falls from 0.95 in Florida (23 °C) to 0.06 in Maine (9 °C), dropping at every step to a colder site. The pattern follows temperature, which supports the claim that each version of the enzyme is favored where it works best.
After each example, ask the same three questions: "What varies? What in the environment differs? Which number shows the population has shifted?" Then show Diagram 1, a model of a mouse population on a new lava flow, to show that selection works over generations and that a stronger survival difference produces faster change.
Guided Practice15 minutes
Pairs analyze invented data patterned on studies of the medium ground finch on a Galapagos island. During a long drought, the small soft seeds ran out, and birds were left with large, hard seeds that only deep beaks can crack. Researchers measured beak depth in 200 banded birds before the drought and recorded which birds survived it.
Guided practice data (invented): beak depth of 200 finches before a drought
Beak depth (mm)
Birds before drought
Survivors
8.0-8.9
60
9
9.0-9.9
80
22
10.0-10.9
45
21
11.0-11.9
15
8
Find the survival rate in each beak class. (0.15, 0.275, 0.47 and 0.53: survival rises with beak depth.)
Use the class midpoints (8.5, 9.5, 10.5, 11.5 mm) to estimate the mean beak depth before the drought and among survivors. (About 9.58 mm and 9.97 mm, a shift of about 0.4 mm.)
The offspring of the survivors, measured as adults, have a mean beak depth of about 9.9 mm. What does this add to the evidence? (Beak depth is heritable, so the shift carried into the next generation.)
Write a claim, evidence and reasoning explanation that uses all four links of natural selection and at least two numbers from the table.
Independent Practice10-15 minutes
Each student explains a new invented data set. Marine threespine stickleback have many bony armor plates. After the fish in a lake in Alaska were removed and marine stickleback recolonized it, researchers tracked the frequency of an allele for low armor. One explanation they tested: building armor uses energy and minerals that are scarce in fresh water, so low-armor fish grow faster and breed sooner in a lake.
Independent practice data (invented): low-armor allele in a lake population
Years after recolonization
0
4
8
12
Low-armor allele frequency
0.10
0.28
0.51
0.71
Students calculate the change in each 4-year interval (0.18, 0.23, 0.20), then write a claim, evidence and reasoning paragraph. Ask them to name one more measurement that would test the explanation, such as the growth rates of low-armor and full-armor fish raised in lake water.
Closure5 minutes
Exit ticket: "A classmate says: 'Each finch grew a deeper beak during the drought because it needed to crack hard seeds.' In three sentences, explain what is wrong and what actually changed." Look for: beak depth of an adult bird does not change to meet a need; birds that already had deeper beaks survived and bred more; the next generation had a higher mean because beak depth is inherited. Return to the warm-up sorting and ask which kind of explanation the data supported.
Differentiation Strategies
For Struggling Students
Give a four-box explanation frame with the headings Variation, Inheritance, Selection and Result, and have students fill one box per data set before writing a paragraph
Provide the allele count step as a table (2 x homozygous + heterozygous) so students only divide at the end
Start with the bead simulation before the data tables, so the numbers describe something students have seen happen
For Advanced Students
Show the model behind Diagram 1: with D dominant, the next generation's frequency is p' = p / (1 - s q2). Have students run it in a spreadsheet and find how long D takes to pass 0.5 for several values of s
Ask students why the warm-type allele in Diagram 2 does not reach 0 or 1 at every site, and how gene flow between neighboring marshes could keep the cline smooth
Have students write a rebuttal to a classmate who says the bead simulation proves that real mice evolved, naming what the model leaves out
Assessment Guidance
What to Look For
Strong explanations name the environmental difference, the trait that varies, why the trait is heritable, how survival or reproduction differs, and the change in frequency, with numbers from the data. Watch for explanations in which the organism "needs" or "tries" to change, in which individuals change their genes, or in which a mutation appears because of the environment. Check that students calculate allele frequency out of 2N alleles, not N individuals, and that they ask whether a difference is heritable before calling it an adaptation.
02
Classroom Activities
3 Activities
1
Bead Predators: Camouflage on Two Backgrounds
25 minGroups of 3-4
Groups model selection by predators. Paper dots (or dry beans) in a dark and a light color are scattered on a fabric sheet, and a "predator" picks up as many as possible with forceps in 20 seconds. Survivors each "reproduce" one offspring of the same color, and the group records the dark fraction for three generations on a dark sheet and on a light sheet.
Procedure
Start each sheet with 50 dark and 50 light dots, well mixed and scattered.
The predator picks up dots one at a time with forceps, eyes open, for 20 seconds or until 50 dots are taken. Keep taking turns as predator.
Count the survivors of each color, then add one dot of the same color for each survivor, so the population is back to 100.
Record the dark fraction for generations 0-3 and graph both sheets on one set of axes.
Safety: dry beans are not eaten, and spilled beans are picked up at once so nobody slips.
Sample Data (invented)
Dark sheet: predators took 36 light and 14 dark dots in round 1, 22 light and 28 dark in round 2, and 10 light and 40 dark in round 3. The dark fraction went 0.50, 0.72, 0.88, 0.96. Light sheet: predators took 34 dark and 16 light, then 24 dark and 26 light, then 12 dark and 38 light. The dark fraction went 0.50, 0.32, 0.16, 0.08.
Discussion Questions
On each sheet, the color that matched the background made up a larger share after every round. What in the model plays the role of heritable variation, and what plays the role of selection?
In round 3 on the dark sheet, predators took more dark dots (40) than light dots (10), yet the dark fraction still rose. How can both be true?
What does the model leave out that real mice have (mutation, mates, alleles instead of whole colors)? How would each change the result?
Modification for Distance Learning
Students scatter 50 dark and 50 light paper squares on a patterned rug or towel at home, have a family member act as predator, and post their table and graph to the class board.
2
Acid Ponds: Analyzing a Common-Garden Experiment
20 minPairs
Pairs analyze invented data from an experiment in which frog embryos from three acidic ponds and three neutral ponds were all raised in the same lab water at pH 4.2. They decide whether the data show a heritable difference, and explain how it arose.
Data (invented)
Embryos hatching out of 100 in each clutch set. Acidic ponds (field pH 4.4, 4.6, 4.8): 81, 74, 70. Neutral ponds (field pH 6.8, 7.0, 7.2): 45, 38, 40. In a control at pH 6.5, all six groups hatched between 90 and 95 out of 100.
Tasks
Find the mean hatching rate for each kind of pond at pH 4.2. (75 and 41 out of 100.)
Explain why raising every embryo in the same water is the key feature of the design.
Write a claim, evidence and reasoning explanation of how the acid-pond populations became tolerant.
Discussion Questions
Among the acid-pond groups, hatching at pH 4.2 is highest for the pond with the lowest field pH. Does that pattern support or weaken your explanation?
Why does the pH 6.5 control matter before you call the acid-pond embryos "better"?
Challenge Variation
Pairs design a follow-up: what would they measure in tadpoles from each pond to find out whether acid tolerance has a cost in neutral water?
3
Evidence Stations: Four Environments, Four Adaptations
25 minGroups of 3-4
Four stations each show one invented data set tied to a different environmental difference. At each station, groups calculate one number and write an explanation card that names the environmental difference, the trait, the evidence of change and the link to survival or reproduction. Groups rotate every 6 minutes.
Station Data (invented)
Station 1, soapberry bugs and a new host plant (evolution of other organisms): bugs feed by piercing fruit to reach seeds. On native vines with fruit about 11 mm deep, mean beak length is 9.3 mm. On an introduced tree with flat pods about 3 mm deep, bugs collected 50 years later have a mean beak length of 7.1 mm.
Station 2, lizards on islands separated by open water (geographic barrier): lizards moved to an island with only thin bushes have mean hind-leg length 26.6 mm after 12 years, compared with 28.5 mm on the source island with broad tree trunks.
Station 3, fruit flies in an orchard (seasonal temperature range): an allele linked to cold tolerance had a frequency of 0.62 in flies collected in spring, the offspring of winter survivors, and 0.48 in flies collected in late fall, after about 10 summer generations. The same swing was seen in each of three years.
Station 4, fish and predators in two streams: in a stream with large predatory fish, 58 of 80 guppies checked were mature at under 50 days old. Above a waterfall with no large predators, 21 of 80 were.
Discussion Questions
Stations 1 and 2 both show a trait that got smaller. Explain why getting smaller is still adaptation.
At Station 3 the allele frequency rises and falls every year. Explain how selection in winter and in summer could cause the swing, and why flies can adapt within one year at all.
At Station 4, what share of guppies matured early in each stream? (0.725 and 0.2625.) Why might early breeding be favored where adults are often eaten?
Modification for Distance Learning
Post each station as a slide with its data. Students submit four explanation cards through the class learning platform and comment on one classmate's card.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Model of Selection on a New Lava Flow
A model, not measured data. A mouse population colonizes a new dark lava flow with the dark allele D (dominant) at a frequency of 0.05. Light mice (dd) survive to breed 20% less often than dark mice (s = 0.20, blue) or 5% less often (s = 0.05, dashed navy). With s = 0.20, D passes 0.5 after 18 generations; with s = 0.05 it is still below 0.4 after 60. Curves computed with p' = p / (1 - s q2).
Diagram 2: A Warm-Type Enzyme Allele along a Coast
Invented frequencies of a warm-type allele of a metabolic enzyme gene in killifish at five salt-marsh sites, plotted against the site's mean annual water temperature. The allele is common in warm southern marshes and rare in cold northern ones, a pattern that follows temperature.
04
Homework Assignment
~30 min
HS-LS4-4 Homework: Explaining Adaptation with Data
Directions: Every data set is invented for practice but patterned on real studies. Show each calculation, and end every problem with a claim, evidence and reasoning explanation that uses the four links of natural selection: variation, inheritance, selection and the result over generations.
Part 1: Allele and Trait Frequencies (Problems 1-2)
Deer mice live on pale sand hills and on nearby dark farm soil. An allele L gives lighter fur. On the sand hills, a sample of 80 mice has 45 LL, 26 Ll and 9 ll. On dark soil, a sample of 80 has 3 LL, 18 Ll and 59 ll. (a) Find the frequency of L in each sample. (b) Explain the difference, naming the environmental difference and the selective agent. (c) Describe one experiment that would test your explanation directly.
Lizards in one area were measured for cold tolerance (the lowest temperature at which they can still turn over). Before an unusually cold winter the mean was 11.2 °C; the survivors averaged 9.6 °C. Offspring of the survivors, hatched and raised in a warm lab, averaged 10.0 °C. (a) Find the change from before the winter to the survivors and to the lab-raised offspring. (b) Explain why the lab-raised offspring are the key evidence. (c) Explain why the offspring mean did not drop all the way to 9.6 °C.
Part 2: Tracking Change over Generations (Problems 3-4)
In one region, the share of peppered moths that are dark was 0.90 in 1960, 0.80 in 1970, 0.62 in 1980, 0.35 in 1990 and 0.12 in 2000, after clean-air laws cut soot and pale lichens grew back on tree trunks. (a) Find the change in each decade and say which decade had the largest drop. (b) Explain the trend with natural selection. (c) Name one other explanation (such as moths moving in from other regions) and the data that would test it.
A model population of beetles on dark bark starts with 400 light beetles and 100 dark beetles. Each generation, birds eat 50% of the light beetles and 20% of the dark beetles, and then every survivor leaves two offspring of its own color (the parents die). (a) Find the dark fraction at the start and after 1 and 2 generations. (b) Explain why the fraction keeps rising even though the environment does not change. (c) Predict what happens if the bark turns light and the survival rates swap.
Part 3: Building and Critiquing Explanations (Problems 5-6)
Snowshoe hares turn white in fall and brown in spring; the timing is inherited. Where snow now arrives later, a hare that turns white early sits white on brown ground. In an invented study, mismatched hares survived each week with probability 0.93 and matched hares with 0.97. (a) Find the chance of surviving a 6-week mismatch period for each. (b) A student writes: "Hares will start changing color later because they need to stay hidden." Rewrite this as an explanation based on natural selection. (c) What would you measure over many generations to test it?
Mosquitofish live in isolated ponds on one island; the ponds are not connected, so fish cannot move between them. In 4 ponds with predatory fish, the mean escape speeds of adult mosquitofish were 58, 61, 60 and 57 cm/s. In 4 ponds without predators they were 48, 50, 47 and 51 cm/s. (a) Find the mean for each group of ponds. (b) Construct an explanation for the difference, including why the isolation of the ponds matters. (c) Design a test to show whether the difference is heritable.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Calculations
Frequencies, changes and means correct with the right denominator (2N for alleles)
Method correct with one error, or alleles counted out of N
Evidence
Explanation cites specific numbers and says what they show about the population
Numbers are listed but not connected to the claim
Reasoning
All four links named: variation, inheritance, differential survival or reproduction, change over generations
Two or three links present, or the explanation relies on need or effort
Testing the Explanation
Proposes a fair test that could show heritability or the selective agent
Test named but it cannot separate heritable from environmental causes
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Every data set is invented for practice and patterned on real studies. 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 condition must be met for natural selection to change a trait in a population over generations?
Answer: B
Selection can only shift a population if individuals differ and those differences are passed to offspring. Choice A is a common misconception: mutations arise at random, not because the environment calls for them. Choice C describes changes in individuals, which are not inherited. Population size (D) affects how chance acts, but it is not a requirement.
Question 2 of 20 · Multiple Choice
In an invented sample of 100 plants, 36 are AA, 48 are Aa and 16 are aa. What is the frequency of allele A?
Answer: C
There are 200 copies of the gene. A copies = 2 x 36 + 48 = 120, and 120/200 = 0.60. Choice A counts only the AA plants. Choice D adds the AA and Aa plants (84 of 100), which gives the share of plants with at least one A, not the allele frequency.
Question 3 of 20 · Multiple Choice
Which statement uses the word adaptation the way evolutionary biologists do?
Answer: A
Adaptation by natural selection is a change in a population over generations. Choices B, C and D are changes within one individual's life (acclimation, growth responses, training), which are not passed on through genes.
Question 4 of 20 · Multiple Choice
Guppies were moved from a stream full of predatory fish to a pool above a waterfall with no predators. After about 15 generations, the males in the pool were more brightly colored. Which explanation fits the evidence best?
Answer: D
Choice D names the heritable variation, the change in the environment (no predators) and the effect on reproduction. Choice A explains change by need. Choice B wrongly says the environment causes the mutations. Choice C describes individual change, which would not carry into offspring.
Question 5 of 20 · Multiple Choice
In an invented predation study on a rocky shore, 120 of 200 thick-shelled snails and 45 of 150 thin-shelled snails survived a season with crabs. What are the survival proportions?
Answer: A
120/200 = 0.60 and 45/150 = 0.30, so thick-shelled snails survived twice as often. Choice B divides each count by the total number of survivors (165), which gives the share of survivors, not survival. Choice C divides 45 by 100. Choice D divides by 100 for both, which gives a survival above 1, a sign of an error.
Question 6 of 20 · Multiple Choice
Yarrow plants from high mountain slopes are shorter than yarrow plants from valleys. Which evidence would best show that the difference is a heritable adaptation and not just a direct effect of the cold?
Answer: B
A common garden removes the environmental difference; if the height difference remains, it is inherited. Choice A only repeats the original observation. Choices C and D are other differences that do not separate genes from environment.
Question 7 of 20 · Multiple Choice
In Diagram 1, what would the model predict if light mice survived exactly as well as dark mice (s = 0)?
Answer: C
With s = 0, p' = p / (1 - 0) = p, so the frequency does not change: there is no selection. Choices A and D assume change without any survival difference. Choice B would need light mice to have the advantage.
Question 8 of 20 · Multiple Choice
Over 20 invented years of hotter summers, the frequency of a heat-tolerance allele in a population of intertidal snails rose from 0.15 to 0.42. What was the average change per year?
Answer: B
The total change is 0.42 - 0.15 = 0.27, and 0.27/20 = 0.0135 per year. Choice D is the total change, not the change per year. Choice A divides 0.15 by 20, and choice C divides 0.42 by 20.
Question 9 of 20 · Multiple Choice
A student says: "When the climate got colder, the rabbits' bodies made the mutation for thicker fur." What is the main problem with this claim?
Answer: D
New alleles come from random mutations that happen whether or not they help. The environment then affects which alleles are passed on. Choices A and B are false: fur traits do have a genetic basis. Choice C is an overstatement and does not address the error.
Question 10 of 20 · Multiple Choice
Which of these is a biotic difference that can drive adaptation?
Answer: A
Biotic factors are living things, including the evolution of other organisms, like prey that becomes more toxic. Choices B, C and D are abiotic: acidity, temperature ranges and light.
Question 11 of 20 · Multiple Choice
Which situation would make adaptation by natural selection slowest?
Answer: B
If differences in a trait are not inherited, survivors do not pass them on, so the next generation does not shift. Choices A, C and D all speed up adaptation: a large reproductive advantage, short generations and strong effects on survival.
Question 12 of 20 · Multiple Choice
After an invasive crab spread along a coast, a snail population on that coast had thicker shells than it had 80 years earlier. Which additional evidence would most strengthen the claim that crabs caused the change by natural selection?
Answer: A
A comparison group without crabs, from the same time, rules out a change that affected every snail population, such as a change in water chemistry. Choices B and C are true facts but do not test the cause. Choice D describes something that stayed the same, which cannot explain a change.
Question 13 of 20 · Multiple Choice
A population of beetles has no variation in body color: all are brown. The soil around them turns much darker. What will natural selection do to body color?
Answer: C
Selection sorts existing heritable variation. With no color variation, there is nothing to favor until a mutation produces a new color. Choices A and D assume variation that is not there, and choice B describes a change within individuals.
Question 14 of 20 · Multiple Choice
Two populations of one plant species live on opposite sides of a high mountain range, one side dry and one side wet. Why can they adapt to different conditions?
Answer: D
A geographic barrier cuts gene flow, so alleles favored on one side are not diluted by alleles from the other side. Choice B wrongly ties mutations to the environment. Choice A is an unsupported rule, and choice C is false: each population keeps reproducing.
Question 15 of 20 · Short Answer
Plantain plants from a salt marsh and from an inland field are grown from seed in the same salty soil. In an invented trial, 46 of 50 salt-marsh plants and 12 of 50 inland plants survive to flower. Find each survival proportion and explain what the result shows.
Salt marsh: 46/50 = 0.92. Inland: 12/50 = 0.24. Because both groups grew in the same soil, the difference is heritable. In the salt marsh, plants with alleles for salt tolerance survived and set seed more often, so over generations the marsh population became salt tolerant: an adaptation to that abiotic condition.
Question 16 of 20 · Short Answer
On an island, the flowers a hummingbird feeds on have nectar tubes about 30 mm long, and the birds' bills average 28 mm. On the mainland, the flowers' tubes are about 20 mm long and the same species' bills average 19 mm. Construct an explanation for the island birds' longer bills.
Claim: island birds have adapted to the longer flowers. Evidence: bill length matches tube length in both places (28 mm with 30 mm tubes, 19 mm with 20 mm tubes). Reasoning: bill length varies and is inherited. On the island, birds with longer bills reach more nectar, so they get more energy and raise more young. Over generations the alleles for long bills became more common. This is adaptation to another organism, the flower.
Question 17 of 20 · Short Answer
A model population on brown soil has 300 green beetles and 100 brown beetles. Each generation, birds eat 40% of the green beetles and 10% of the brown beetles, and every survivor leaves two offspring of its own color (the parents die). What fraction of the beetles is brown after one generation?
Survivors: 300 x 0.60 = 180 green and 100 x 0.90 = 90 brown. Doubling does not change the proportions (360 and 180), so the brown fraction is 90/270 = 1/3, about 0.33, up from 100/400 = 0.25.
Question 18 of 20 · Short Answer
A student writes: "Cave fish lost their eyes because they never used them." Critique the explanation and rewrite it using natural selection.
The explanation treats disuse by individuals as something passed on, but offspring inherit alleles, not the effects of use. A better explanation: eye size varied among the cave fish, partly because of their alleles. In total darkness, eyes gave no survival advantage, so alleles that reduced eyes were not selected against, and building eyes costs energy, so fish that spent less on eyes may have grown or bred better. Over many generations, alleles for small or no eyes became common. (Chance changes in allele frequency can also play a part.)
Question 19 of 20 · Short Answer
Over 30 years of warmer springs, a wild mustard population began flowering 6 days earlier. Seeds saved in 1990 and seeds collected in 2020 were grown side by side in one greenhouse, and the 2020 plants flowered 4 days earlier. What fraction of the field shift is heritable, and what does the result show?
The heritable part is 4/6, about 0.67 of the 6-day shift. Because both seed groups grew in identical conditions, the 4-day difference comes from their alleles: the population has evolved earlier flowering, likely because plants that flowered early set more seed before the warm, dry summer. The other 2 days come from the direct effect of warmer springs on each plant.
Question 20 of 20 · Short Answer
Lizards living in a city have longer limbs than lizards of the same species in nearby forest. Plan how you would collect evidence that this is an adaptation to city surfaces such as walls and pavement.
(1) Measure limb length in several city and forest populations to show the pattern repeats. (2) Raise hatchlings from both habitats in the same lab conditions; if city hatchlings still grow longer limbs, the difference is heritable. (3) Test running and clinging on smooth vertical surfaces to show that longer limbs help on city surfaces. (4) Track survival or number of offspring by limb length in a city population over several years, and compare allele or trait frequencies across generations.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS4-4 mean?
HS-LS4-4 asks students to construct an explanation, based on evidence, of how natural selection makes populations adapted to their environments. Students use data, such as allele frequencies or survival rates, to show that an environmental difference favors some heritable variants, which then become more common over generations. The code means High School, Life Science, core idea 4 (Biological Evolution: Unity and Diversity), performance expectation 4.
Is HS-LS4-4 taught in Biology?
Yes, it is usually taught in the evolution unit of high school Biology, and sometimes in an integrated science or environmental science course. It builds on the middle school standards MS-LS4-4 and MS-LS4-6 and uses only basic math: fractions, percents and comparing means.
What is the difference between natural selection and adaptation?
Natural selection is the process, and adaptation is its result. Selection is the difference in survival and reproduction among individuals with different heritable traits. Adaptation is the change that builds up in the population over generations, and the word also names a trait that has become common because of it.
Can an individual organism adapt by natural selection?
No: individuals survive or die and reproduce more or less, but their genes do not change to fit the environment. Populations adapt, because the share of individuals carrying favored alleles grows from one generation to the next. Changes during one life, such as a tan or bigger muscles, are not passed on through genes.
What kind of evidence do students use for HS-LS4-4?
The Clarification Statement puts the emphasis on data showing how specific differences in ecosystems change gene frequency over time. Good evidence includes allele or trait frequencies in populations living under different conditions, survival or reproduction rates of different variants, measurements before and after an event, and common-garden experiments that show a difference is inherited.
How do you calculate allele frequency?
Count the copies of the allele and divide by the total number of copies of the gene. In a sample of N individuals with two copies each, the frequency of allele A is (2 x number of AA + number of Aa) / 2N. Dividing by N instead of 2N is a frequent mistake.
What are good real examples of natural selection leading to adaptation?
Well-studied cases include dark and light pocket mice on lava and sand, beak depth in Galapagos finches after droughts, armor plates in lake stickleback and toxin resistance in garter snakes that eat toxic newts. On this page the numbers for each case are invented for teaching, but the patterns follow the published studies.
What mistakes do students often make with natural selection?
A frequent error is explaining change by need or effort ("the finches needed deeper beaks"). Others include thinking the environment causes the right mutations, thinking individuals evolve, and treating any difference between populations as genetic without evidence that it is inherited. Asking "which individuals survived and had more offspring?" usually exposes the error.
Does HS-LS4-4 have an assessment boundary?
No, NGSS lists no Assessment Boundary for HS-LS4-4. The Clarification Statement sets the focus: using data to show how biotic and abiotic differences, such as seasonal temperature ranges, climate change, acidity, light, geographic barriers or the evolution of other organisms, change gene frequency and lead to adaptation.
How does HS-LS4-4 connect to other standards?
It follows MS-LS4-4 and MS-LS4-6, where students first explain and model natural selection. In high school it works alongside HS-LS4-2 (the four factors of evolution) and HS-LS4-3 (statistics of advantageous traits), and it leads to HS-LS4-5, where students evaluate how environmental change can increase some species, give rise to new species or drive others extinct.
07
Related Standards
5 standards
These standards connect to HS-LS4-4: 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 in traits raises some individuals' chance to survive and reproduce
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