MS-LS4-6: Modeling Trait Changes Over Generations
Also called NGSS MS-LS4-6 · Topic: Natural Selection and Adaptations · Life Science
The Official Wording
Use mathematical representations to support explanations of how natural selection may lead to increases and decreases of specific traits in populations over time.
Clarification statement: Emphasis is on using mathematical models, probability statements, and proportional reasoning to support explanations of trends in changes to populations over time.
Assessment boundary: Assessment does not include Hardy Weinberg calculations.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What MS-LS4-6 Means in Plain English
Middle schoolers use numbers, like percentages, ratios and graphs, to show how natural selection makes a trait more or less common over generations. They track a population, see which variety survives more often, and calculate how its share of the population grows.
The math stays at percents, proportions and simple probability, with no population genetics formulas such as Hardy-Weinberg. It extends survival explanations from one generation (MS-LS4-4) and prepares students for high school models of adaptation (HS-LS4-3).
MS-LS4-6 I Can Statements
- I can calculate the percent of a population that has a trait.
- I can graph how a trait's share changes across generations.
- I can use data to explain why a trait became more common.
MS-LS4-6 Worked Example
A camouflage simulation run on a sheet of green felt, with the math done after each round.
Over several generations, what happens to the share of green chips hidden on green felt?
Set It Up: A large sheet of green felt, a supply of green and orange paper chips, a stopwatch and a data table.
- Scatter 50 green and 50 orange chips on the felt.Generation 1: 50% green
- Hunters pick up chips one at a time until 50 are caught.Caught: 35 orange, 15 green
- Each of the 50 survivors adds one chip of its own color as offspring.Generation 2: 70 green, 30 orange, 70% green
- Hunt again until 50 are caught, then refill the same way.Caught: 25 orange, 25 green. Generation 3: 90% green
- Plot percent green against generation on graph paper.50%, 70%, 90%: a rising line
Green chips went from 50% to 90% of the population in two rounds of hunting.
Why it works: Green chips were harder to spot, so more survived to reproduce, and each generation started with a larger share of green.
Common Mistakes with MS-LS4-6
Comparing counts instead of percents
“There are more green chips, so green is winning,” when the totals differ
Try this: Divide each count by the population total before comparing generations, because the population size can change from one round to the next.
Thinking individuals change color
“The orange chips turned green to hide.”
Try this: No chip changes color. The population changes because green chips survive and reproduce more, so their share grows each generation.
Expecting the trait to vanish at once
“After one round, all the orange chips should be gone.”
Try this: Selection shifts proportions gradually. Some orange chips survive by chance each round, so the change shows up over several generations.
Where MS-LS4-6 Fits
Practice MS-LS4-6
Quick Check
- A population has 40 brown mice and 60 white mice. What percent are brown?
- On dark soil, brown mice survive more often. What happens to the percent of brown mice over generations?
- Why graph the percent instead of just the count of brown mice?