HS-LS4-2: The Four Causes of Evolution
Also called NGSS HS-LS4-2 · Topic: Natural Selection and Evolution · Life Science
The Official Wording
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.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-LS4-2 Means in Plain English
Students explain evolution by natural selection as four factors working together: populations produce more young than can survive, individuals differ in inherited traits, they compete for limited food and space, and those better suited to the environment leave more offspring, so their traits spread.
Evidence can be simple graphs and proportional reasoning. Other mechanisms such as genetic drift, gene flow and coevolution are left for later study. It builds on MS-LS4-4 and MS-LS4-6 and supports HS-LS4-3 and HS-LS4-4.
HS-LS4-2 I Can Statements
- I can name the four factors that drive natural selection.
- I can explain how competition for resources affects survival.
- I can use data to show a trait spreading in a population.
HS-LS4-2 Worked Example
A tabletop simulation where students play squirrels gathering a limited pile of acorns before winter.
When acorns are limited, do squirrels with a faster gathering trait become more common over generations?
Set It Up: A tray of 40 acorns or dried beans, squirrel cards marked fast or slow, a cup for drawing turn order and a data table.
- Start with 6 fast and 6 slow squirrels. In random turns, fast squirrels take 2 acorns and slow squirrels take 1 until the tray is empty.Limited food: 40 acorns for 12 squirrels
- Squirrels with at least 3 acorns survive the winter, and each survivor has two young that inherit its card.Survivors: 6 fast, 2 slow
- Play the next generation with the 16 young and a fresh tray of 40 acorns.Start: 12 fast, 4 slow (75% fast)
- Apply the same survival and offspring rules.Survivors: 6 fast, 0 slow
- Graph the percent of fast squirrels in each generation.50%, then 75%, then 100%
Because acorns ran short, fast gatherers survived and reproduced more, and the fast trait went from half the population to all of it in two generations.
Why it works: More young are born than the food can support, so inherited differences decide who survives, and the traits of the survivors become more common.
Common Mistakes with HS-LS4-2
Animals change because they need to
“The squirrels got faster because they had to”
Try this: Individuals do not change their inherited traits on demand. The population changes because individuals with useful traits leave more offspring.
Skipping overproduction
An explanation that never says why some must die
Try this: Point out that more young are born than resources can support, which is what makes competition and selection unavoidable.
Using traits that are not inherited
“A squirrel that got stronger from climbing passes strength to its babies”
Try this: Only traits coded in genes pass to offspring. Strength built through exercise during a lifetime is not inherited.
Where HS-LS4-2 Fits
Practice HS-LS4-2
Quick Check
- Name the four factors that drive evolution by natural selection.
- If food were unlimited in the squirrel game, would the fast trait spread as quickly?
- Where does the variation that natural selection acts on come from?