7th grade · Science · Unit 8 of 18
Natural Selection
How species adapt and change
What your child practices
Variation, inherited versus acquired traits, adaptations, and how natural selection changes populations over generations, with fossils and other evidence. Includes reading data from a predator–prey model.
Texas Essential Knowledge and Skills (TEKS) teks student expectation: 7.13(D) · natural and artificial selection changing traits over generations
How we explain it
Children can open this short lesson before they practice.
- Inherited traits come from parents in genes. Acquired traits are learned or gained during one life and are not passed on.
- Members of a species vary. Those best suited to their surroundings survive and have more young.
- Over many generations, the helpful traits become more common in the population.
Example: Mice live on dark soil, and owls hunt them by sight. Which mice will become more common? Owls spot light mice more easily on dark soil. Dark mice survive and have more young. Their color is inherited, so it spreads. Answer: dark mice
Natural Selection in Texas
In the Texas Essential Knowledge and Skills (TEKS), this is unit 8 of 18 in 7th grade Science, after Our Solar System and before Food Chains & Energy.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Source: Texas Education Agency (TEA)
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A class modeled lizards living on black volcanic rock. Hawks hunt them by sight. What best explains the pattern in the table?
A sample of 100 lizards in each generation Generation Dark lizards Pale lizards 1 43 57 2 55 45 3 67 33 4 75 25 - Pale lizards change color during their lives to match the ground
- The lizards decide to have dark offspring so they can hide
- Hawks cannot see any of the lizards at all
- Dark lizards are harder for hawks to spot, so more survive and reproduce
Dark lizards are harder for hawks to spot, so more survive and reproduce
Hint: Individuals can't change their inherited color. Those that blend in are eaten less, so they live to pass their color on to more offspring.
Question 2
Snowshoe hares turn white in winter. How does this help them survive?
🐇- It camouflages them against the snow
- It makes them taste bad to predators
- It lets them see in the dark
- It helps them swim faster
It camouflages them against the snow
Hint: Think about what a predator sees. A white hare on white snow is hard to spot.
Question 3
Farmers breed only the cows that give the most milk. Over many generations, the herd gives more milk. This is called…
🐄- camouflage
- artificial (selective) breeding
- natural selection
- extinction
artificial (selective) breeding
Hint: Here people, not nature, choose which animals reproduce.
Question 4
Bacteria are treated with an antibiotic. A few have a trait that lets them survive it. What happens over many generations?
🧫- All bacteria disappear forever
- Antibiotic-resistant bacteria become more common
- Nothing changes in the population
- The bacteria learn to resist the drug on purpose
Antibiotic-resistant bacteria become more common
Hint: The survivors reproduce and pass on their resistance. This is natural selection happening fast.
Question 5
Whales have small hip bones that they do not use for walking. What do scientists think this shows?
🐋- Whales evolved from ancestors that walked on land
- Whales will soon grow legs again
- Whales and fish have the same skeleton
- Whales use the bones to dig in the sea floor
Whales evolved from ancestors that walked on land
Hint: Fossils show early whale relatives with four legs. The tiny hip bones are leftovers from those ancestors.
Question 6
Inherited or acquired? Sort each trait.
Sort into: 🧬 inherited (in the genes) · 🏋️ acquired during life
- 🐕a dog that learned to sit
- 🌵a cactus's sharp spines
- 🌺a flower's petal color
- 🌳a branch bent by strong winds
- 🚲knowing how to ride a bike
- 💪muscles built by lifting weights
- 🐦a finch's beak shape
- 🐅a tiger's stripe pattern
🧬 inherited (in the genes): a cactus's sharp spines, a flower's petal color, a finch's beak shape, a tiger's stripe pattern · 🏋️ acquired during life: a dog that learned to sit, a branch bent by strong winds, knowing how to ride a bike, muscles built by lifting weights
Hint: Inherited traits are passed from parents to offspring in their genes. Acquired traits are gained during one organism's life and are not passed on to its offspring.