Evolution and Natural Selection
How populations change over time
Evolution and Natural Selection
How populations change over time
Biology - Grade 6-8
- 1
Define evolution in your own words.
Focus on populations changing over time, not a single organism changing during its life.
Evolution is the change in the inherited traits of a population over many generations. - 2
Define natural selection in your own words.
Natural selection is the process in which individuals with helpful inherited traits are more likely to survive and reproduce, so those traits become more common in a population over time. - 3
A population of beetles has green and brown individuals. Birds can easily see the green beetles on dark soil. Explain which color beetle is more likely to become common over many generations and why.
Think about camouflage and survival.
Brown beetles are more likely to become common because they are better camouflaged on dark soil. Birds eat more green beetles, so brown beetles survive and reproduce more often, passing their traits to offspring. - 4
Explain the difference between a learned behavior and an inherited trait. Give one example of each.
A learned behavior is something an organism gains through experience, such as a dog learning to sit. An inherited trait is passed from parents to offspring, such as fur color in rabbits. - 5
A student says, "Individual giraffes stretched their necks, so they grew longer necks and passed that change to their babies." Explain why this statement does not describe natural selection correctly.
Remember that inherited variation already exists in a population.
This statement is incorrect because individual giraffes do not change their inherited traits by stretching. Natural selection works when some giraffes are born with slightly longer necks, and those giraffes are more likely to survive and have offspring, so long necks become more common over time. - 6
Why is variation within a population important for natural selection?
Variation is important because individuals in a population are not exactly the same. If some individuals have traits that help them survive in a certain environment, they are more likely to reproduce and pass those traits on. - 7
Describe one adaptation that helps a desert animal survive, and explain how it helps.
Choose a body feature, behavior, or internal process that improves survival.
One desert adaptation is large ears in a fennec fox. Large ears help release body heat, which helps the animal stay cool in a hot environment. - 8
A disease kills many bacteria in a population, but a few bacteria survive because they have resistance to the medicine. Explain what may happen to the bacterial population after several generations.
After several generations, the bacterial population may become mostly resistant to the medicine. The resistant bacteria survive and reproduce, so the resistance trait becomes more common in the population. - 9
What is the difference between an adaptation and a habitat?
One is a helpful characteristic, and the other is the organism's home environment.
An adaptation is a trait or behavior that helps an organism survive and reproduce. A habitat is the place or environment where an organism lives. - 10
Some rabbits in a snowy area have white fur and some have brown fur. In winter, foxes catch more brown rabbits. Predict how the rabbit population may change over time.
Over time, the population may have more white rabbits because white fur helps them blend into the snow. White rabbits are more likely to survive and reproduce, so white fur becomes more common. - 11
Explain why natural selection acts on individuals but evolution happens in populations.
Think about what is selected and what actually changes over time.
Natural selection affects individuals because each organism either survives and reproduces or does not. Evolution happens in populations because the overall frequency of traits changes across many generations. - 12
A sudden climate change makes a wet environment much drier. Explain how this environmental change could affect which traits are favored by natural selection.
A drier environment may favor traits that help organisms conserve water, find shade, or tolerate heat. Individuals with those helpful inherited traits are more likely to survive and reproduce, so those traits may become more common over time.