Factors of Natural Selection
An inherited trait that increases an organism’s chance of survival and reproduction in a specific environment.
adaptation
Structures that are similar in different species because they were inherited from a common ancestor.
homologous structures
A population of rabbits includes white and brown individuals. After a snowy winter, most of the rabbits seen are white. Which color had a survival advantage in this environment?
White
A population of foxes has both white and brown fur. The area they live in is mostly snowy. Which foxes are more likely to survive, and why?
White foxes are more likely to survive because they blend in with the snow and avoid predators.
Fossils show that some species that once lived on Earth no longer exist. What is this called?
Extinction.
This process explains why individuals with favorable traits are more likely to survive and reproduce than others.
natural selection
This type of evidence shows how species have changed over long periods of time through preserved remains in rock layers.
fossil record
A graph shows the frequency of a green allele in a plant population over 10 generations. The frequency rises from 20% to 70%. What does this change in allele frequency suggest about the green allele?
It provides a survival or reproductive advantage.
Why does having differences (variation) in a population help some individuals survive better than others?
Variation gives some individuals traits that help them survive and reproduce in their environment.
Two species of birds live on different islands. Over thousands of years, they develop different beak shapes. What evolutionary process does this demonstrate?
Speciation – they became separate species because of environmental differences.
Variation, overproduction of offspring, competition for resources, and differential survival and reproduction.
the four conditions required for natural selection to occur
Similarities in DNA and protein sequences that indicate how closely related different species are.
molecular (genetic) evidence
In a population of beetles, only 25% have long wings. Birds preferentially eat short-winged beetles. Over several generations, the percentage of long-winged beetles increases. Explain how probability and differential survival affect the population’s traits.
Beetles with long wings survive more and reproduce more, so the trait becomes more common.
Some fish have longer fins that help them swim faster. Over many generations, most fish have long fins. Explain what caused this change.
Fish with longer fins survive better and have more babies, so over time, more fish have long fins.
Scientists compare DNA from humans, chimpanzees, and gorillas. They find many similarities. How does this support the idea of common ancestry?
Similar DNA suggests they share a common ancestor and evolved into different species over time.
In a population of beetles, birds more easily see and eat green beetles than brown beetles on dark soil, causing the brown beetle population to increase over time.
natural selection due to environmental selective pressure
The forelimbs of humans, bats, and whales have different functions but similar bone structures provides evidence of _______________
common ancestry
Two islands have the same species of lizards. On Island A, insects are mostly on tall plants; on Island B, insects are mostly on the ground. Lizards with longer legs are more successful on Island A. How do environmental differences on the two islands influence natural selection?
Different selective pressures favor different traits in each population.
A population of lizards lives in an area with both rocks and sand. Some lizards are gray, and some are tan. Predators can see lizards that stand out against their background. Over many generations, the population has more gray lizards near rocks and more tan lizards near sand. Explain how natural selection caused this pattern.
Lizards that match their background survive predators more and reproduce more. Over generations, the population becomes adapted to their specific environments, with gray lizards on rocks and tan lizards on sand.
Fossils show a species of horse gradually developing longer legs and different teeth over millions of years. Some related species disappeared during this time. Explain what these changes show about evolution and extinction.
They show that species adapt to changing environments, and some species go extinct if they cannot adapt. Evolution and extinction are linked processes.
A graph shows that over 10 generations, the percentage of mice with light fur decreases while the percentage with dark fur increases after the environment becomes darker. Create a valid scientific question based on this prompt
How does natural selection explain the change in fur color frequencies in the mouse population over time?
An evolutionary tree shows five species: W, X, Y, Z, and V. Species W and X share a recent node; Species Y branches off before W and X; Species Z and V share a separate node. Based on the tree, which two species are most closely related, and what does the branching node between them represent?
W and X; common ancestor
A population of fish has variation in gill size. Over 20 generations, water oxygen levels drop. Data show that fish with larger gills survive at a higher rate, and the allele for large gills increases in frequency. Using the data, explain how natural selection and allele frequency changes support evolution in this population.
Fish with larger gills survive and reproduce more, so the allele for large gills becomes more common, showing evolution by natural selection.
A species of bird eats seeds of different sizes. Some birds have short beaks, and some have long beaks. Over 50 years, scientists observe that most birds have medium-length beaks. Explain why this happened and how natural selection shaped the population.
Birds with very short or very long beaks were less successful at eating the most common seed sizes. Birds with medium-length beaks survived and reproduced more, so over time, medium beaks became the most common. Natural selection favored the trait that matched the environment.
Scientists study a group of insects that were separated by a mountain range. Over many generations, they develop different mating behaviors and can no longer produce fertile offspring with each other. How does this provide evidence for speciation, and what role does natural selection play?
Natural selection caused adaptations to different environments, and reproductive isolation led to speciation, a new species formed because the populations could no longer interbreed.