AP Biology:: Natural Selection

What is EVOLUTION, at a general biological level?

- **A)** Evolution refers to a change occurring within a SINGLE individual organism's own DNA during its lifetime, rather than across generations of a population
- **B)** The CHANGE in the genetic makeup (specifically ALLELE FREQUENCIES) of a POPULATION over successive generations
- **C)** This term has no actual relationship to changes in a population's genetic makeup over time
- **D)** Evolution always requires that EVERY individual in a population changes identically and simultaneously

What is NATURAL SELECTION, as one mechanism that can drive evolution?

- **A)** Natural selection refers to a random, non-directional process with no actual relationship to which traits get passed on more frequently
- **B)** The process by which individuals with certain HERITABLE traits that improve SURVIVAL and/or REPRODUCTION in a given environment tend to leave MORE offspring than individuals without those traits, gradually increasing the frequency of those advantageous traits in the population
- **C)** This mechanism always results in EVERY individual in a population having exactly the SAME reproductive success, regardless of their traits
- **D)** Natural selection acts directly on an organism's genotype, with no actual relationship to its observable phenotype or reproductive success

What THREE conditions must generally be met for NATURAL SELECTION to occur within a population?

- **A)** These conditions have no actual relationship to whether natural selection can occur within a population
- **B)** (1) VARIATION must exist for a trait, (2) that variation must be HERITABLE (passable to offspring), and (3) the variation must lead to DIFFERENCES in survival and/or reproductive success
- **C)** Natural selection requires that every individual in the population be genetically IDENTICAL, with no variation in any trait
- **D)** Natural selection requires that a trait's variation NOT be heritable, so that offspring never inherit their parents' traits

What is FITNESS, in the specific evolutionary biology sense of the term (as opposed to its everyday meaning of physical health)?

- **A)** Fitness refers only to an organism's physical strength or speed, with no actual relationship to its reproductive success
- **B)** A measure of an individual's RELATIVE REPRODUCTIVE SUCCESS -- specifically, how many surviving, fertile OFFSPRING it produces compared to other individuals in the population
- **C)** Fitness is always identical for every individual within a species, regardless of their specific traits
- **D)** This term has no actual relationship to how many offspring an individual produces

What is an ADAPTATION, in an evolutionary context?

- **A)** This term has no actual relationship to a trait's effect on an organism's fitness within its environment
- **B)** Adaptations always REDUCE an organism's fitness within its environment, rather than increasing it
- **C)** An adaptation refers to a trait an individual organism acquires during its own lifetime through practice or exposure, which is then passed on genetically to its offspring
- **D)** A HERITABLE trait that has become common in a population BECAUSE it increases an organism's fitness (survival and/or reproductive success) in its particular environment

What is DIRECTIONAL SELECTION, as one of the three general patterns of natural selection?

- **A)** Directional selection favors individuals with the AVERAGE, intermediate value of a trait, rather than individuals at one extreme
- **B)** This pattern has no actual relationship to shifting a population's average trait value over time
- **C)** Directional selection always favors BOTH extremes of a trait simultaneously, rather than just one
- **D)** A pattern where individuals at ONE EXTREME of a trait's range have HIGHER fitness, causing the population's average trait value to SHIFT in that direction over time

What is STABILIZING SELECTION, as another pattern of natural selection?

- **A)** A pattern where individuals with the INTERMEDIATE (average) value of a trait have HIGHER fitness, while individuals at EITHER extreme have lower fitness, reducing the population's overall variation for that trait over time
- **B)** This pattern has no actual relationship to reducing a population's variation for a given trait
- **C)** Stabilizing selection favors individuals at BOTH extremes of a trait's range, rather than the intermediate value
- **D)** Stabilizing selection always increases a population's variation for a trait over time, rather than reducing it

What is DISRUPTIVE SELECTION, as the third general pattern of natural selection?

- **A)** A pattern where individuals at BOTH extremes of a trait's range have HIGHER fitness than individuals with the intermediate value, potentially splitting the population into two distinct trait groups over time
- **B)** This pattern has no actual relationship to favoring individuals at the extremes of a trait's range
- **C)** Disruptive selection favors only the intermediate, average value of a trait, identical to stabilizing selection
- **D)** Disruptive selection always results in EVERY individual converging on exactly the same single trait value