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ap biology unit 7 study guides

natural selection

7.0

Unit 7 Overview: Natural Selection

7.1

Introduction to Natural Selection

7.2

Natural Selection

7.3

Artificial Selection

7.4

Population Genetics

7.5

Hardy-Weinberg Equilibrium

7.6

Evidence of Evolution

7.7

Common Ancestry

7.8

Continuing Evolution

7.9

Phylogeny

7.10

Speciation

7.11

Variations in Populations

7.12

Origins of Life

7.13

Origin of Life on Earth

unit 7 review

Natural selection is the process by which organisms adapt to their environment over generations. This fundamental concept in biology explains how populations evolve, with traits that enhance survival and reproduction becoming more common over time. Darwin's observations during his voyage on the HMS Beagle led to the development of this theory. Evidence from fossils, comparative anatomy, and molecular biology supports natural selection as the driving force behind the diversity of life on Earth.

Key Concepts and Definitions

  • Natural selection process by which populations become adapted to their environment over the course of generations
  • Adaptation a trait that increases an organism's fitness and arises through natural selection
    • Can be morphological (physical), physiological, or behavioral
  • Fitness the ability to survive and reproduce in a specific environment
  • Variation the presence of differences among individuals in a population
    • Variation is necessary for natural selection to occur
  • Inheritance the passing of traits from parents to offspring
  • Differential reproduction occurs when individuals with certain traits leave more offspring than individuals without those traits
  • Speciation the formation of new species as a result of evolution by natural selection

Historical Context and Darwin's Contributions

  • Charles Darwin developed the theory of evolution by natural selection in the mid-19th century
  • Darwin's voyage on the HMS Beagle exposed him to diverse flora and fauna and geological evidence that influenced his thinking
  • Darwin observed that organisms seemed well-suited to their environments and that similar species often differed across geographic regions
  • Alfred Russel Wallace independently developed a theory of evolution by natural selection and corresponded with Darwin
  • Darwin's book "On the Origin of Species" (1859) outlined his evidence for evolution and proposed natural selection as the mechanism
    • The book was controversial at the time but eventually gained widespread acceptance in the scientific community
  • Darwin's theory built upon earlier ideas, such as Lamarck's concept of the inheritance of acquired characteristics
  • Modern evolutionary theory synthesizes Darwin's ideas with Mendelian genetics and other scientific discoveries

Mechanisms of Natural Selection

  • Overproduction more offspring are produced than can survive due to limited resources
  • Genetic variation exists within populations for traits that affect survival and reproduction
    • Variation arises through mutation, recombination during sexual reproduction, and gene flow between populations
  • Differential survival and reproduction individuals with traits that are advantageous in a given environment tend to survive and reproduce more than those without those traits
    • Over time, this leads to a change in the frequency of alleles in the population
  • Heredity traits that confer an advantage are passed down to offspring
  • Accumulation of changes over many generations, the advantageous traits become more common in the population
  • Adaptation to the environment results from the gradual accumulation of beneficial traits
  • Speciation can occur when populations become reproductively isolated and diverge due to different selective pressures

Evidence for Natural Selection

  • Fossil record shows gradual changes in organisms over time and the existence of extinct species
    • Transitional fossils demonstrate the evolution of one species into another
  • Comparative anatomy reveals structural similarities among related species, suggesting common ancestry
    • Homologous structures (e.g., human arm, bat wing, whale flipper) have similar underlying anatomy due to shared ancestry
    • Analogous structures (e.g., bird wing, insect wing) have similar functions but different underlying anatomy due to convergent evolution
  • Embryology early developmental stages of different species show similarities, supporting common ancestry
  • Molecular biology DNA and protein sequences show similarities among related species
    • The degree of similarity reflects the relatedness of species
  • Biogeography the distribution of species across geographic regions reflects their evolutionary history
    • Island species often resemble nearby mainland species but with unique adaptations
  • Observed instances of natural selection (e.g., antibiotic resistance in bacteria, beak shape changes in Galápagos finches)

Types of Selection

  • Directional selection favors individuals at one extreme of a trait distribution
    • Leads to a shift in the population's mean trait value over time
  • Stabilizing selection favors individuals with intermediate trait values
    • Reduces variation in the population and maintains the mean trait value
  • Disruptive selection favors individuals at both extremes of a trait distribution
    • Can lead to the formation of distinct subpopulations or even new species
  • Sexual selection occurs when traits that enhance mating success are favored
    • Can result in the evolution of exaggerated traits (e.g., peacock tail)
  • Artificial selection human-driven selection for desired traits in domesticated plants and animals
    • Demonstrates the power of selection to alter populations

Adaptation and Fitness

  • Adaptation an inherited trait that enhances an organism's fitness in a specific environment
  • Fitness the ability to survive and reproduce in a given environment
    • Measured by an individual's relative contribution to the next generation
  • Adaptations can take many forms, such as morphological, physiological, or behavioral traits
    • Examples: camouflage, antibiotic resistance, courtship rituals
  • Adaptations are specific to the environment in which they evolved
    • A trait that is adaptive in one environment may be neutral or maladaptive in another
  • Fitness is always relative to the environment and other individuals in the population
  • Trade-offs often exist between different adaptations
    • Allocating resources to one trait may come at the expense of another

Natural Selection in Action: Case Studies

  • Peppered moth evolution in response to industrial pollution in England
    • Light-colored moths were better camouflaged on light-colored trees before pollution
    • Dark-colored moths became more common as pollution darkened tree bark
  • Galápagos finches' beak adaptations for different food sources
    • Finches with larger, stronger beaks are better adapted for cracking tough seeds
    • Finches with smaller, pointier beaks are better adapted for catching insects
  • Antibiotic resistance in bacteria
    • Bacteria with mutations conferring resistance survive and reproduce in the presence of antibiotics
    • Resistant strains become more common over time
  • Sickle cell anemia and malaria resistance
    • Having one copy of the sickle cell allele confers resistance to malaria
    • The allele persists in populations where malaria is prevalent despite the negative effects of having two copies

Challenges and Misconceptions

  • Evolution is often misunderstood as a purposeful or directed process
    • Natural selection is a result of random variation and differential survival and reproduction
  • Adaptation is sometimes misinterpreted as an individual actively trying to adapt
    • Adaptations arise through the selection of inherited traits over many generations
  • The phrase "survival of the fittest" is often misinterpreted to mean the strongest or most aggressive individuals
    • Fitness refers to the ability to survive and reproduce, which can involve cooperation and other strategies
  • Evolution is sometimes wrongly equated with progress or improvement
    • Natural selection favors traits that enhance fitness in a specific environment, not inherently "better" traits
  • The role of chance and random events in evolution is often underestimated
    • Genetic drift, founder effects, and bottlenecks can significantly influence evolutionary outcomes
  • Misconceptions about the relationship between evolution and religion persist
    • Many religious individuals and organizations accept evolution as a scientific explanation for the diversity of life

Frequently Asked Questions

What is AP Bio Unit 7 about?

Unit 7 is Natural Selection — the AP Bio unit on mechanisms and evidence of evolution. It walks through natural and artificial selection, population genetics, Hardy–Weinberg equilibrium, phylogeny and speciation, evidence for common ancestry, continuing evolution (like antibiotic resistance), and origins of life. You’ll focus on how allele frequencies change and how to use tools like cladograms and Hardy–Weinberg models to analyze populations. Expect about 13–20% of the exam weight and roughly 19–21 class periods of content. For details and Fiveable’s official study guide, check the unit page (https://library.fiveable.me/ap-bio/unit-7). For focused practice, Fiveable also has cheatsheets, cram videos, and 1000+ practice items in the practice bank (https://library.fiveable.me/practice/bio).

What topics are covered in AP Bio Unit 7 (Natural Selection)?

You’ll find the full Unit 7 topic list at https://library.fiveable.me/ap-bio/unit-7. The unit covers topics 7.1–7.12: Introduction to Natural Selection. Natural Selection. Artificial Selection. Population Genetics. Hardy‑Weinberg Equilibrium (including p/q and p2+2pq+q2). Evidence of Evolution. Common Ancestry. Continuing Evolution (resistance and emergent diseases). Phylogeny (trees and cladograms). Speciation (allopatric/sympatric, isolating mechanisms, rates). Variations in Populations (genetic diversity, bottlenecks, founder effect). Origins of Life on Earth (RNA world hypothesis and early fossil dates). These align with the CED and make up about 13–20% of the AP exam. For concise review, Fiveable’s Unit 7 study guide, cheatsheets, cram videos, and practice questions are available at the same link.

How much of the AP Biology exam is Unit 7?

About 13–20% of the AP Biology exam focuses on Unit 7 (Natural Selection). The unit includes natural and artificial selection, population genetics, Hardy–Weinberg calculations, phylogeny, speciation, and evidence for evolution. It’s usually taught over roughly 19–21 class periods. On the test you’ll see both multiple-choice and free-response items tied to these concepts, so practice interpreting data, doing Hardy–Weinberg math, and explaining evolutionary mechanisms clearly. For a focused review, Fiveable’s Unit 7 study guide, cheatsheets, and cram videos can help (https://library.fiveable.me/ap-bio/unit-7). Use practice questions to build speed and accuracy before test day.

What's the hardest part of AP Bio Unit 7?

Students often struggle with applying Hardy–Weinberg math and tying population-genetics concepts to natural selection (see Unit 7 at https://library.fiveable.me/ap-bio/unit-7). Many understand selection in words but trip up on setting up HWE problems, calculating genotype and allele frequencies, knowing when HWE assumptions are violated, and interpreting how selection, drift, migration, and nonrandom mating change frequencies. Translating phylogeny and speciation ideas into evidence-based FRQ explanations (like reproductive isolation mechanisms and branching patterns) is also tricky. Practice timed HWE calculations and use stepwise reasoning for selection and phylogeny problems to build speed and accuracy. Fiveable’s study guide, cheatsheets, and practice questions target those exact pain points.

How should I study for AP Bio Unit 7 (study guide, Quizlet, and practice FRQs)?

Yes — start with a Quizlet set (try “AP Bio Evolution Terms”) to drill vocabulary and core concepts fast. Then work through the Unit 7 study guide to learn ideas in order: natural selection, Hardy‑Weinberg, phylogeny, speciation, and evidence of evolution (https://library.fiveable.me/ap-bio/unit-7). After that, do targeted practice FRQs: pick 4–6 past evolution FRQs, time yourself, grade with College Board rubrics, then redo missed parts. Spend extra time on Hardy‑Weinberg and chi‑square — aim for at least 8–10 problems. Finish with mixed practice questions to simulate exam retrieval. For concise review and extra practice, Fiveable’s cram videos and practice bank are solid resources (https://library.fiveable.me/practice/bio).