Biological Evolution Practice
Unit: Biological Evolution - Practice (Lessons 2-4)
Learning Objectives
Apply concepts of superposition, dating methods, and index fossils to interpret geological evidence
Explain how natural selection drives population change through overproduction, variation, selection, and inheritance
Distinguish adaptation types and explain how geographic isolation leads to speciation
Introduction
~1 minutesBiological Evolution Practice
This practice covers three key topics from the Biological Evolution unit. Each section includes a brief review of core concepts followed by questions to test your understanding.
Use this practice to identify what you know well and where you may need to review.
Review: Reading the Rock Record
~3 minutesSection 1: Reading the Rock Record
Earth's history is recorded in layers of sedimentary rock. The Law of Superposition tells us that in undisturbed rock layers, the oldest layers are on the bottom and the youngest are on top. Scientists use relative dating to determine which rocks are older or younger without knowing exact ages, and absolute dating (radiometric dating) to calculate a rock's actual age in years by measuring radioactive decay and half-lives.
Index fossils are remains of organisms that lived for a short time but were widespread geographically. Finding the same index fossil in rock layers at different locations means those layers are approximately the same age, a process called correlation. The geologic time scale organizes Earth's 4.6-billion-year history into eons, eras, periods, and epochs, with boundaries defined by major events like mass extinctions. Additional geological evidence comes from ice cores (which preserve ancient atmospheric samples), faults (cracks where rock shifted), and igneous intrusions (hardened magma that cuts through existing rock).
Law of Superposition: in undisturbed layers, the oldest are on the bottom. Relative dating: determining which rocks are older or younger without exact ages. Absolute dating (radiometric dating): calculating exact age using radioactive decay. Half-life: the time for half of the parent atoms to decay into daughter atoms. Index fossil: a widespread, short-lived organism's fossil used as a time marker. Correlation: matching rock layers across locations using shared fossils. Geologic time scale: the organized timeline of Earth's history (eons, eras, periods, epochs). Unconformity: a gap in the rock record where layers are missing.
Practice: Reading the Rock Record
A geologist discovers five undisturbed sedimentary rock layers at a cliff. She finds a trilobite fossil in the second layer from the bottom and a fern fossil in the fourth layer from the bottom. Which conclusion is best supported by this evidence?
Carbon-14 dating can be used to determine the age of a dinosaur bone that is 70 million years old.
A radioactive element has a half-life of 200 million years. A rock sample originally contained 800 parent atoms of this element, and now contains only 100 parent atoms. How old is the rock?
A gap in the rock record where layers are missing due to erosion or a pause in deposition is called a(n) ______.
Which of the following are types of evidence geologists use to reconstruct Earth's history? (Select all that apply)
Select all that apply.
Review: Natural Selection
~3 minutesSection 2: Natural Selection
Natural selection is the mechanism that drives evolution. It requires four conditions working together. Overproduction: organisms produce far more offspring than can survive, creating competition for limited resources. Variation: individuals in a population differ in their traits. Selection: individuals with traits better suited to the environment survive and reproduce at higher rates (differential survival). Inheritance: advantageous traits are passed to offspring through genes.
Over many generations, beneficial traits become more common and the population evolves. Genetic variation, the raw material for natural selection, comes from three sources: mutations (random DNA changes, the only source of entirely new genetic material), sexual reproduction (meiosis shuffles existing genes into new combinations), and gene flow (migration introduces new alleles between populations). In biology, fitness does not mean physical strength. It means how well an organism is suited to survive and reproduce in its specific environment.
Natural selection: the process by which organisms with advantageous traits survive and reproduce more, changing the population over generations. Overproduction: producing more offspring than can survive. Variation: differences in traits among individuals in a population. Fitness: how well an organism is suited to survive and reproduce in its specific environment. Genetic variation: differences in DNA among individuals. Mutation: a random change in DNA; the only source of brand-new genetic material. Gene flow: movement of alleles between populations through migration. Allele: a version of a gene.
Practice: Natural Selection
A species of frog produces 2,000 eggs per year, but only about 20 survive to adulthood. Which principle of natural selection does this best illustrate?
A cheetah that exercises daily will pass its increased speed to its offspring through its genes.
During a severe drought, a population of wildflowers with deeper root systems survives while those with shallow roots die. The surviving plants reproduce and pass the deep-root trait to their offspring. Over many generations, deep roots become the norm. Which statement best describes what happened?
Sexual reproduction and gene flow can shuffle and move existing genes, but ______ are the only source of entirely new genetic material.
Match each scenario to the principle of natural selection it primarily demonstrates.
Review: Adaptation and Speciation
~3 minutesSection 3: Adaptation and Speciation
An adaptation is an inherited trait that increases an organism's ability to survive and reproduce. Adaptations come in three types. Structural adaptations are physical body features (polar bear fur, cactus spines, webbed feet). Behavioral adaptations are inherited actions (migration, hibernation, pack hunting). Physiological adaptations are internal body processes (venom production, antifreeze proteins, efficient kidneys).
Natural selection reshapes populations in three patterns. Directional selection favors one extreme of a trait, shifting the population in that direction (peppered moths darkening during industrial pollution). Stabilizing selection favors the average and reduces variation (human birth weight clustering around a healthy middle). Disruptive selection favors both extremes over the middle, potentially splitting the population (seed-cracker finch beaks diverging into large and small sizes). Speciation most commonly occurs through geographic isolation: a physical barrier divides a population, gene flow stops, different selection pressures cause each group to diverge genetically, and eventually the groups can no longer interbreed. They have become separate species.
Adaptation: an inherited trait that helps an organism survive and reproduce. Structural adaptation: a physical body feature. Behavioral adaptation: an inherited action or behavior. Physiological adaptation: an internal body process. Directional selection: favors one extreme, shifts the population. Stabilizing selection: favors the average, narrows variation. Disruptive selection: favors both extremes, can split the population. Speciation: the formation of new species from an existing population. Geographic isolation: a physical barrier separating a population and stopping gene flow. Reproductive isolation: when populations can no longer interbreed and produce fertile offspring.
Practice: Adaptation and Speciation
A desert lizard avoids the hottest part of the day by burrowing underground and emerging only at dawn and dusk. What type of adaptation is this?
In a population of rabbits, individuals with average-sized ears survive best. Rabbits with very large ears lose too much body heat in winter, and rabbits with very small ears overheat in summer. Over time, ear size in the population becomes less variable and clusters around the average. What type of selection is this?
A mountain range rises and divides a population of mice into eastern and western groups. Over thousands of generations, the two groups become separate species. Which factors contributed to this speciation? (Select all that apply)
Select all that apply.
A river forms and divides a single bird species into two isolated populations. Arrange the following events in the order they would occur during the speciation process.
Disruptive selection favors individuals with average trait values and reduces variation in the population.