What conditions are required for natural selection, and how does it drive evolution?
Describe the conditions required for natural selection, including overproduction of offspring, inherited variation, and the struggle to survive, that result in differential reproductive success (NGSSS SC.912.L.15.13; Reporting Category 2, Classification, Heredity, and Evolution).
A benchmark-level answer on natural selection for the Florida Biology 1 EOC: overproduction, inherited variation, the struggle to survive, differential reproductive success, adaptation, and worked examples like antibiotic resistance.
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What this topic is asking
The NGSSS benchmark SC.912.L.15.13 asks you to describe the conditions required for natural selection: overproduction of offspring, inherited variation, and a struggle to survive, leading to differential reproductive success. For the Florida Biology 1 EOC you must be able to lay out these conditions and apply them to a scenario (camouflage, antibiotic resistance, beak shape). The most-tested idea is that natural selection acts on existing inherited variation, the environment does not create traits to order.
The conditions for natural selection
The result, over many generations, is that the helpful inherited traits become more common and the population becomes better adapted.
Variation, fitness, and adaptation
The key point the EOC tests: natural selection works on variation that is already present in the population (which comes from mutation and from the shuffling in meiosis). The environment does not produce a new trait because it is needed; it selects among the variations that already exist. Organisms also do not choose their traits or change themselves to fit, a very common misconception.
How natural selection drives evolution
Putting it together: a population has variation; more offspring are born than can survive; those with favorable inherited traits survive and reproduce more; so the favorable traits become more common over generations. This shift in the population's inherited traits over time is evolution. Given enough time and isolation, accumulated changes can lead to new species.
A clean example is antibiotic resistance: a few bacteria already carry a resistance trait, the antibiotic kills the non-resistant bacteria (a selection pressure), and the resistant ones survive and multiply, so the population becomes resistant. The antibiotic did not create resistance; it selected for the bacteria that already had it.
Try this
Q1. State the four conditions required for natural selection. [2]
- Cue. Overproduction of offspring; inherited variation; a struggle to survive (limited resources); differential reproductive success (favorable traits reproduce more).
Q2. Explain why antibiotic resistance spreads in a bacterial population. [2]
- Cue. A few bacteria already carry resistance; the antibiotic kills the non-resistant bacteria, so the resistant ones survive and reproduce, making resistance common.
Exam-style practice questions
Practice questions written in the style of FLDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
FL Biology 1 EOC (2023 released style)1 marksIn a population of beetles, green beetles are better camouflaged than brown beetles and are eaten by birds less often. Over many generations, the population becomes mostly green. Which process explains this change? (A) The beetles chose to turn green. (B) Natural selection: better-camouflaged beetles survive and reproduce more. (C) The brown beetles changed into green beetles. (D) The change is random and not inherited.Show worked answer →
A 1-point multiple-choice item on natural selection.
The correct answer is B. Green beetles have a survival advantage (camouflage), so they survive and reproduce more, passing on the green trait. Over generations the population shifts toward green. Organisms do not choose their traits (A) or transform individually (C), and the change is inherited and non-random in effect (D).
Natural selection acts on existing inherited variation; the better-suited variant reproduces more.
FL Biology 1 EOC (2024 released style)1 marksA doctor warns that overusing antibiotics leads to resistant bacteria. Using natural selection, why does antibiotic resistance spread in a bacterial population? (A) Antibiotics teach bacteria to resist. (B) A few bacteria already have resistance; the antibiotic kills the rest, so the resistant ones survive and reproduce. (C) All bacteria become resistant at once. (D) Bacteria decide to resist the drug.Show worked answer →
A 1-point item applying natural selection to antibiotic resistance.
The correct answer is B. Variation already exists: a few bacteria carry a resistance trait. The antibiotic kills the non-resistant bacteria (selection pressure), so the resistant ones survive and reproduce, and resistance becomes common. The antibiotic does not create or teach resistance (A and D), and resistance does not appear in all at once (C).
Related dot points
- Discuss mechanisms of evolutionary change other than natural selection, including genetic drift, gene flow, non-random mating, and mutation (NGSSS SC.912.L.15.14; Reporting Category 2, Classification, Heredity, and Evolution).
A benchmark-level answer on the other mechanisms of evolution for the Florida Biology 1 EOC: genetic drift (including the bottleneck and founder effects), gene flow, non-random mating, and mutation, and how each changes a population's gene pool.
- Explain how the scientific theory of evolution is supported by the fossil record, comparative anatomy, comparative embryology, biogeography, molecular biology, and observed evolutionary change (NGSSS SC.912.L.15.1; Reporting Category 2, Classification, Heredity, and Evolution).
A benchmark-level answer on the evidence for evolution for the Florida Biology 1 EOC: the fossil record, comparative anatomy (homologous structures), comparative embryology, biogeography, molecular biology, and observed change.
- Describe how mutation and genetic recombination increase genetic variation, and the possible effects of mutations (NGSSS SC.912.L.15.15; Reporting Category 2, Classification, Heredity, and Evolution).
A benchmark-level answer on mutation and variation for the Florida Biology 1 EOC: types of mutations, harmful, neutral, and beneficial effects, genetic recombination through meiosis and fertilization, and why variation matters for evolution.
- Discuss the distinguishing characteristics of the domains and kingdoms of living organisms, and explain how and why organisms are hierarchically classified by evolutionary relationships (NGSSS SC.912.L.15.6 and SC.912.L.15.4; Reporting Category 2, Classification, Heredity, and Evolution).
A benchmark-level answer on classification for the Florida Biology 1 EOC: the three domains and six kingdoms, the taxonomic hierarchy, binomial nomenclature, and why classification is based on evolutionary relationships and can change.
- Analyze how population size is determined by births, deaths, immigration, and emigration, and how limiting factors (biotic and abiotic) determine the carrying capacity of an environment (NGSSS SC.912.L.17.5; Reporting Category 3, Organisms, Populations, and Ecosystems).
A benchmark-level answer on population dynamics for the Florida Biology 1 EOC: how births, deaths, immigration, and emigration change population size, limiting factors, carrying capacity, and exponential versus logistic growth.
Sources & how we know this
- Next Generation Sunshine State Standards: Science (Biology 1) — Florida Department of Education (2024)
- Biology 1 End-of-Course Assessment Test Item Specifications — Florida Department of Education (2024)