How do we know evolution is still happening today?
Topic 7.8 Continuing Evolution: explain how ongoing examples such as antibiotic resistance and pesticide resistance show that evolution continues.
A focused answer to AP Biology Topic 7.8, covering observable, ongoing evolution including antibiotic and pesticide resistance, emerging diseases, and how these illustrate natural selection in real time, with a worked example.
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What this topic is asking
The College Board (Topic 7.8) wants you to explain that evolution is ongoing and observable, using examples such as antibiotic resistance, pesticide resistance and emerging diseases, and to apply natural selection to these real-time cases.
Evolution is observable now
Antibiotic resistance
Why incomplete treatment is dangerous
The same logic explains why overusing antibiotics in medicine and agriculture has produced multi-drug-resistant bacteria, one of the most serious public-health problems of our time. It is a direct, observable consequence of natural selection, and understanding it is exactly why the AP course treats ongoing evolution as evidence and as an applied problem.
Try this
Q1. State where resistance alleles come from relative to the antibiotic. [1 point]
- Cue. They arise by random mutation before the antibiotic is applied; the antibiotic selects for them, it does not create them.
Q2. Explain why bacteria evolve resistance faster than large animals. [2 points]
- Cue. Bacteria have very short generation times and huge populations, so mutations arise often and selection acts over many generations quickly, allowing rapid evolution.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2021 (style)4 marksSection II (long FRQ excerpt). A population of bacteria is repeatedly treated with an antibiotic, and over time the antibiotic stops working. (a) Explain how antibiotic resistance evolves in the bacterial population. (b) Explain why finishing a full course of antibiotics, rather than stopping early, reduces the spread of resistance.Show worked answer →
A 4-point explain FRQ on antibiotic resistance.
(a) Explain (2 points): (1 point) the bacterial population already varies, and a few cells carry a mutation giving resistance; (1 point) the antibiotic kills the non-resistant cells, so the resistant cells survive and reproduce, passing on the resistance allele, and over generations resistant bacteria dominate.
(b) Explain (2 points): (1 point) finishing the course kills the partially resistant bacteria that survive the early doses; (1 point) stopping early leaves these survivors to reproduce, increasing the frequency of resistance alleles and spreading resistance.
Markers reward describing selection of pre-existing resistant variants and explaining why incomplete treatment selects for resistance.
AP 2018 (style)1 marksSection I (multiple choice). Antibiotic resistance spreads in a bacterial population mainly because antibiotics: (A) cause bacteria to mutate on purpose. (B) select for pre-existing resistant variants that survive and reproduce. (C) make all bacteria resistant. (D) increase the bacterial reproduction rate.Show worked answer →
The correct answer is (B).
Resistance alleles arise by random mutation before the antibiotic is applied; the antibiotic then selects for these pre-existing resistant variants by killing the others. The antibiotic does not direct mutations (A), make all bacteria resistant (C), or speed reproduction (D).
Related dot points
- Topic 7.1 Introduction to Natural Selection: explain the conditions required for natural selection and how it leads to changes in a population.
A focused answer to AP Biology Topic 7.1, covering Darwin's reasoning, the conditions for natural selection (variation, heritability, overproduction, differential reproduction), fitness, and how selection changes allele frequencies, with a worked example.
- Topic 7.2 Natural Selection: explain how directional, stabilizing and disruptive selection change the distribution of phenotypes in a population.
A focused answer to AP Biology Topic 7.2, covering directional, stabilizing and disruptive selection, sexual selection, and how each changes a phenotype distribution, with a worked interpretation of selection on a trait.
- Topic 7.4 Population Genetics: explain how natural selection, mutation, gene flow, genetic drift and non-random mating change allele frequencies.
A focused answer to AP Biology Topic 7.4, covering the gene pool, allele frequencies, and the five mechanisms of microevolution (selection, mutation, gene flow, genetic drift, non-random mating), including bottleneck and founder effects, with a worked allele-frequency calculation.
- Topic 6.7 Mutations: explain the types of mutations and how they affect gene products, phenotype and the variation available to a population.
A focused answer to AP Biology Topic 6.7, covering point mutations (silent, missense, nonsense), frameshift mutations, chromosomal mutations, their effects on proteins and phenotype, and their role as the source of new variation, with a worked example.
- Topic 7.6 Evidence of Evolution: describe the lines of evidence (fossil, anatomical, molecular, biogeographical) that support evolution.
A focused answer to AP Biology Topic 7.6, covering fossil, anatomical (homologous and vestigial structures), embryological, molecular and biogeographical evidence for evolution, with a worked interpretation of molecular data.
Sources & how we know this
- AP Biology Course and Exam Description — College Board (2020)