7.8 Continuing Evolution

“Continuing evolution” is just the AP way of saying evolution never stops—species have changed in the past and they’re still changing now. It’s the same process as regular evolution (mutations, standing genetic variation, natural selection, gene flow, horizontal gene transfer) but highlighted with modern, observable examples: genomic changes over time, transitional fossils, antibiotic/pesticide/herbicide/chemotherapy resistance, and pathogens showing antigenic drift/shift that cause new diseases (LO 7.8.A; EK 7.8.A.1). On the exam you should be able to explain ongoing change using specific selective pressures and mechanisms (e.g., antibiotic use selects resistant alleles; viruses evolve via antigenic drift). For a focused review, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7). Practice applying these examples with 1000+ AP-style problems (https://library.fiveable.me/practice/ap-biology).

Bacteria become resistant quickly because evolution acts fast in huge populations. Random genomic mutations (or existing standing genetic variation) sometimes change a protein or pump so an antibiotic no longer works. Bacteria also exchange resistance genes by horizontal gene transfer (conjugation, transformation, transduction), spreading useful alleles between strains and species. Strong selective pressure from antibiotic use means susceptible cells die and resistant ones reproduce—because bacteria can divide every 20 minutes, resistant alleles can rise to high frequency in days to weeks. This is exactly EK 7.8.A.1(iii): evolution of antibiotic resistance as ongoing evolution. On the AP exam you should link mutation/HGT + selection and population size/generation time when explaining resistance. For a quick review, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and try practice questions at (https://library.fiveable.me/practice/ap-biology).

Short answer: evolution is happening now because we can measure heritable genomic changes and see natural selection change allele frequencies in real time. How scientists know (examples tied to LO 7.8.A/EK 7.8.A.1): - Direct genomic evidence: sequencing shows mutations and changing allele frequencies across generations (genomic mutations, standing genetic variation). - Observed microevolution: antibiotic-, pesticide-, herbicide-, and chemotherapy-resistance evolve quickly when those drugs/herbicides create selective pressure (antibiotic resistance, pesticide resistance). - Pathogens change: influenza and HIV show antigenic drift/shift and new emergent diseases as their genomes change. - Experimental/field data: lab evolution (e.g., Lenski’s E. coli) and field studies (mosquito insecticide resistance) document fitness changes over years. - Fossil + transitional forms show continuous change over deep time, so evolution is ongoing. On the AP exam you might be asked to explain mechanisms (mutation, selection, horizontal gene transfer) and use data to support claims—so practice interpreting allele-frequency or mortality graphs. For a focused review, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP), the whole Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and >1,000 practice problems (https://library.fiveable.me/practice/ap-biology).

Short answer: the process is the same (mutation + variation + selection + drift + gene flow), but what differs is timescale, evidence, and how we detect it. Millions-of-years evolution is inferred from the fossil record, transitional fossils, comparative anatomy and genomics showing deep genomic changes and adaptive radiations. Recent/ongoing evolution is observed directly—e.g., antibiotic, pesticide, herbicide, chemotherapy resistance; pathogens changing by antigenic drift/shift; or rapid genomic changes via horizontal gene transfer. Key differences: - Timescale: deep-time changes accumulate over millions of years; contemporary changes can happen in years or even days. - Evidence: fossils and phylogenies vs. real-time allele-frequency shifts, lab/field experiments, and genomic sequencing. - Agents: long-term environmental shifts vs. modern selective pressures (drugs, agriculture, climate, human movement). For AP: connect this to LO 7.8.A and EKs (genomic mutations, standing genetic variation, selective pressure). Want practice? Check the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7). For extra practice problems see (https://library.fiveable.me/practice/ap-biology).

Short answer: pathogens don’t “stay the same”—they keep evolving because their genomes change and selection favors variants that survive treatments or immune responses. Mutations (random DNA changes), recombination, and horizontal gene transfer (bacteria swapping plasmids) create genetic variation. Because bacteria and viruses reproduce fast and in huge numbers, beneficial changes (like an antibiotic-resistance gene or a change in a viral surface protein) can spread in days to years under selective pressure (drug use, vaccines, hosts’ immunity). Examples that match the AP CED: antibiotic resistance, pesticide/herbicide resistance, antigenic drift and antigenic shift in influenza, and emergent diseases (EK 7.8.A.1 iii–iv; LO 7.8.A). On the AP exam you might be asked to explain mechanisms (mutations, selection, HGT) and give evidence—so practice describing genomic changes and selective pressures. Review Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and try practice problems (https://library.fiveable.me/practice/ap-biology) to get comfy with these examples.

Genomic changes over time are just changes in DNA that build up in populations. They start with mutations (random changes in genes) and with standing genetic variation already in a population. Some changes spread because they help organisms survive or reproduce under a selective pressure (natural selection)—for example, alleles for antibiotic, pesticide, herbicide, or chemotherapy resistance become common when those chemicals are used. Other changes spread by chance (genetic drift) or by gene flow (immigration) and sometimes by horizontal gene transfer (common in bacteria). Pathogens also change their genomes continuously (antigenic drift and occasional antigenic shift), which leads to emergent diseases. The CED calls this LO 7.8.A: evolution is ongoing—look for examples like resistance and fossil/transitional records on the exam. For a focused review and AP-style examples, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and practice questions (https://library.fiveable.me/practice/ap-biology).

You need to worry because pesticide resistance is a real, ongoing example of natural selection (EK 7.8.A.1.iii). Random genomic changes (mutations) or standing genetic variation can produce alleles that reduce insect sensitivity to a pesticide. When farmers spray, that creates strong selective pressure: susceptible insects die and resistant ones survive and reproduce, so resistance alleles increase in frequency. That makes control less effective, so people use more or stronger pesticides, raising costs, harming non-target species, and increasing environmental and human health risks. For disease vectors (like mosquitoes), resistance can cause failure of public-health measures and more disease transmission. The AP exam often asks you to explain mechanisms (mutations, selection, allele frequency change) and interpret data (see LO 7.8.A and Unit 7 content); practicing these skills helps for multiple-choice and FRQs. For a quick topic review, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice questions (https://library.fiveable.me/practice/ap-biology).

The fossil record shows evolution is continuous by preserving a sequence of forms through time—including transitional fossils that bridge major groups (e.g., fish → tetrapods, or feathered dinosaurs → birds). As you move up the rock layers (older → younger), you see gradual anatomical changes that match predictions from descent with modification: homologous structures shifting, new traits appearing and diversifying, and adaptive radiations after mass extinctions. That continuous change in fossils is one line of evidence (EK 7.8.A.1.ii) that, together with genomic change and observed resistance evolution, shows species keep evolving. For AP-style answers, cite specific fossil transitions and explain how stratigraphic order provides temporal context—use evidence + reasoning to support the claim (science practice 6). Want a quick review and examples you can use on the exam? Check the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP). For extra practice, try problems at (https://library.fiveable.me/practice/ap-biology).

Use these clear, current examples on an FRQ—name the species, selective pressure, mechanism, and expected data pattern: - Antibiotic resistance in bacteria (MRSA, E. coli): selective pressure = antibiotics; mechanisms = genomic mutations and horizontal gene transfer; prediction = rising resistant-allele frequency and treatment failures. - Mosquitoes (Anopheles gambiae) evolving pyrethroid resistance (kdr mutation): selective pressure = insecticide-treated nets; mechanism = point mutation in sodium channel (LO 7.8.A; selective pressure/natural selection); prediction = higher survival and increased resistant-allele frequency. - Herbicide-resistant weeds (Palmer amaranth): pressure = glyphosate use; mechanism = gene amplification/mutations; prediction = weed survival in treated fields. - Viruses: influenza antigenic drift/shift and SARS-CoV-2 variants—pressure = host immunity/vaccination; mechanism = rapid mutation; prediction = emergent strains and reduced vaccine effectiveness. On the exam, state the selective pressure, genetic change (mutation, HGT, standing variation), how selection changes allele frequencies, and cite expected data (mortality/survival, allele-frequency tables, time series). For a quick refresher, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and more practice at (https://library.fiveable.me/practice/ap-biology).

Cancer cells become resistant to chemotherapy by evolving under strong selective pressure. Tumors are genetically diverse (standing genetic variation); chemo kills sensitive cells, leaving rare cells with mutations that let them survive. Those mutations can change the drug’s target, increase drug efflux pumps, boost DNA repair, inactivate the drug, or block apoptosis—so resistant clones expand (natural selection). New resistance can also arise by further mutations during treatment (genomic mutations) or by selection of preexisting resistant clones. Clinically this looks like initial shrinkage then relapse with a resistant tumor. This is exactly the “evolution of resistance” example in the AP CED (LO 7.8.A, EK 7.8.A.1.iii). For a quick AP-aligned review, check the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and practice problems (https://library.fiveable.me/practice/ap-biology).

Evolution can be very fast—from hours or days in microbes to years or decades in animals. Bacteria and viruses evolve quickest: high mutation rates, short generation times, and horizontal gene transfer let antibiotic or antiviral resistance appear in days–months (EK 7.8.A.1, iii–iv). Insects (like mosquitoes) can evolve pesticide resistance over a few years when strong selective pressure exists. Larger animals with longer generations (mammals, trees) usually change over many generations—often decades to millennia—though noticeable shifts (behavior, timing, host use) can show up in decades. Key drivers are mutations, standing genetic variation, natural selection, and selective pressure; horizontal gene transfer speeds change in microbes. For AP Bio, know these examples (antibiotic/pesticide resistance, pathogen antigenic drift/shift) and tie them to LO 7.8.A. For more examples and exam-style practice, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7). For extra practice, try the 1000+ questions (https://library.fiveable.me/practice/ap-biology).

Emergent diseases are a clear example of evolution happening right now. Pathogens (viruses, bacteria, parasites) accumulate genomic mutations and sometimes swap genes horizontally; most changes are neutral, but some change traits that affect survival in hosts or under drugs. When a population is exposed to a selective pressure—antibiotics, vaccines, new host species—variants that survive reproduce more, so resistance or new host-range traits increase in frequency (EK 7.8.A.1 iii–iv, LO 7.8.A). Think antigenic drift (small, continual viral changes) and antigenic shift (big reassortments—e.g., influenza) or bacteria gaining antibiotic-resistance genes. Zoonotic jumps (animal → human) are another path for emergent disease as pathogens adapt to a new host. On the AP exam, expect questions tying mutations, natural selection, and horizontal gene transfer to real cases of resistance or disease emergence (Unit 7: Natural Selection). For more review, see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and extra practice (https://library.fiveable.me/practice/ap-biology).

Antibiotic resistance is a clear example of natural selection in action. Random genomic mutations or horizontally transferred genes can give some bacteria alleles that make them less affected by an antibiotic (standing genetic variation or new mutations). When an antibiotic is used, that drug becomes a selective pressure: susceptible bacteria die, resistant ones survive and reproduce, so the frequency of resistance alleles increases in the population over time. This fits EK 7.8.A.1.iii (evolution of resistance). On the AP exam you should link mutation/variation → selective pressure → differential survival/reproduction → change in allele frequency (use those CED terms). For more examples and test-style explanations see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and the unit overview (https://library.fiveable.me/ap-biology/unit-7). Want practice questions? Try the 1,000+ AP practice problems here (https://library.fiveable.me/practice/ap-biology).

Herbicide-resistant weeds evolve by natural selection. Rare genetic changes (new mutations or standing genetic variation) make some plants less affected by a herbicide. When farmers spray that herbicide, they create a strong selective pressure: susceptible plants die and resistant ones survive and reproduce, so the resistance allele increases in frequency over generations. Gene flow (seeds/pollen moving) can spread resistance between fields, too. This matters for farmers because resistant weeds reduce crop yields, force higher costs (more or different herbicides, extra labor), and can require more complex management (crop rotation, mechanical weeding). On the AP Bio exam this is a classic LO 7.8.A example of continuing evolution—EK 7.8.A.1.iii—and you should be ready to connect mutations, selection, and changing allele frequencies. For a quick review see the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice questions (https://library.fiveable.me/practice/ap-biology).

Yes—humans are still evolving. Evolution is ongoing whenever genomic mutations, standing genetic variation, gene flow, genetic drift, and selection change allele frequencies over time (EK 7.8.A.1). Technology (medicine, sanitation, contraception) has relaxed some selective pressures (fewer deaths from infection), but it also creates new ones (antibiotic/antiviral resistance, changes in fertility patterns, lifestyle-related selection). Examples: past and recent changes like lactase persistence, sickle-cell malaria resistance, and shifts in pathogen genes show evolution continues. Cultural niche construction and migration change gene flow and selective environments, so allele frequencies can shift even without classical “natural” selection. For the AP exam, be ready to explain mechanisms (mutation, selection, drift, gene flow) and give real examples (antibiotic resistance, antigenic drift/shift) as evidence that evolution is ongoing. For a quick review, check the Topic 7.8 study guide (https://library.fiveable.me/ap-biology/unit-7/continuing-evolution/study-guide/fb67fTvqhnbBXkLYOazP) and more practice at (https://library.fiveable.me/practice/ap-biology).