Unit 05 · Evolution & Adaptation
Living things fit their homes in amazing ways — a polar bear’s thick fur, a cactus’s spines. This unit explains how those adaptations come to be. You’ll see how differences within a species, plus survival and reproduction, add up to natural selection over very long times, and how fossils give us evidence. Mastery means you can explain how a species changes over time — and why evolution is a branching tree, not a ladder.
Student learning: When can a change in a population support natural selection?
Choose the level by readiness, not age alone, and record it before instruction. Foundation, core, and honors tasks are study pathways, not an AP course or a promise of college credit. The instructor retains practical assessment and the published science rubric; integration is reported separately.
Prerequisites: Variation, inheritance, counts and percentages; distinguish an individual from a population.
Suggested sequence: read and discuss the explanation; attempt the worked model; analyze the data at your selected level; check the answers; then complete the source-linked response and a fresh transfer question. These activities supplement, not replace, supervised practical work and the full-year schedule.
Assigned reading and focus
- OpenStax Biology 2e, 18.1: Understanding Evolution. Read Charles Darwin and Natural Selection, Evidence of Evolution, and Misconceptions of Evolution. Mark Darwin and Wallace's 1858 presentation and Darwin's 1859 book; compare fossils and anatomical evidence with the finch example. Checked 2026-09-27.
- OpenStax Biology 2e, 20.1: Organizing Life on Earth. Read Phylogenetic Trees, Limitations of Phylogenetic Trees, and Classification Levels; examine Figures 20.4-20.6. Distinguish a branching ancestry hypothesis from a practical identification key. Checked 2026-09-27.
Learn the science
Natural selection requires pre-existing heritable variation and differences in reproductive success in a particular environment. Individuals do not acquire a needed beak by deciding to adapt; population frequencies can change across generations.
Darwin and Wallace presented explanations in 1858; Darwin published On the Origin of Species in 1859. Later observations and experiments test the mechanisms. A classroom model illustrates an argument but is not their field record or the Grants' measurements.
Fossils, anatomical comparisons and molecular evidence can support a branching tree of relationships. Similar-looking features do not automatically prove recent common ancestry, and living species are not rungs on a ladder toward humans.
In the deliberately simplified model, beak category is inherited unchanged, no individuals migrate, and every survivor contributes two offspring. The assigned survival rule is a model assumption, not evidence that all deep beaks are always better.
Data, provenance, and assumptions
| Environment | Inherited beak category | Starting birds | Survivors | Offspring per survivor |
|---|---|---|---|---|
| Hard seeds | Shallow | 32 | 8 | 2 |
| Hard seeds | Deep | 32 | 24 | 2 |
| Soft seeds | Shallow | 32 | 24 | 2 |
| Soft seeds | Deep | 32 | 8 | 2 |
Paper-model procedure: one generation in each environment
Scope and safety: Use paper labels or drawn tally boxes only. The seed types are words on cards, not food to handle or eat.
Materials and preparation
- A sheet with 32 tally boxes for each beak category, pencil, and the supplied survival rule table.
- Two record columns labeled starting generation and offspring generation; keep the environments separate.
Procedure and schedule
- Mark the 32 starting individuals of each type for the hard-seed environment.
- Apply the listed survival counts, retaining survivors as a separate count rather than relabeling individuals.
- Record two offspring per survivor, retire the starting generation, and calculate offspring frequencies.
- Reset to the original 32/32 for the soft-seed environment and repeat. Record each round and rule; do not describe the result as an observation of living birds.
Record: Environment, starting counts, survivors, offspring counts, denominators, frequencies, and the rule applied. If you only analyze the supplied table, label it supplied-data analysis; the instructor separately observes any model-running skill.
Worked model
In hard seeds, shallow survival is 8/32 = 25% and deep survival is 24/32 = 75%. Offspring are 16 shallow and 48 deep, so deep beaks change from 50% to 48/64 = 75% of the next generation. Survival probability and next-generation frequency happen to match numerically here, but use different denominators.
Numerical calibration
- 75 % of initial deep-beak birds surviving in hard seeds
- 75 % deep-beak offspring under two offspring per survivor
Attempt the assigned level
Try the tasks before reading the calibration. These are practice answers, not a secure examination; use a new dataset or changed assumption for the assessed transfer.
Foundation: typically grades 7-8
- Draw a before/after bar chart of the hard-seed population and label survivors separately from offspring.
- Use one fossil or anatomical example in the assigned reading to explain a branch on a tree; state why "more evolved" is not a rank for living species.
Check after your attempt
- Starting 32/32; survivors 8/24; offspring 16/48. No individual changes beak category in this model.
- Accept a cited example with shared ancestry and a limitation; a branching tree records relationships, not a ladder of worth or progress.
High-school core: typically grades 9-10
- Calculate survival percentages and next-generation frequencies in both environments. Explain the role of inheritance and reproduction.
- Give an alternative explanation for a changed trait frequency in a real small population, such as migration or chance, and identify data needed to distinguish it.
Check after your attempt
- Hard: 25%/75% survival, offspring 25% shallow and 75% deep. Soft: 75%/25% survival, offspring 75% shallow and 25% deep.
- Track parent/offspring traits, survival, reproductive output, migration and repeated populations; a frequency shift alone is not a unique signature of selection.
Honors extension: typically grades 11-12
- Keep hard-seed survivor counts but let each shallow survivor contribute four offspring and each deep survivor one. Recalculate deep-beak frequency.
- Explain why a conclusion based only on survival can miss the selection outcome, even if survival counts are accurate.
Check after your attempt
- 32 shallow and 24 deep offspring: 24/56 = 42.86% deep, lower than the original 50%.
- Reproductive success includes offspring contributions, not survival alone. The changed reproduction assumption reverses the directional prediction.
History, reading, and writing connection
Original response: Write a six-sentence explanation comparing Darwin and Wallace's 1858 idea, a specific evidence example in OpenStax 18.1, and your two-environment paper model. Include a numerical frequency change, inheritance and reproduction, one competing mechanism, and a reason the model is not a historical field observation. Cite the section rather than repeating a generic finch story.
Write in your own words or use an approved accessible equivalent. Cite a specific assigned section or figure, identify its evidence, and state one limitation or counterargument. Use the AI practice contract only for permitted coaching, never to invent observations or write the assessed response.
Transfer to a new case
Ten deep-beak immigrants enter a population, and deep beaks become more common. Does this demonstrate local natural selection?
Calibration: Not by itself. Immigration changes frequencies without showing a difference in local survival or reproduction; evidence about those processes is needed.
Evidence to retain
Adaptations & survival: environment-specific advantage explanation. Variation within a species: starting 32/32 counts. Natural selection: inherited categories, survival and offspring frequencies. Evidence & the tree of life: cited fossil/anatomical example and a branching diagram. Lab technique (natural-selection simulation): separately observe the paper-model run and inspect its round log; supplied calculations alone do not certify the practical. Retain both graphs, alternative mechanism and transfer, with integration reported separately.
Record units, calculations, source/date, uncertainty, and what is measured versus inferred. A simulation or supplied dataset must stay labeled as such. This is reading, paper-model, and data work, not authorization to collect pond water, swab people, culture organisms, dissect, expose wildlife, or ingest study materials. Use only instructor-approved prepared slides, images, or in-room materials for separately observed practical skills. Supplied data are not your observations.
Return to all eight learning pathways. Print this unit page for the student lessons; the linked five-page packet remains the separate assessment companion.
| Criterion | Developing | Proficient | Mastery |
|---|---|---|---|
| Adaptations & survival | Thinks an animal changes its own body on purpose to fit in. | Names an adaptation but can’t say how it helps survival. | Explains how an adaptation helps an organism survive and reproduce in its environment. |
| Variation within a species | Thinks all members of a species are exactly the same. | Notices differences but doesn’t connect them to survival. | Explains how natural differences within a species can make some individuals more likely to survive. |
| Natural selection | Believes traits an animal builds in its lifetime get passed on. | Describes survival but skips inheritance, reproduction or denominators. | Uses inherited variation, survival and offspring counts to explain population-frequency change under stated model conditions. |
| Evidence & the tree of life | Pictures evolution as a ladder from “lower” to “higher” animals. | Uses fossils as evidence but still ranks species as more or less advanced. | Uses fossils and shared traits as evidence and describes evolution as a branching tree. |
| Lab technique (natural-selection simulation) | Runs the simulation without tracking what survives. | Collects data but can’t explain the pattern it shows. | Runs a natural-selection simulation, records each round, and explains how the population changed. |
| Integration (cross-domain) | Makes no supported connection between the source and the science. | Uses the source but needs help connecting evidence, writing, or limitations to the science. | Independently connects History, Reading, and Writing using a cited source, appropriate evidence, a limitation, and a scientific explanation. |
Integration is reported separately and cannot lower the science grade or block a science demonstration pass. Science and practical criteria determine that pass. Use the integration guide's evidence checklist for the separately reported criterion.
“Under the hard-seed paper rule, 24 of 32 deep-beak birds survive and contribute 48 of 64 offspring: 75% of the next generation. Individuals did not change beaks. The soft-seed rule reverses the advantage; these are synthetic rules, not observations of wild birds.”
“Animals evolve to get better and better. The giraffe stretched its neck and passed it on. Humans are the most evolved, right?”
You demonstrate this unit through natural-selection simulations and fossil evidence — running the activity and explaining how a population changes over time aloud, not on a multiple-choice test. A criterion counts as mastered only when you can both show the change and explain the biology behind it. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.