Chapter summary
Evolution, species and phylogeny, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Selection changes populations
Why does an individual's survival matter only if it affects inheritance?
Key idea and reminders
Heritable variants associated with greater reproductive success become more frequent across generations under the relevant conditions.
- Variation precedes selection.
- Heritable reproductive differences change frequencies.
- Individuals are selected; populations evolve.
Keep in mind: Mutations are not directed by need; selection changes the representation of variants.
02
From small changes to branching lineages
How are microevolution and macroevolution connected?
Key idea and reminders
Descent with modification links inherited population changes to the divergence and diversification of lineages over longer times.
- Descent connects organisms to ancestors.
- Microevolution: within-population inherited change.
- Macroevolution: broader lineage patterns.
Keep in mind: It has no predetermined goal; outcomes reflect inheritance, environment and history.
03
Use independent evidence of ancestry
Why is agreement between molecules, fossils and geography powerful?
Key idea and reminders
Independent patterns that agree with common ancestry strengthen an evolutionary explanation more than superficial similarity alone.
- Homology concerns shared origin.
- Fossils add historical sequence.
- Biogeography includes barriers and geological history.
Keep in mind: Convergent evolution can produce analogous functions in distantly related lineages.
04
Species and reproductive isolation
How can populations stop exchanging genes?
Key idea and reminders
Reduced gene flow allows divergence; speciation is established when reproductive isolation separates lineages, not merely when a barrier appears.
- Biological species: reproductive compatibility and isolation.
- Allopatric: geographical separation starts reduced gene flow.
- Sympatric: reproductive separation within the same region.
Keep in mind: The barrier reduces gene flow, but speciation requires sufficient reproductive divergence, not just location.
05
Read relationships from a tree
Does turning a branch change who is most closely related?
Key idea and reminders
Relatedness is determined by the most recent shared ancestor, not by tip order or visual closeness on a page.
- Nodes represent shared ancestry.
- Compare the most recent common ancestor.
- Tip order and unscaled line length do not define relatedness.
Keep in mind: Trace their shared node; printed spacing can be changed without changing ancestry.
06
Compare aligned sequences
Why must sequences be aligned before differences are counted?
Key idea and reminders
Compare homologous positions across suitable sequences; many independent regions give stronger relationship evidence than one short match.
- Align homologous positions before comparison.
- DNA and protein data have different resolution.
- Multiple regions strengthen inference and reveal uncertainty.
Keep in mind: Short matches can occur by chance or conservation; species relationships need broader evidence.