Lesson 2 of 6 / Evolution, species and phylogeny
From small changes to branching lineages
How are microevolution and macroevolution connected?
I can explain descent with modification and connect changes across evolutionary scales.
I can explain natural selection in evolution.Syllabus
Syllabus 9477, Core 4(c). Explain natural selection in evolution.
I can link descent with modification, microevolution and macroevolution.Syllabus
Syllabus 9477, Core 4(f). Link descent with modification, microevolution and macroevolution.
About 6 min
Make a guess. You are not marked.
Did humans evolve from chimpanzees?
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Both descend from a shared ancestor.
Evolution branches. Humans and chimpanzees are cousin lineages, both changed since their common ancestor.
The key idea
Descent with modification links inherited population changes to the divergence and diversification of lineages over longer times.
Explore the idea
Follow a branching history
Start with an ancestral population. Descendants inherit features, while mutation and reshuffling can create variation. The model does not place any future species at a predetermined goal.
This original history is a model, not a real species tree. A white centre symbol marks an inherited feature; colour differences represent other changes. Branches show descent, not physical travel. At the population-divergence stage, a drawn split does not yet claim completed speciation. The time spacing is unscaled.
Explanation
Biological evolution is descent with modification: descendants inherit features from ancestors while heritable changes accumulate. Microevolution concerns changes within populations, often measured as allele-frequency shifts. It does not mean change is trivial or always slow.
Macroevolution concerns patterns at and above the species level, including speciation, diversification and extinction. These patterns emerge through population processes over time together with splitting and loss of lineages. It is not a separate need-driven force that replaces mutation and selection.
Evolution is branching rather than a ladder towards a predetermined best organism. Different lineages inherit shared features from common ancestors and then diverge under different histories. Living species are not necessarily ancestors of one another simply because one seems simpler.
Selection is one mechanism of evolutionary change; chance sampling of alleles, gene flow and mutation also matter in appropriate contexts. A historical explanation should use evidence for particular relationships and processes rather than assuming every observed feature was directly selected for its present use.
Step by step
- 1
Identify the scale
Allele frequencies, species splitting or larger diversification?
- 2
Connect the processes
Population changes can contribute to lineage divergence.
- 3
Avoid ladder language
Use branching common ancestry.
Worked example
Work through the evidence
Two isolated populations diverge and eventually become reproductively isolated species. How does this connect the scales?
One way to explain it
Population-level changes accumulate during divergence, and the formation of separate species is a macroevolutionary outcome linked to those processes.
Why this answer works
- Speciation connects population genetics to lineage history.
- There is no requirement for one species to become more advanced.
Watch out for this
A student says: "Evolution aims to produce the most complex possible organism." What is wrong with this?
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It has no predetermined goal; outcomes reflect inheritance, environment and history.
Check your understanding
Which diagram best represents descent with modification?
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A branching tree with shared ancestors and diverging descendants
Branching captures both shared inheritance and divergence.
Quick recall
How are microevolution and macroevolution connected?