Wallace and the separation of populations
| English | Français |
|---|---|
| speciation/ˌspiːʃɪˈeɪʃn/ | spéciation |
| selection pressure/sɪˈlekʃn ˈpreʃə/ | pression de sélection |
What would explain this observation?
- A barrier can separate one population into two, but a barrier alone does not instantly create two species. The later inherited differences matter.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Alfred Russel Wallace independently proposed natural selection. Joint writings with Darwin in 1858 helped prompt Darwin’s book the next year. Wallace gathered evidence worldwide, studied warning colouration and made pioneering contributions to speciation 物种形成. Later evidence developed the current understanding; it was not the work of one scientist alone.
- speciation: Formation of new species through accumulated differences and reproductive isolation; selection pressure 选择压力: An environmental factor affecting relative survival and reproduction.
What provides the specified final evidence of two species?
A population may become geographically separated. The groups experience different conditions and selection pressures, with inherited variation in each. Different variants leave more offspring, and differences accumulate over generations. If the groups can no longer interbreed to produce fertile offspring, they are separate species under the specified definition.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A population may become geographically separated. The groups experience different conditions and selection pressures, with inherited variation in each. Different variants leave more offspring, and differences accumulate over generations. If the groups can no longer interbreed to produce fertile offspring, they are separate species under the specified definition.
- Use a fictional island model with a new barrier and different food sources. Explain each causal link rather than writing only isolation → new species. Identify what evidence would test reproductive isolation. Warning colouration can affect predator behaviour, but do not infer speciation merely from a different colour.
Which two habits make the investigation or model in this case more defensible?
Use a fictional island model with a new barrier and different food sources. Explain each causal link rather than writing only isolation → new species. Identify what evidence would test reproductive isolation. Warning colouration can affect predator behaviour, but do not infer speciation merely from a different colour.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: in a supplied island model, an advantageous variant rises from 10% to 35% in one population. Increase = 25 percentage points, not 25%. Relative percentage increase = (35−10)/10×100 = 250%. Neither statistic alone shows that fertile interbreeding has stopped.
Variant frequency rises from 12% to 42%. Find the increase in percentage points. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Variant frequency rises from 12% to 42%. Find the increase in percentage points.
The result is 30 percentage points. Known: in a supplied island model, an advantageous variant rises from 10% to 35% in one population. Increase = 25 percentage points, not 25%. Relative percentage increase = (35−10)/10×100 = 250%. Neither statistic alone shows that fertile interbreeding has stopped.
Check the conclusion and its limits
- Geographical isolation is not proof of a new species. Different appearance alone is insufficient. The key final criterion is failure to produce fertile offspring by interbreeding, and the explanation must connect inherited variation with reproductive success over generations.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A geographical barrier instantly creates a new species. This claim is false: Geographical isolation is not proof of a new species. Different appearance alone is insufficient. The key final criterion is failure to produce fertile offspring by interbreeding, and the explanation must connect inherited variation with reproductive success over generations.
Wallace and the separation of populations: A population may become geographically separated. The groups experience different conditions and selection pressures, with inherited variation in each. Different variants leave more offspring, and differences accumulate over generations. If the groups can no longer interbreed to produce fertile offspring, they are separate species under the specified definition.
A geographical barrier instantly creates a new species.
Geographical isolation is not proof of a new species. Different appearance alone is insufficient. The key final criterion is failure to produce fertile offspring by interbreeding, and the explanation must connect inherited variation with reproductive success over generations.
Formation of new species through accumulated differences and reproductive isolation: write the technical term.
speciation means Formation of new species through accumulated differences and reproductive isolation.