Classifying living things
Introduced| English | Meaning |
|---|---|
| species/ˈspiːsiːz/ | A group of organisms whose members can usually interbreed to produce fertile offspring. |
| classification/ˌklæsɪfɪˈkeɪʃn/ | Arranging items or organisms into groups according to shared features or a defined system. |
| ancestry/ˈænsestri/ | ancestry |
| binomial nomenclature/baɪˈnəʊmɪəl nəˈmeŋklətʃə/ | binomial nomenclature |
A shared name can hide different groups
- In the supplied cat-family table, lion is Panthera leo, tiger is Panthera tigris, and domestic cat is Felis catus. There are three species, two genera and one shared family, Felidae.
- Classification 分类 uses evidence about relationships and shared ancestry 祖先. One similarity of appearance can contribute evidence, but cannot establish complete relatedness by itself.
Why should classification not be based only on one similarity of appearance?
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Appearance can contribute evidence, but one feature does not establish complete relatedness. Identification keys and evolutionary trees serve different tasks.
Follow the nested levels
- A traditional sequence runs kingdom, phylum, class, order, family, genus and species 物种. A family may contain several genera, and a genus may contain several species.
- Lion and tiger share Panthera but are not the same species. Felis differs from Panthera without requiring a different family; keep the level named in the question.
Order these traditional classification levels from broad to specific.
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Genus can contain several species, while a family can contain several genera. Keep the named levels distinct.
Organisms in different genera must belong to different families.
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The supplied Felidae example includes Panthera and Felis. Different genera can occur within a shared family.
How many genera occur in the supplied lion, tiger and domestic-cat table?
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Panthera and Felis are two genera; there are three species.
Write a complete scientific name
- Binomial nomenclature 双名法 uses the genus and specific epithet. Capitalise the genus, use lower case for the epithet, and italicise both in print: Panthera leo.
- The epithet “leo” alone is not the complete species name. Common names vary, so report the full scientific name and the classification source used.
Which is written correctly?
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Capitalise the genus, use a lower-case specific epithet and italicise both in print. Name formatting supports communication; it is not a guarantee of marks or proof of ancestry.
Use an identification key for its intended task
- A simple key separates specimens by stated features. For a supplied three-card task, a red card leads to A; a green card with a smooth edge leads to B; a green card with a toothed edge leads to C.
- This identifies a card from its features. The key's first branch does not prove that B and C share a more recent ancestor than A, or show the order of evolution.
An identification key and an evolutionary tree answer different questions. Do not turn the order of tests in a key into an ancestry claim.
The first branch of the supplied identification key proves the order of evolution.
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False: it separates stated features for identification and does not establish an evolutionary history.
The supplied key receives a green card with a toothed edge. Which label does it identify?
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Red leads to A; green/smooth to B; green/toothed to C.
Choose a species criterion that can be applied
- A breeding criterion can be useful for some sexually reproducing organisms, but cannot be applied in the same way to asexual organisms or fossils known only from preserved remains.
- Definitions and evidence depend on the organisms and question. A name or one visible trait does not remove the need to examine the relevant evidence.
In one sentence, say why the "can breed together" definition of a species is incomplete.
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Example: “A breeding criterion cannot be applied in the same way to asexual organisms or fossils.” Definitions and evidence depend on the organisms and question.
Report both identity and scope
- In this table, the three species share a family, while only lion and tiger share a genus. Use these exact statements rather than saying all three are the same animal.
- The names and family are supplied from ITIS cat record and lion/tiger records, checked 2 October 2026. This small table is a teaching comparison, not a complete evolutionary analysis.
Keep family → genus → species distinct, write both name parts, and explain whether you are identifying a specimen or investigating relationships.