Classifying living things
| English | Chinese | Pinyin |
|---|---|---|
| ancestry | 祖先 | zǔ xiān |
| classification | 分类 | fēn lèi |
| species | 物种 | wù zhǒng |
| binomial nomenclature | 双名法 | shuāng míng fǎ |
Grouping by ancestry, not by appearance
- A dolphin looks like a fish and is a mammal. A bat flies and is not a bird.
- Classification 分类 groups organisms by shared ancestry 祖先, which appearance often contradicts.
- Similar shapes evolve repeatedly because similar problems have similar solutions, which is why looks mislead.
A dolphin resembles a fish. Why is it classified with mammals?
Similar shapes evolve repeatedly because water imposes the same constraints on every swimmer.
The hierarchy
- Kingdom, phylum, class, order, family, genus, species 物种 — each level a smaller group inside the last.
- A species is usually defined as organisms that can breed and produce fertile offspring.
- ⚠ That definition breaks down for anything that does not breed sexually, which is most life by count.
Put the classification levels in order from largest to smallest.
Each level is a smaller group nested inside the one before it.
In one sentence, say why the "can breed together" definition of a species is incomplete.
Example: "Bacteria do not breed sexually, so the test cannot be applied to most life on Earth."
Binomial nomenclature
- Binomial nomenclature 双名法 gives each species a two-part Latin name: Homo sapiens, Panthera leo.
- Genus capitalised, species not, both in italic. The convention is examinable, and it is free marks.
- One name, one species, worldwide — which is the entire reason the system exists, since common names differ by language and by village.
Which is written correctly?
Genus capitalised, species not, both italic. Free marks, and losing them is marked as a content error.
Why the Latin name matters.
"Robin" is a small orange-breasted bird in Britain and a large thrush in North America. They are not closely related.
Erithacus rubecula and Turdus migratorius are unambiguous in every language and every country.
The system is not decoration or tradition. It exists because a shared name that means two things makes communication about biology impossible.
The bird called "robin" in Britain and in North America is the same species.
They are not even closely related, which is precisely why the Latin name exists.
Convergent shapes are evidence about environments, not about relatedness. A dolphin and a shark share a body plan because water imposes the same constraints, and that is a finding rather than a coincidence.
Do not capitalise the species part or forget the italics. Panthera Leo and Panthera leo are both wrong, and this is one of the few places in science where a formatting error is marked as a content error.