Speciation
| English | Chinese | Pinyin |
|---|---|---|
| species | 物种 | wù zhǒng |
| reproductive isolation | 生殖隔离 | shēng zhí gé lí |
| allopatric | 异域 | yì yù |
How new species are born
- Natural selection changes a species over time — but where do new species come from?
- Sometimes one species splits into two.
- This splitting is called speciation.
- It is how the whole tree of life keeps branching.
What a species is
- A species 物种 is a group that can interbreed and produce fertile offspring.
- All members share one gene pool.
- Two organisms that cannot interbreed belong to different species.
- So the key to a new species is breaking that ability to interbreed.
Two organisms belong to the same species if they can…
A species is a group that can interbreed and produce fertile offspring together.
Reproductive isolation
- For one species to become two, the groups must stop interbreeding.
- This is called reproductive isolation 生殖隔离.
- Once isolated, the two gene pools no longer mix.
- Each is then free to change in its own direction.
How a new species forms
Step through speciation - one population is split, the halves diverge, and eventually they can no longer interbreed.
What must happen for one species to split into two?
Speciation needs reproductive isolation — the groups can no longer interbreed, so their gene pools split for good.
Once separated, the two groups can accumulate different mutations and changes.
Separated gene pools diverge through different mutations, selection, and chance until they cannot interbreed.
Allopatric speciation
- A common route is allopatric 异域 speciation: a geographic barrier splits a population.
- A river, mountain range, or ocean divides the group in two.
- Over generations, different mutations and selection make the halves diverge.
- Eventually they differ so much they can no longer interbreed — two species.
Speciation caused by a geographic barrier splitting a population is called ____ speciation.
Allopatric speciation happens when a physical barrier — like a river — separates a population.
Select all true statements about speciation.
Looking different is not enough — the test is whether they can interbreed. The other three are correct.
Looking different is not enough to make a new species. Two groups become separate species only when they are reproductively isolated — unable to interbreed and produce fertile offspring. Colour or size differences alone do not count.
A river makes two squirrels:
- Long ago, the Grand Canyon split one squirrel population in two.
- The two sides could no longer meet or interbreed.
- Over thousands of years each side changed separately — today they are two distinct species.
Speciation is one species splitting into two. It requires reproductive isolation — the groups can no longer interbreed, so their gene pools diverge. In allopatric speciation, a geographic barrier splits a population; the separated halves change until they become distinct species.