Species can split without a wall between them
- The idea
- Predict
- See it
- Why
- Check
The idea
“A new species can only form after a river, mountain or ocean splits a population in two.”
The classic picture is a canyon splitting a population in two. A barrier is only one way to keep groups from mating.
The short version
The mistake: A new species can only form after a river, mountain or ocean splits a population in two.
What's actually true: Speciation needs gene flow to drop, which can happen in one shared place through polyploidy, host choice, timing or mate choice.
- Speciation happens when gene flow between two groups drops and their gene pools diverge.
- In allopatric speciation, a physical barrier like a river blocks gene flow. In sympatric speciation, groups diverge in the same area.
- Sympatric routes include polyploidy in plants, a new host or habitat, different breeding times, and mate choice.
On the exam: Ask what blocks gene flow. A barrier can, and so can polyploidy, timing or mate choice in one place.