More differences mean an older split
- The idea
- Predict
- See it
- Why
- Check
The idea
“Species with more sequence differences are more closely related, or split more recently.”
A bigger number can look like a stronger link. A difference count works the other way, because differences build up with time.
The short version
The mistake: Species with more sequence differences are more closely related, or split more recently.
What's actually true: Differences pile up the longer two lineages have been apart, so more differences mean an older split and a more distant relative.
- Once two lineages split, each one collects its own mutations. Over time, more and more sites differ between them.
- If a gene changes at a fairly steady rate, the count works as a molecular clock. A fossil date sets the rate.
- So the pair with the fewest differences shares the most recent common ancestor. They are the closest relatives.
On the exam: Read differences as time apart. The fewest differences mark the most recent split and the closest relatives.