Not every changed structure is vestigial
- The idea
- Predict
- See it
- Why
- Check
The idea
“If a structure got shorter, disappeared or does something new, it's vestigial.”
Shrunken, missing and reshaped parts all look like marks of evolution. Vestigial names only the leftover that stays but no longer works.
The short version
The mistake: If a structure got shorter, disappeared or does something new, it's vestigial.
What's actually true: A vestigial structure is a reduced leftover of a part that worked in an ancestor. It's still there but does little or nothing now.
- A part with a new job, like a whale flipper, still works, so it isn't vestigial. Its bones match your arm's, which makes them homologous.
- A part that is gone can't be vestigial. A part that is short but still used isn't vestigial either.
- A vestigial remnant is evidence of evolution. It points to ancestors that used the part.
On the exam: Vestigial means still there but doing little or nothing. A part with a new job doesn't count.