Big differences can hide a shared ancestor
- The idea
- Predict
- See it
- Why
- Check
The idea
“If two groups are this different, they must have started out separately.”
A mushroom and a person seem too different to be related. Look inside, and their cells run on the same basic machinery.
The short version
The mistake: If two groups are this different, they must have started out separately.
What's actually true: Groups that look very different can still share deep features, like the genetic code, that point to one common ancestor.
- A feature shared because it was inherited from a common ancestor is a homology. Your arm bones and the genetic code are examples.
- Differences pile up after lineages split, as each adapts to its own way of life. In time, relatives can look nothing alike.
- Some parts do arise separately, like bird and insect wings. Those wings are not homologous, but the groups still share an ancestor.
On the exam: Weigh deep shared features, not surface differences. Those point to a common ancestor.