Selection needs something that copies itself first
- The idea
- Predict
- See it
- Why
- Check
The idea
“Life had to start with a membrane, a way to capture energy, or DNA.”
Every cell has a membrane, DNA and an energy supply, so it's natural to start there. Selection can't improve any of them until something makes copies.
The short version
The mistake: Life had to start with a membrane, a way to capture energy, or DNA.
What's actually true: Natural selection can't act until something copies itself with variation, so replication comes first.
- Natural selection needs heredity, variation and differences in reproduction. Copying gives heredity, and copying errors give variation.
- When copies differ in how fast they copy, the faster ones become more common. That is selection, and it can work on molecules alone.
- Membranes and energy capture help, but selection can favor them only in something that already copies itself. The same goes for a later switch to DNA.
- That is why the RNA world hypothesis starts with RNA. It can store information and also catalyze reactions.
On the exam: Selection can improve something only after it copies itself, errors and all.