7.7 Common Ancestry

All life is related

The evidence points to all living things sharing a common ancestor. Nearly every organism uses the same genetic code, the same basic molecules (DNA, RNA, ATP), ribosomes, and membrane-bound cells. These deep similarities are hard to explain unless life shares a common origin.

Conserved features

Core processes and genes are conserved — kept nearly the same across huge spans of evolution — because they are essential. The more features two species share, the more recently they likely share a common ancestor.

Key terms

Common ancestry

The idea that all living things descend from a shared ancestor.

Universal genetic code

Nearly all organisms use the same codon-to-amino-acid code — evidence of shared ancestry.

Conserved core processes

Essential processes and genes kept nearly the same across evolution.

Shared molecules

DNA, RNA, ATP, and ribosomes are found across nearly all life.

Evidence of relatedness

More shared features usually means a more recent common ancestor.

Try an AP-style question

All eukaryotes have membrane-bound organelles, linear chromosomes, and genes with introns. What does this best support?

1. Prokaryotes descended from eukaryotes
2. All eukaryotes share a common ancestor
3. Eukaryotes evolved separately many times
4. Eukaryotes and prokaryotes have no shared features