Common Ancestry
Introduced| English |
|---|
| common ancestor/ˈkɒmən ˈænsestə/ |
| lineage/ˈlɪnɪɪdʒ/ |
All life is related
- Every living thing, from a bacterium to a blue whale, is connected.
- Trace any two species back far enough and their family lines meet.
- That meeting point is a shared ancestor.
- This idea — common ancestry — ties all of life into one tree.
The common ancestor
- A common ancestor 共同祖先 is an earlier species two others both descend from.
- Humans and chimps did not come from each other — they share an ancestor.
- The more recent that shared ancestor, the more closely related the species.
- Follow every lineage 谱系 back far enough, and they all connect.
A common ancestor of two species is…
A common ancestor is an earlier species from which both modern species descend.
Universal features
- Almost all living things share deep, basic features.
- They all use the same DNA genetic code.
- They all build proteins with ribosomes and run on ATP.
- These universal traits point to a single origin of life.
Tracing back to a common ancestor
Step back through time - the further back you go, the more distantly related species share an ancestor.
Which feature is shared by nearly all living things, pointing to a common origin?
Almost all life uses the same genetic code, ribosomes, and ATP — strong signs of shared ancestry.
Species that share a more recent common ancestor are more closely related.
The more recently two species shared an ancestor, the closer their relationship.
The tree of life
- Because all life is related, we can draw it as one branching tree.
- Nearby branches are closely related; distant branches split long ago.
- The deeper a shared feature, the older the ancestor that had it.
- Every species is a twig on this single, ancient tree.
The line of descent connecting an ancestor to its descendants is a ____.
A lineage is the continuous line of ancestors and descendants through time.
Select all true statements about common ancestry.
Humans did not evolve from chimps — the two share an ancestor. The other three are correct.
Common ancestry does not mean one living species came from another. Humans did not evolve from chimpanzees. Instead, humans and chimps both descend from a shared ancestor that lived millions of years ago and was neither.
The universal genetic code:
- In a human, an oak tree, and a bacterium, the codon $\text{A–U–G}$ codes for the same amino acid.
- There is no chemical reason it had to be this way.
- The best explanation is that all three inherited the code from one common ancestor.
All life shares common ancestry: any two species trace back to a common ancestor, and a more recent shared ancestor means a closer relationship. Universal features — the same genetic code, ribosomes, and ATP — show that every lineage connects to one ancient origin. Related species share ancestors; they do not descend from one another.