1. Relatedness = recency of common ancestry
You are more closely related to your first cousins than your second cousins because….
You are more closely related to a chimpanzee than to a worm because….
grandparents vs. great-grandparents
≈ 6 Million years ago (Ma) vs. ≈ 600 Ma

2. Is a frog more closely related to a trout or a human?

3. Why might you go wrong? If you look “along” the top
Trout
Frog
Lizard
Mouse
Human
But this is not how evolution happened
All these species are alive today: A living trout is not an ancestor of a frog
The order “along the top” can change without changing the content of the tree

4. You can change the order without changing the tree
Fish
Frog
Lizard
Mouse
Human
Fish
Frog
Lizard
Mouse
Human

5. On this tree, is a frog more closely related to a trout or a human?
Mouse
Lizard
Frog
Note one can add all sorts of info onto trees. Character changes, biogeography, chemical features, time, etc.
-> The same tree depicts the same relationships

6. Is a gibbon more closely related to a human or a macaque?
Note one can add all sorts of info onto trees. Character changes, biogeography, chemical features, time, etc.
Don’t be distracted by similarity

7. Remember not to look “along the top”
Note one can add all sorts of info onto trees. Character changes, biogeography, chemical features, time, etc.

8. Non-monophyletic group
(clade)
Members are more closely related to each other than to any organisms outside the group
Non-monophyletic group
Some members are more closely related to organisms outside the group

9. Biological classifications should reflect evolutionary relationships
They should mirror phylogenetic trees
Only clades should be named
Most named groups you know of are clades
But there are a few exceptions:
Fish, invertebrata, reptiles, protista, prokaryota