Relatedness = recency of common ancestry
– grandparents vs. great-grandparents
– ≈ 6 Million years ago (Ma) vs. ≈ 600 Ma
• 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….
Is a frog more closely related to a Is a frog more closely related to a trout or a human?trout or a 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
TroutTrout FrogFrog LizardLizard MouseMouse HumanHuman
Why might you go wrong?If you look “along” the top
You can change the order without changing the tree
Fish FrogLizardMouseHumanFishFish FrogFrog LizardLizard MouseMouse HumanHuman
Trout FrogLizardMouseHuman
-> The same tree depicts the same relationships
On this tree, is a frog more closely related to a trout or a human?
Is a gibbon more closely related to a human or a macaque?
Don’t be distracted by similarity
Remember not to look “along the top”
Non-monophyletic group
Some members are more closely related to organisms outside
the group
Monophyletic group(clade)
Members are more closely related to
each other than to any organisms
outside the group
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