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 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 TroutFrogLizardMouse Human Why might you go wrong? If you look “along” the top

You can change the order without changing the tree Fish FrogLizardMouseHumanFishFrogLizardMouseHuman

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