Ancestral trait and Derived trait

[Ahmed Abdullah]

In phylogenetic tree construction , it is important to correctly identify ancestral and derived traits. But how one actually determine which trait is ancestral and which one is derived? I know shared trait among certain group indicate its ancestral of that group. That is a very powerful principle , I know .. .. . but is it the only principle? I feel there is more.. Please enlighten me.

 

[mel_c]

Hi Ahmed,

You pretty much summed it up. Ancestral means the trait was inherited from the ancestor, so all branches which descend from the ancestor will have this trait (it will be 'shared' among them because they all got it from their common ancestor). Any unique traits they possesses must have been derived after the split, therefor it is called derived.

Hope that helps!