Outgroup analysis provides clues to which traits derived, which ancestral
o evolution does not always proceed toward greater complexity (4 legs ->
Reading and Building phylogenies
o "related to" =/= "descended from"
related to cousins, related to siblings, modern species are all
related to one another does not descended from one another
o more complex =/= "more evolved"
o relatedness =/= similarity
not all similarities are homologies
not all homologies are synapomorphies
Is this trait ancestral or derived? or neither (cannot tell)
o present in outgroup and ALL of ingroup
it is ancestral
don't know for sure, but it is very likely that it is ancestral
o Present in outgroup and SOME of ingroup?
it is ancestral
more likely its ancestral, but it might be lost in some lineages
o Absent in outgroup, present in SOME of ingroup
it is derived
a trait is not found in the outgroup, only some of ingroup have it
then its derived, not ancestral
o Present in outgroup, but NONE of ingroup?
We cannot tell, it can go either way
o Absent in outgroup, present in ALL of ingroup?
we cannot tell This reasoning relies on parsimony
o the simplest explanation is usually the best
o whichever tree requires the smallest number of evolutionary changes
(gains or losses of a trait), is probably correct
o Parsimony often used to evaluate potential trees
How many potential phylogenetic trees are there?
o with increasing number of taxa (t), number of candidate trees increases
o 2 taxa 1 possibilities
o 3 taxa 2 possibilities
o 4 taxa 15 possibilities
o 10 taxa 34.5 million possibilities
Using parsimony to evaluate candidate trees
Which tree is more likely to be correct?
First identify which traits are synapomorphies