An Introduction to Phylogenetic Analysis - Association for Biology ...

72 ABLE 2005 Proceedings Vol. 27 Kosinski
Table 8. Reordered character matrix for Example C1.
3 4 5 6 8 11 12 15 16 17 18 20
A X
D X X
C X X X X X
E X X X X X X X X
F X X X X X X
In the (A, D) group, which species came first? It seems clear that the A ancestor evolved first and
then the D ancestor came from the A ancestor by adding character 12. Likewise, for the (C, E, F) group,
E is C with the addition of derived characters 15, 16, and 18, and F is C with the addition of derived
character 17. Therefore, it is parsimonious to conclude that the E and F ancestor evolved from the C
ancestor.
Finally, in addition to its other derived characters, B has 3 and 4, which no other species has. We
express this by putting the ticmarks for derived characters 3 and 4 on the “B” branch. Derived characters
on the main diagonal are passed along to species that branch off the diagonal after that point, but derived
characters on the branches are only passed to the species that come from that branch.
The completed C1 cladogram is:
15, 16, 18
OG
Figure 13. The complete cladogram for Example C1.
D
12
B
4
3
C E
Can you follow the cladogram and see that species B has derived characters 8, 6, 11, 3, and 4, and
that E has derived characters 8, 6, 11, 5, 20, 15, 16, and 18?
The cladogram above not only can explain all the data with a minimum number of steps, but it has
accurately determined the way the computer simulation generated species A-F. This gives us confidence
that cladistic methods can be used to infer evolutionary history.
8
6
11
5
20
17