| DATE: | Thursday, April 26, 2001 |
| TIME: | 4:30-5:30 PM |
| PLACE: | LN 2205 |
| SPEAKER: | L. Billera, Cornell University |
| TITLE: | Geometry of the Space of Phylogenetic Trees |
We consider a continuous space which models the set of all phylogenetic trees having a fixed set of leaves. This space has a natural metric of nonpositive curvature (i.e., it is CAT(0) in the sense of Gromov), giving a way of measuring distance between phylogenetic trees and providing some procedures for averaging or otherwise doing statistical analyses on sets of trees on a common set of species. This geometric model of tree space provides a setting in which questions that have been posed by biologists and statisticians over the last decade can be approached in a systematic fashion. For example, it provides a justification for disregarding portions of a collection of trees that agree, thus simplifying the space in which comparisons are to be made. This is joint work with Susan Holmes and Karen Vogtmann.