**Speaker**: Ruth Charney (Brandeis)

**Title**: Phylogenetics and the Geometry of Tree Space

**Abstract**:
I will discuss some recent work of Billera, Holmes, and Vogtmann in
which they apply techniques of geometric group theory to problems in
phylogenetics. One of the key problems in phylogenetics is to
reconstruct evolutionary trees from DNA data. The space of all possible
trees (with fixed number of leaves) has a natural metric. This metric
turns out to be CAT(0), that is, it has certain properties analogous to
the path metric on a manifold of non-positive curvature. I will
discuss these properties and how they can be used to help solve some
problems in phylogenetics.