Phylogeny and Reconstructing Phylogenetic Trees
Introduction
So, what is phylogeny? It's the study of the evolution of life forms.
One phylogenetic tree, also called a cladogram or a
dendrogram, is displayed below. It
is a tree of several
life forms and their relations. In this display, time is the vertical
dimension with the current time at the bottom and earlier times above it.
There are five extant species (species currently living) named from 1 through
5. The lines above the extant species represent the same species, just in
the past. When two lines converge to a point, that should be interpreted
as the point when the two species diverges from a common ancestral species,
the point being the common ancestral species. And so it goes until eventually,
some time in the past, all the species derived from just one species, the
one displayed as the top point.
The phylogenetic tree displayed above was randomly generated. If you like,
you can click on the button labelled "New Tree" to generate a different
phylogenetic tree. You can also change the number of extant species by editing
the field labelled "Species".
A couple of comments about the horizontal dimension of the phylogenetic
tree. It doesn't mean anything! Any tree can be displayed in two dimensions,
and so these phylogentic trees are. It is completely arbitrary whether a
branch of the tree is placed to the left or to the right of a dot. So, a tree
with two species, 1 and 2, with a common ancestor "dot", could be drawn with
either species 1 or species 2 on the left, and the other species on the right.
to the cover page.
to the next page about mutations.
David E. Joyce
Department of Mathematics and Computer Science
Clark University
Worcester, MA 01610
Email: djoyce@clarku.edu
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