And we ply optimality criteria, so I was applying what
is called minimizing the branch length, so the minimizing of the number of changes.
And so I was using the minimim number of steps, or changes, on those
trees, under what we call the critrium
of maximum parsiomoney, or simple character parsimony.
But there are other ways in which
scientists now look at trees. Mostly with respect to DNA distances.
So there's all kinds of tree-based, model-based approaches that
can be used to to generate phylogenetic trees from, say, DNA sequences.
So here's a tetrapod tree and it just, to make
it very simple, all tetrapods from frogs to lizards,
birds, and then mammals all have four legs, hence
called tetrapods. Before then, they didn't have four legs,
but these have four legs, and therefore as synapomorphies, they're grouped together.
All of these organisms from here on up,
are called amniotes because of the way of the membranes that are in, in
surrounding the eggs and some of the them have,
mammals of course, have mammary glands, they have hair, they also have single
bones in the lower jaw compared other of these tetrapods.
So there are different characters we can place on here and
there are special biochemical characters that unite
birds and the squaw-mate reptiles, lizards and snakes.
And then within mammals, there are
carnassial teeth, which bring the carnivores
together, that, you know, the cheetah and the jaguar, for instance, together.
Now you can see from this thee, you can see that
it's highly predictive, so if a colleague of yours goes
out and says, oh, I just discovered a new mammal.
Well, from what you know about the phylogenetic
relationships of mammals, you can make a predication.
Well, they're going to have mammary glands.
They're going to have have hair and so forth.
And this is really important for
the discovery of new life forms, because if we start
classifying those, then we can start predicting what are their properties.
And that's exceedingly important and we'll get into that in future lectures.