Hi. It's Mr. Andersen and welcome to biology essentials video number six. This
is on phylogenetics. And phylogenetics is essentially the evolutionary history or the
evolutionary family tree of organisms. If you look on this page we've got a number of
pictures, we've got a number of pictures of cetaceans, so a bunch of whales. So the goal
of phylogenetics is to create a phylogenetic tree. In other words a tree that shows who
is related to who. In other words, is the humpback whale most related to the gray whale
or to the minke whale or to the fin whale. And so phylogenetics is actually a really
fascinating area right now because with all of the DNA evidence that we have we're able
to put together a wonderful picture. And our goal is that the phylogeny will match taxonomy.
In other words we can give names to organisms based on who they're related to. But the more
you learn about this the more you realize that all life is very very similar. We have
similarities between all of it. So let's get going on phylogenetics. And so basically speciation
is when one organism or one population or one group eventually diverges and so they
can't interbreed any more. It's the simplest way to think about speciation. And so phylogenetics
and phylogenetic trees require speciation to have occurred. There are a number of different
phylogenetics trees. The one that we'll talk a lot about are called cladograms and they
use what are called clades. And so it's just a specific type. But a phylogenetic tree shows
the evolutionary history of an organism. Now how do we figure that out? Well we could use
all the tools at our disposal. I am going to talk about two specifically today. One
is morphological. Morphological is the structure that you have. And the other is molecular.
And so morphologically I am going to talk about hearts and how hearts have changed over
time as they've required more and more things. And then the last is molecular. In other words
how do we use DNA to figure out who is related to whom. So those are phylogenetic trees.
This is the evidence that we use to figure it out. And then at the end I am going to
talk more about cladograms and how you create a cladogram. And so let's start with the biggest
phylogenetic tree of all, phylogenetic tree of life. So if this is life down here, so
if life began you know 3.6 billion years ago, it's diverged into all these different lineages.
And so this right here would be a phylogenetic tree. A phylogenetic tree of life. Now the
one thing I want to point out and Darwin was the first person to do this, is that whenever
you have a tree that suggests that there's common descent. And what does that mean? Well
bacteria, archaea and eukarya, since they're all on the same phylogenetic tree, it means
that they all came from that common ancestor. And so every time we have a branch point on
here, so what does this suggest, that branch point right there suggests where that tree
diverged into the eukarya and then the archaea that we have. And so the idea of descent is
a long one, but the more evidence that we gather the more we realize that Darwin was
right on. Now we have to figure out who is related to who. And so let's start at evidence
that we have. So the evidence that we can use to make a phylogenetic tree, let's start
with the first one and is morphological. Morphological are the structures that you
have. And so this is a phylogenetic tree of vertebrates. And so we've got early vertebrates,
we've got time periods over on the side, but we're most interested in the mammals. We've
got birds, reptiles, amphibians, fishes. And so how did scientists figure out who's related
to who? Well, we can choose one characteristic and then we can trace that through time. We
can look at one thing and see how it's changed over time. So a perfect example would be the
heart. The heart began in fishes as a two chambered heart. A two chambered heart really
just has one valve. In other words, the blood is going to flow in this direction and then
there's a valve that opens in this direction, so once the blood moves through it, it can't
come back in. And so it's just a muscle that has a valve on the inside of it. And so what's
the function of the heart? Well in a closed circulatory system, in other words, insects
don't use a closed circulatory system, they use, their blood just goes everywhere in through
the tissues. But in a closed circulatory system, in a fish, the blood, which in blue in this
case just means that it is deoxygenated, is going to go through the gills, and then it's
going to be oxygenated, so it's red, and then its going to go through the body and the tissues
in the body, and then it's going to drop off that oxygen and then it comes back to the heart
again. And so a two chambered heart, a better way to think about what a two chambered heart
is, is it's simply a single loop. So we just have this one loop through the gills and back
to the body. And for fishes that works great. The problem is that as we move on to land
there are quite a few more constraints as you move, especially as you move towards being
like a warm blooded organism. And so the constraints get heavier and heavier and so it's okay to
have a two chambered heart, works great if you're a fish, but as we move on to land then
it has to modify itself. And so again we just have this one loop. The major problem is that
once it goes through the gills you loose a lot of the pressure. And so you loose the
pressure and so it's hard to move that through the rest of your body. Works great if you're
floating in water, but as you move on to land, we don't have that pressure. Okay, so let's
go to a three chambered heart. Now three chambered heart arrives in the amphibians. And so things
like a frog have a three chambered heart. So they've got three delineations. We've still
got that loop that goes through the lungs and mostly in amphibians it actually goes
through the skin where they pick up oxygen. But you see that we now have a problem here.
We're not losing that pressure, in other words we're able to pump the blood to the skin and
the, excuse me, we are able to pump it to the skin and the lungs and then we have a
separate loop that goes through the body, so we still don't have to deal with that pressure.
But the problem comes in right here, and that is that we have a mixing of the oxygenated
and deoxygenated blood. And so it's purple. Now is that a problem? Well it's a problem
if you are anything above, or spend more time on land then amphibians do. And so it works
great for amphibians, but you have a mixing of oxygenated and deoxygenated blood. And
so if you look at this loop, it's a double loop, but if you look at it and say okay,
now let's move up to the reptiles and now we have to move more blood and we don't want
as much of this mixing here because we're going to lose a lot of the oxygen. Well think
about it as an engineer, how could you solve this? Well a three chambered heart works like
this and what it does is it has a septa that's built right down here in the middle of the
heart and that septa separates the deoxygenated from the oxygenated. It still has a little
bit of mixing of the blood but that works great because they're cold blooded critters
and so as they move that body, that blood around their body they can actually keep themselves
a little bit warmer. But that's a three chambered heart and as we move on to endothermy, as
we move on to birds and mammals, that just doesn't cut it. And so we think that birds
and mammals both evolved this independently and you can see on here that birds branched
off from reptiles and mammals branched off earlier from a common ancestor. And so we
eventually have the arrival of the four chambered heart. What's the four chambered heart do?
Well you can see that that septa that went right down the middle has completely closed
off. So we don't have any mixing of the oxygenated and deoxygenated blood. And so birds and mammals
have this morphological change and they did it because they're endothermic. In other words
they require a constant body temperature. And so we can trace this morphological evidence
through the organisms and we can say who's related to who. In other words is we have
a three chambered heart that's shared by everything above here, that means that on our phylogenetic
tree we want to at least put those on the same branch. Next I want to talk about molecular
data. So molecular data is looking at the DNA. So looking at the genetic code. And so
this is a study that was done in 2009. And what they were trying to figure out is where
metazoans fit and who is related to whom. And every time I have a new biology book I
find that this is actually organized a little bit differently. But we have this group down
here of the, so the jellyfish and the sponges down here on the bottom. And then we have
this group up here which contains things like us. And so scientists weren't sure if this
branched off early or if these branched separately. And so what they did is they gathered a huge
amount of DNA evidence. And so you can see here that this was a very large study done
on a number of different families a number of different groups of animals. And they looked
at mitochondrial DNA, proteins, ribosomal RNA. They looked at a number of different
things and they figured out, this is very recent, that this branch and this branch are
actually sister branches. The branch up here that makes us and the branch that makes the
jellyfish have kind of separated a long time ago and they have been evolving since then.
And so this is a great way, this would be a phylogenetic tree that we can use molecular
evidence to answer a problem. But you have to gather a huge amount of data before you
can actually do that. And on here you can see that they actually have an out group which
is group of fungi which is not an animal, but it's a way that we can actually make comparisons
to that molecularly and then we can figure out the connections. Okay. Last thing I said
I would talk about are cladograms. Cladogram uses what is called a clade. And a clade,
if I remember right comes from I think Latin. It means a branch. And so a clade is simply
a group that has an organism and all, and I would circle the word all, of it's descendants.
And so this right here is a clade, because it has this organism and all the descendants
that come from that. Where this, the orange, is going to be a clade because it has this
organism and it has all of the descendants that come from that. But green, right here,
we would not call this a clade and the reason why is that you would have this organism right
here and all of these descendants but you're missing a number of them over here. And so
that's not a true clade. And so cladograms are going to, it's the definitive answer of
who's related to whom. But you use two things. You use molecular and DNA for sure, evidence,
but the other thing that you're going to use are something called synapomorphies. And a
synapomorphy is going to be a characteristic that's shared by all of those in the clade.
So a couple of good ones as we look through the fossil evidence of dinosaurs, we branch
all the dinosaurs into two groups. The ornithischia and saurischia. And these are all, saurischia
if I remember right means bird hipped and ornithischia means lizard hipped. And so it's
a way to branch these groups and so a synapomorphy would be this characteristic. In other words,
saurischia is going to be in this hip structure, is going to be shared by everything in this
clade. And so the goal is to have a clade that has similar characteristics and it also
doesn't leave anything out. A real example that you're probably familiar with would be
reptiles. Reptiles is a silly term because reptiles used to be this blue area right here.
It contained things like turtles, crocodiles and birds we left out of that. And so if you
look at this, this group is what's called paraphyletic and so reptiles as a group was
paraphyletic. It had all of these descendants but it lacked the birds. And we now know that
birds are apart of this group. And so the goal of a cladogram is to create what are
called monophyletic groups. Monophyletic would be this, yikes, would be this yellow group
right here because it contains this and all of the descendants of that, that move from
here. So polyphyletic means you have groups that come from different areas. So if we were
to put mammals and birds together in one group that would be polyphyletic. And paraphyletic
is when you have some organisms but not others. And so what's the goal? The goal of a cladogram
is to figure out all of life. So we put all of life on branches and we figure out who's
related to whom. And then, hopefully we can use a naming system and classify all of life.
It seemed like a daunting task at one time but molecular evidence is giving us an in
roads to that and it's a really hot topic as far a biology goes today. So that's phylogenetics
and I hope that's helpful.