Hi. My name is Melina Hale.
I'm a professor at the University of Chicago.
In my lab, we study neurobiology,
biomechanics,
and evolution.
I'm going to present two different topics.
The first is an introduction to evolution.
Then we'll go on to talk about
a specific example from my lab
of how we map the nervous system
and aspects of the nervous system
onto the evolution of animals.
We work in my lab, specifically,
on vertebrate animals,
things like fish and tetrapods,
mammals, and reptiles,
and so I'm going to focus on that
part of biodiversity
in my talks.
There's a lot of other organisms out there, of course,
invertebrates, and insects, and plants,
and microbes,
that we won't touch on in these lectures.
So, we'll start with this introduction into evolution.
What is evolution?
Now, Charles Darwin
originally proposed the theory of evolution,
which can be summarized
in a very succinct phrase:
descent with modification.
Now, let's break that down a little bit, though,
to a broader definition,
which is change in the heritable characteristics
of organisms
from generation to generation.
We can break that down
even further to look at
the component parts of that sentence.
First, if we think about
this idea of generation to generation,
that means that when we look at evolution,
we're really not talking about changes
in individuals
or over short time frames.
Instead, we're talking about
changes that we see
over a long history
of the descent of an organism over time.
What about heritable characteristics?
Well, we all have lots of characteristics
to our bodies.
We may have big muscles
if we exercise a lot,
we may have had injuries in our lifetime
that have given us scars.
Those are not heritable characteristics.
Heritable characteristics
are the types of traits
that we pass on to subsequent generations,
or that we inherited from our parents
and grandparents.
Heritable characteristics
are an important part of evolution,
because it allows transmission
from one generation to the next,
and on and on through evolutionary history.
Now, the last part of this is change,
and change is also really important.
There has to be the ability in evolution
for these heritable characteristics
to vary,
to change in response to environmental factors
that might favor one type of characteristic
or another,
and we'll come back to that.
And that's what Darwin was getting at
with this idea of modification,
that there's going to be change
in how organisms are organized
and how they look over time.
So, here's an example,
a cute picture of a pair of dogs
and their puppies,
where you can really see
the variation in characteristics,
even in one generation.
If you look at the parents
and you look at the pups,
you can see some of the puppies
look like one parent,
with, you know, pure light fur,
others look like the other parent,
with very dark fur around the face,
but yet there are other puppies in the litter
that look different yet again,
that have a mix of the characteristics
of those two adults.
So, you can get a sense
of the variation in this image
that can be explored in evolution
and capitalized upon
through evolutionary time.
One example of variation
that's been really important for us
to understand how we can
change the characteristics,
the features of a species,
over time,
is the peppered moth.
So, these two moths,
that look very, very different
-- the light one on the left
and the dark one on the right --
are the same species.
They can interbreed.
Now, the dark one and the light one,
as you might expect,
do better in different types of environments.
This color characteristic
varies, of course,
and in some environments
it benefits the organisms
to be light or to be dark.
In other environments,
that same characteristic
may be detrimental to the animal.
So, these peppered moths
provided a classic example
of how characteristics can vary
with environment,
and how populations of a particular species
can vary.
So, this was noted
particularly in the industrial revolution.
At that time,
we went from manufacturing
using people
sewing or create objects
to using a lot of machines
to make products.
With the use of machines
came the use of coal,
and with coal came soot,
or pollution in the air.
Now, with that soot and pollution,
you could imagine that structures in the environment,
like trees,
would become darker,
and the peppered moth populations
changed in order to accommodate that.
And the darker morph
of the peppered moth
survived better. Right?
It was better camouflaged
against potential predators in the environment.
When the environment cleared up
and pollution decreased,
the tree barks became lighter
and the lighter version of the moth
actually survived better.
So, we can see variation
in the characteristics in a population,
even over this short amount of time,
and due to a human-induced
artifact in the environment,
this pollution from coal.
Now, just to show you how striking
this difference can be in the camouflage
of these moths on trees,
we can see some here.
So, here's our dark morph and our light morph,
and if we look at this tree,
we can see both the dark morph
and the light morph.
Here's the light one right down here,
and you can see it better camouflages
against the light bark
in this healthy tree.
The dark morph stands out against that light tree,
expect in this area over here,
where it's against this injury to the tree,
which shows up darker.
Another example in variation in populations
that we've probably all had experience with
is in bacteria
and the treatment of bacteria with antibiotics.
So, when we go to our doctor's office
with a bacterial infection,
we're prescribed antibiotics,
medicine to kill those bacteria,
and doctors are often very specific
about the need to take that medicine
over a precise time course,
and in particularly they say,
"Don't stop the medicine early.
You have to take the full course of medicine.
Even if you're feeling better,
take the full course of medicine."
It's important to do that.
Why is that?
It's because of the selection
that's acting on the variation in the population.
So, when we have a bacterial infection,
the species of bacteria
that's in our bodies
may have lots of variants to it,
and this is shown in number 1 on the left.
They might vary in aspects of their biology,
including how strong they are,
how resistant they are
to antibiotic medicines.
If we treat them,
shown in point 2 over here,
but we don't treat them long enough,
which are the bacteria
that are going to survive?
It's going to be the ones that are the strongest,
that are the most resistant
to the medication.
So, if we don't kill them
and we stop taking the medicine,
they'll be able to multiply
and will take on a larger part
of the population
of the bacteria.
It's not unless we kill them all
that we can prevent those resistant bacteria
from then multiplying
and becoming a problem
for our antibiotic medications
down the road.
So, I've shown you several examples
of how populations of a species can vary,
whether it's peppered moths or bacteria,
but how do we go from that
population-level variation
to the evolution of new species?
This is called speciation,
and in general
what happens is that populations
of a species
will be separated
and unable to interbreed,
and if they're separated
for a long enough period of time,
when they come back together
they may not be able to interbreed,
and then we would call them
different species.
One of the ways
that interbreeding is prevented
is through geographic isolation.
One of the students in my lab,
Andrew Trandai,
actually helped me out
by developing this hypothetical example
that I'm going to show you
on what a speciation event
might look like,
so I have to thank Andrew
for all of the images
that are coming up in the next series.
Okay, so in our hypothetical example,
what we're looking at is
some rodent squirrel-like animal
in an environment
-- one species --
all together as one population.
So, how do we separate them
and get new populations to evolve?
Well, in Andrew's example, here,
we have flooding
and an aquatic barrier
that these animals cannot cross,
so effectively
the population in the trees
and the population in the sand
are separated now
and will be evolving independently.
Over time, if we look at each of them,
we may see differences
being incorporated
into their biology.
Just superficially,
we might see the animals
that are in the forest
turning a different color,
other aspects of their anatomy
might change
to live in the trees.
On the opposite side of our river,
we may see the populations
that are in more of a sandy desert environment
change coat color
to match that environment,
or change size
to better adjust physiologically
to this drier environment.
Then ultimately,
once these differences have occurred
over, again, a very, very long period of time,
through evolution,
what would happen if the river dried up
and these animals
were able to come back together?
Well, they might come back together
and be able to interbreed,
but they may come back together
and not recognize each other
as the same species,
and therefore,
even though they're together
in this environment,
they would not interbreed
and their independent characteristics
would be carried on
from generation to generation
in those species.
So, that was an example
of geographic isolation,
and the biggest example of geographic isolation
happened about 200 million years ago,
when Pangaea,
which was this big super continental landmass,
broke apart to give us
the different continents that we know today.
So, South America and Africa
broke apart from North America and Europe,
and those continents
moved and separated around the globe.
With that separation,
the species that were together
prior to this breakup
then became separated,
and so if we look at species
that are in Africa versus South America,
for example,
we can see animals that
perhaps came from the same lineage,
but now are very, very different,
and are in fact different species.
Okay, so we've talked about this
process of evolution
and how it can occur.
What if we want to understand
the evolutionary history
of the animals that are
alive on earth today?
Well, we have to use a different set of techniques
to do that.
Here's just some of vertebrate diversity
and, as I said at the beginning of the lecture,
we also have lots of plants
and invertebrates and insects.
So I'm just showing you a very small part
of biodiversity here.
How do we figure out,
with animals so diverse as these,
how they're related to one another?
And how they evolved through time?
Well, we can take
a very simple example
of how we construct our own family trees
over very short time periods,
over several generations, say.
We research our genealogy,
we use birth notices and death notices,
and we recalled history
from our parents or grandparents,
and we can use that
to construct relationships
among our relatives and ourselves.
This is a really interesting family tree
that's on the wall of a Czech castle, actually,
and shows the relatedness
of this family,
going from a founder
down at the base of the tree, in the trunk,
up to the descendants at the top of the tree.
So, if we take a hypothetical example,
again,
of building a family tree,
and we start with
this family of green-ish and blue-ish,
big-eared and small-eared organisms,
and try to construct how they're related,
we can just look and see how family trees
are organized.
So, here I've taken that population
and put them onto their tree
-- that I made up --
and we can see that they're related to one another.
So, the individuals
that are connected at the first branch
are siblings.
They have the same parents.
If we move back in the tree,
we're looking at the different common ancestors
of these individuals.
So, if we go back,
these groups that are bracketed
in the orange boxes
are shared pairs of grandparents,
so they'd be cousins.
And if we look down near the base,
we can see that all of these organisms
share a pair of grandparents.
Now, because we're in recent history
and we have all sorts of ways
to record our history,
we may even know what these grandparents look like,
what our common ancestors of us,
and our sibling, and cousins, look like,
and I've reconstructed them this way.
If we look at at a group of animals
that's as broad as fish and mammals
and amphibians and reptiles, though,
we don't have that record,
to know what those common ancestors are
or what they looked like.
We have to use other types of approaches,
called phylogenetic approaches,
to basically try
to reconstruct the common ancestor
and how those species are related.
So, if we take this set of vertebrates,
this small number of animals,
and try to put them on a tree,
this is what it would look like,
and this is based on lots of peoples' research
over many, many years,
and I'll run you through it quickly.
On the far left,
we have the base of the vertebrate tree,
and these are lampreys,
these are animals that don't even have, really,
jaws.
They have these suction discs
that rasp and grip onto other species.
As we move up the tree,
we get into things like sharks,
and skates, and rays,
that have jaws,
but they have a cartilaginous skeleton.
When we move up yet again,
we get to the bony organisms
that include the fishes,
shown with these anemone fish,
the third image from the left,
and then we get up into the tetrapods,
that include amphibians,
reptiles, birds, and mammals.
Now, how do we construct
this kind of tree when
we don't have these detailed records
that we have of families?
Well, we do it by looking at
what characteristics these organisms share
and what characteristics vary between them.
There are lots of different types of characteristics
that we can use.
So, one of the features that we look for
when we're looking at shared characteristics,
or similarities and differences among organisms,
are anatomical features,
things like the shape of bones
or where sutures
-- where bones connect to one another --
or where we see holes through our skull
or other parts of our anatomy.
Bone and other structures
from the body
provide really nice characters
that we can use to try to figure
the relatedness of organisms.
In addition to using anatomical features
to try to understand the evolutionary history
of organisms and their relatedness,
DNA is now also
providing a really powerful way
of generating characters
to try to understand
how organisms have evolved.
In particular, we can compare a single gene
among different organisms,
different animals and species,
and see how it varies and how it's similar,
and look for changes in that
organization of the gene itself
that might give us signals
about how close a species is
to another species
and the relationship among them
and to different species.
Now, another set of data
that's been useful in understanding evolutionary history,
of course, is fossils.
They're really important.
Now, fossils provide information
about when and how features arose.
They won't, though,
provide the common ancestor.
It would be very unlikely
to actually dig up a fossil
that gives you the exact common ancestor of a species
but, nevertheless,
what they can provide us,
how they can ground our understanding
of when an organism
or particular elements and characteristics
of an organism arose,
is incredibly important.
So, to summarize
our introduction to evolution
and some of the major points we've talked about...
first, evolution is change
in the heritable characteristics of organisms
from generation to generation,
descent with modification
as proposed by Darwin.
Variation in characteristics
allows some subsets of populations
to be selected for or against.
And selection can cause change
in the characteristics
that persist in a population,
and this can allow for populations to diverge.
Reconstructing how the diversity of organisms
evolved
involves making trees,
or these phylogenies that I talked about,
that show different organisms
are related to one another.
And phylogenies, though,
depend on identifying characteristics
that are shared between organisms
and that can suggest their common ancestry.
And, again, we can get those characteristics
from morphology, from genes,
from all sorts of different sources.
Thank you.