- [Instructor] Okay, evolution.
- One of the most highly
controversial topics
of biology, yet, one of the
key to understanding ultimately
what creates the great diversity
of life on this planet.
So when we talk about evolution,
a lot of it ultimately depends upon
understanding the fundamental basics.
'Cause a lot of times when you have polls
and asking if people accept evolution
and things like that, most of the time,
they're not really asking the questions
that would get the response
that we're actually looking for
in terms of what are the
principles that drive evolution
and what is it actually?
So one of the things that
we're gonna learn today is
what are some of the things
that are so well established
that we understand them and
we call them principles.
And then we'll look at what
the theory of evolution
ultimately tells us regarding
the diversity of life
on this planet.
Now, one of the misconceptions
that people tend to have
is what evolution is and what it isn't,
which is why I like to start
off with this statement.
Now, this site National
Center for Science Education,
their goal, they're not a government site,
in fact, they're just kind
of a private organization
that does get some funding,
but most of their endeavor is
to essentially let people know
what the science is regarding
some of the more controversial topics.
They started off with evolution.
They're now delving into climate change
and things of that sort to
to help people really see
the science and kind of weed
through a lot of the opinions
that tend to mix up people's
understanding of these theories
as well as principles.
So this is from their website.
I really like how they phrase this
because it gets kind of the heart
of some of the controversy, not all,
but some of the controversy
regarding evolution
to be able to help people
understand really what it is
and what it isn't.
So I'm just gonna kinda paraphrase.
You can read this obviously here,
as well as on this website,
but one of the things I wanna
emphasize is it explains
why there's so much diversity
of life on this planet,
but it is not a theory of origins
about how life began on this planet.
In fact, if you read very
carefully in any biology textbook,
you'll find that there
are a number of hypotheses
about how life began,
but none which we've
actually settled upon.
There are some that are more
well-accepted than others,
but they're still debating on how life
essentially began on this planet.
So that's one thing that
you need to understand
is that evolution is not
a theory of origins, okay.
It ultimately looks at how you have
such a immense diversity of life,
and how we got to this point.
So ultimately, it looks at
the similarities of organisms
primarily through the genetics,
'cause as we've been
learning in the last lecture
about how when you have offspring,
the offspring are a
combination of the genetics
of the parents and how a lot of variation
is created by crossing over
an independent assortment.
We see that over time, these
same biological processes
are essentially what give us
this great diversity within species.
I mean, look at the human
species alone, everybody,
all human species on the
entire planet only differ
by about 0.1% in their genetics.
So we're very, very similar to one another
because we're part of the same species.
And we look at some of the
principles that ultimately drive
changes in the species phenotypes
as well as their genotypes.
And that's why we spent so
much time in this last lecture
talking about those because that's where
this understanding of what evolution is
really comes down to.
Now, the principles, remember
principles are the facts
within the theory that
ultimately are more well-defined,
the principles that we're
gonna study for this are
everybody knows natural selection,
but this is only one of
five different principles
that actually drives evolution.
And it's not always the
strongest driving force.
Sometimes sex matters
more in some scenarios.
All organisms have to do is worry about
havin' sex with one another and that's it.
Everything else is provided for.
So what a wonderful life.
Now, mutation symbiosis,
gene transfer, genetic drift,
these are some of the other principles
that we're ultimately going to look at
and how you get such a diversity.
Let me give you an example.
A lot of times when people look
at cauliflower, and cabbage,
and Brussels sprouts, as well as broccoli,
and things like that, you might think,
well, yeah, these are a great
diversity of different plants,
different vegetables that we like to eat.
In reality, they all come
from the same parent plant,
the mustard plant.
And so, we'll show how
some of these processes
select for certain
characteristics and traits.
And then how, when we
start getting involved
it no longer becomes natural selection,
it becomes what we call
artificial selection,
which has happened quite a
bit, since we've been here.
Now, one of the big
controversies of evolution
is the creation evolution
continuum so to speak
is what they call it.
And this is on the same
website that you could go to,
to be able to look.
And they pretty much delineate
every step on this spectrum.
Now, the second thing that I want to
ultimately help you understand
is it's not a dichotomy.
What I mean by dichotomy is
you're either a creationist
or an evolutionary biologist.
There is no like one side of
the line versus the other.
In fact, there's a huge
spectrum of overall belief
and acceptance that they kind
of put on this overall scale.
Now yes, a lot of times when
people think of evolution,
they think of the scientists
that are more on this end,
the atheistic evolution and regard,
but there are actually fewer
than you might think of these.
There's a lot of individuals
that are kind of more here
in the middle or what not.
Now, I'm not gonna go
through each one of these,
but typically the way
that they outline this
is on the one end of the spectrum,
where you have what we
call the flat Earthers,
are individuals who truly
accept that the Earth is flat
and don't look at the scientific
evidence to the contrary.
So their idea is that the farther down
you are on the spectrum,
the less you accept
regarding certain scientific facts
and theories and things
of that sort and whatnot.
But that doesn't mean that
on this end of the spectrum,
you're a pure scientist and whatnot.
So you can read this on the webpage,
but ultimately I wanna show you that
not everybody falls into
either this category
or somewhere over here
where they still believe
that the earth is the
center of the universe,
which we know is not
and so on and so forth.
So it's not a dichotomy.
Ultimately there are levels of acceptance.
And one of the jobs that
we have as instructors
is to help you understand
what it is the science,
what is the theory?
What is the principles that drive this
and what is the evidence behind it?
So that you can actually
understand it better.
Because most of the times
the surveys that people do
out in public or whatnot,
don't really get to the
heart of what evolution is
and what it isn't.
Now, when we say Darwin most people know
that this is synonymous because just like
Watson and Crick and DNA
are kind of synonymous,
because of their discovery
and ultimate theory
and understanding the
structure and function of DNA.
Darwin was the individual
who ultimately published
and got the initial information out there.
Now since his time, there've
been a lot of scientists
who have continued to publish
and follow in his work,
just like in any other discipline.
There were other scientists
that were also working
on this same theory at the same time,
but never published and whatnot.
So it wasn't a new idea, so to speak,
in the sense that he was the only one
who was thinking about it,
there were many others who
were thinking about it as well,
but we give the credit to Darwin
because of his work and his endeavor.
Just like we give the credit
to Mendel regarding his work,
on the laws of inheritance
and things of that sort.
So, the theory of evolution,
let's first talk a little
bit about Darwin's background
and ultimately how he came up
with the theory of evolution
and what its evolved
to, good choice of word,
today, regarding the scientific facts
and what we've learned.
So he was what we call it
a naturalist of his day,
which is the equivalent
of today's biologist.
And he traveled a lot.
And in his travels,
especially when he got to
the Galapagos Islands, he saw
a great diversity of life.
Not a lotta people got to
see the diversity of life
because they tended to
reside in the same place
through most of their life.
There wasn't a huge amount
of travel back in those days,
like there is today.
And so ultimately, when he
got to the Galapagos Islands,
he saw that there were
these isolated communities
of organisms that were quite
distinct from one another
and found that the
environment in that area
had caused a certain
selection for these traits
in these particular species,
and of particular note,
he looked at what we call
Darwin's finches because
these finches showed
very prominent selection,
depending upon the food source
that was available to
them on these islands
and therefore which individuals survived
as a result because of the
structure of their beak.
Later on, we've discovered
that the main difference
between most all of these finches,
comes down to just a tiny
change in a single gene
that changes the overall
size and length of the beak,
that then makes it whether or not
they're able to get insects,
or whether they're able to get seeds,
or whether they're able to get any other,
whatever the food source is.
So here's what he understood,
is that the finches may have started off
as a very diverse population,
kinda like you would see
in any species today,
but when the environmental pressure is on,
meaning you start having this
competition for survival,
those individuals which have
the best-suited characteristics or traits,
and it's usually characteristics,
not just one characteristic,
but characteristics or traits,
that allow them to survive,
they're the ones that ultimately
passed those alleles on.
This is why we talked about alleles again
in the last lecture as well.
They passed the alleles on
and over time, those alleles become
the more prominent alleles
or popular, I should say,
statistically highest
alleles in the population
because they're the ones
that give the best chances
for survival of the species.
And this is where he came up with
one of the principles of evolution,
which is natural selection.
So I'm gonna go through this real quick.
And then I'm gonna show you
a video that illustrates
that same concept that I'm talking about.
Now, natural selection
ultimately describes the process
where the environment selects
for those characteristics
in a species that give them
the best chances for survival.
Now, sometimes the entire species dies off
because there is no
adaptive trait or traits
that allow them to survive
in the changing environment.
And in fact, that's one
of the biggest concerns
about climate change today
is if the environments
change too drastically
and the species don't have
enough variation to adapt,
we could see the collapse
of many ecosystems
and really disrupt a number of things,
including our food source.
So it is of major concern to
understand how these climates
are changing and what ultimate
effect they're going to have
because they are interrelated.
Now, he looked at overall
things that must be in place
in order for natural
selection to be able to occur.
Number one, and this
is why we talked about
sexual reproduction as well.
There must be variation in the species.
If you remember back from lecture 14,
when we talked about sexual reproduction
and how that gives them a better chance
for evolutionary, for survival,
it's because it maintains
variation within the species.
The more variation there
is the better the chances
the species has of surviving
when the environment changes,
because it pretty much always does,
or this very dynamic and
is pretty much changing
from century to century
millennia, millennia,
and the better suited organisms
ultimately survive those changes.
Now, the other thing that has to occur
is there must be some type of competition.
If there's no competition,
there's no natural selection.
So there must be a
competition over resources.
Otherwise everybody's just
like, hey, everything's fine.
Everybody's gettin' enough food.
Everybody's gettin' enough sleep.
They're not being preyed
upon, you know, predator,
prey relationships, this is also a dynamic
of natural selection.
So there has to be some sort
of struggle for existence.
If there is no struggle for existence,
like we'll show later on today
with the birds of paradise,
they pretty much just eat
and have sex all day long.
Which is not a bad gig.
But they still have evolution,
even though they don't
have natural selection,
really working on them,
they still have evolution.
So you're gonna see the difference
between what evolution is
and the principles that drive evolution.
Natural selection is a principle
that ultimately drives evolution.
So you get this struggle for existence.
Ultimately the individuals
which have the adaptations,
it's almost never just one phenotype.
It's always usually a conglomeration
of multiple phenotypes
that do this, but they
have the best adaptations
and that enables them
to survive long enough
to be able to reproduce.
And when they reproduce,
they pass on those alleles
with higher frequency
than other species that don't have
the greater chance for survival.
Ultimately over time, those
alleles become more common
and the phenotype of
the population shifts.
So that's really what
we're looking at here
when we're dealin' with
evolution is changes
in the allele frequency over time.
But natural selection
isn't the only principle
that could actually drive these changes
in the allele frequency.
Natural selection doesn't
have an ultimate goal.
Its goal is not to make
organisms more advanced.
Its goal is not to lead
to the perfect organism
that there ever was.
In fact, it kind of does
the opposite at times,
most of the time it
weeds out what's there,
but there's not unlimited
potential in every single species.
Which is why our fossil records show that
99.9% of the species that have ever lived
on this planet are dead.
Because ultimately things change enough
to where they're not
gonna be able to survive.
They do not have unlimited potential
to adapt to every circumstance.
So no gene pool as we call it,
which is the assortment of
alleles that a species has,
contains every possible variation to adapt
to every change in the environment.
Another thing that happens is sometimes
you just wipe everything out.
You get this indiscriminate
destruction that occurs that
there's no chance of survival
and you get these species
wiped out purely by chance
or some catastrophe or whatnot.
There's another thing, too.
Natural selection can't
weed out, everything bad.
In fact, there are certain things
that will never be touched
by natural selection.
For example, Huntington's disease.
It can't be weeded out
through natural selection
because it shows up after
reproductive success.
So things that may be harmful
to the individual's ability to survive,
but don't show up until
after reproductive success,
they can't be weeded
out by natural selection
because they don't kill the organism off
before they're able to reproduce.
So there are certain things
that natural selection can't touch.
And it's not designed
to advance the organism
to become more perfect or
more adaptable or whatnot.
It merely selects for
what's already there.
This is a key point that I also bring up
in one of my test questions.
Natural selection can only select,
that's where the name comes from,
for what's already in the
genome of the species.
That's all it can do.
All it does is select for what's existing
within the species genome,
but it doesn't add more to
the genome or, or whatnot.
Now, let's talk about some terminology
that's gonna come into play
and then I'll define
evolution you as I see it,
because when it's defined this way,
there's really little controversy
in understanding what evolution is.
Now, the gene pool is essentially
when you look at all of the genes
and their alleles in a species.
So for example, all humans
have the same genes,
but we don't all have the same alleles.
So when we look at our
gene pool we'll find that,
though we all have the same genes,
there's a lotta variation.
Remember alleles are
just different versions
of those genes, from hair
to eye color, to blood type,
to height, to intelligence,
to all these factors,
these are the alleles.
This is what we call the gene pool.
Now, when you look at the conglomeration
or frequency of the
alleles of that population,
this ultimately tells you
what is the most advantageous,
because the most advantageous
is gonna be in the highest
quantity or with the greatest frequency.
Meaning as you dissect down,
what makes a species survive,
you'll find that those alleles,
which come together to give
you very particular phenotypes,
those are gonna be most
prominent within the species.
Now, as I mentioned it's
usually not just one gene,
it's usually conglomeration
of multiple genes,
multiple phenotypes that ultimately
allow species to survive.
But that then brings us to our concept
of how we define evolution.
So this is how I'm gonna test you on it.
Ultimately, evolution is the
change in the allele frequency
of a population over time, right here.
So over time, due to
a number of principles
that we're gonna discuss today,
ultimately, any change in
the frequency of alleles
in a species gene pool is evolution.
Now some principles have
a very rapid influence
and change in allele frequencies,
others work much slower,
but by definition, any
change is evolution.
Now, sometimes we look at certain alleles
and wonder why they're
there in the population.
For example, sickle cell
anemia is much more prevalent
in populations in Africa
than anywhere else.
And cystic fibrosis is much
more prevalent here in the U.S.
than in most other places.
And there's a reason for that.
Even though these are
very problematic alleles,
that cause diseases, they've
shown that there is a reason
why they're with greater
frequency, because in fact,
in some circumstances individuals
which carry these alleles
actually have a survival advantage.
And this is exactly what we see
even in the human population today.
This is why when we look
at different populations,
even of just the human species,
we'll see evolution in play.
Now, let's look at how
this works for humans,
because we see evolution even today,
specifically natural selection in humans,
as a result of the environments
in which we live in.
So, some traits as we've talked
about are very problematic,
like sickle cell anemia,
cystic fibrosis, and whatnot,
but they still continue to be maintained
within certain populations.
So the question is, why do
harmful alleles actually persist?
Well, it comes down to this
heterozygote advantage.
Now let's give you a scenario.
This is why it's more prevalent in Africa.
Individuals that have sickle cell anemia,
ultimately die from the disease,
and therefore don't pass that on.
Now, there are a lot of
heterozygous individuals,
or carriers, in that environment.
Remember that in this scenario,
you have a normal allele,
which gives you the dominant phenotype,
which in this case is
not sickle cell anemia.
And you have the recessive allele,
which is the carrier of that
allele, or of that disease,
but they don't express that phenotype.
Over here, individuals who
are homozygous dominant
are selected against primarily because,
they have a higher rate
of death from malaria.
So what you end up seeing is
individuals that get the disease die,
individuals that aren't
carriers of the disease die.
And we know the reasons
but I'm not gonna go into
all the details of how
this works, but carriers
though they don't exhibit the disease
actually are protected against
these diseases like malaria,
and each one has their
particular strength.
For example, why is
there a higher frequency
of cystic fibrosis in the U.S.,
it's because carriers of cystic fibrosis
actually are protected against
various diarrheal diseases
like typhoid fever and cholera,
which we've had our share of in the past.
So this is kind of a display
of some of these heterozygote advantages.
Some of which we understand,
and some which we don't.
For example, carriers of Tay-Sachs disease
actually are protected
against tuberculosis
and we still don't know why.
But we see that situation.
Starvation, people with
non-insulin dependent
diabetes mellitus ultimately have
a protection against starvation.
Now again, these are
carriers of this allele.
Cystic fibrosis, we talked about cholera
and so on and so forth.
So, even fetal ketonuria,
this is a very problematic
disorder with an amino acid,
but it actually protects
against a fungal toxin.
So, these are examples of
natural selection today,
in the human species.
If you look at what we
call the allele frequency,
you would find that there's a
higher percentage of alleles
that are sickle cell, have
the sickle cell disease,
the recessive disorder,
in African populations
than in other scenarios.
And that tells us that the individuals,
which reside in Africa,
ultimately are undergoing
a different evolution
than you or I that are
living in a different area,
because of the environmental
constraints that are occurring.
Now, natural selection
isn't the only thing
that drives evolution,
but it is a major factor
in many scenarios.
Now, let me briefly talk
about the difference
between natural selection
and artificial selection.
Because artificial
selection has been going on
and continues to go on for a long time.
Natural selection is when the environment
chooses those traits which
are best-suited for survival.
However, when we start getting involved,
we don't always choose various species
for their survival characteristics.
A lot of times we choose
them for other reasons.
For example, when we breed dogs,
that's artificial selection. Why?
We're not breeding them
for their ability to survive in the wild,
otherwise we would have no chihuahuas.
Ultimately, we're breeding them
for their various temperament,
coat, color, size,
and things like that.
In fact, all dogs are
considered the same species,
even though there are hundreds of breeds,
they're still technically
the same species,
because they all originated from wolves.
And wolves and dogs are pretty
much canines or Canis lupus.
These are the species that they are.
Now, that's because of
artificial selection.
Now we've done this as
well with other organisms.
We've done this with plants
and that's where we get a lot
of these different vegetables
from the mustard plant,
where we have broccoli
and we have Brussels
sprouts and we have kale
and we have cabbage and whatnot.
They all come from the same parent plant.
But when they were
breeding them, they said,
"Oh, this one's got a
little bit larger area
where they're flowering."
And over time that became broccoli.
And they were selecting for another one,
which had some slight divergence of this
and that became kale
and so on and so forth.
So ultimately, artificial selection
is when we do the selecting
and it's not always for survival.
Many times it's just for what we prefer.
We've done this with animals.
We've done this with plants.
We do this with our livestock.
We do this with all sorts of things.
So if the attribute we're selecting for
does not coincide with natural selection,
that's when we can end up with
serious problems over time.
Because ultimately, when we
start selecting things out,
without thinking ahead as far as
what ramifications that have,
we can have entire ecosystems
and things collapse because of that.
I can't tell you how many
times we've screwed things up.
One of the big things that
we're dealing with today
is a problem with pesticide
resistant insects.
Because in the past,
we've sprayed our plants
with a bacteria that had a particular gene
called the Bt gene that was pretty much
toxic to the insects.
Well now, with the introduction of GMOs,
or genetically modified organisms,
as we've talked about in biotechnology,
these plants that we grow, the corn,
and the potato plants
and things like that,
have this Bt gene
artificially inserted into it,
and so it's hereditary.
And we've had these plants
for years and years.
Well, what we've seen over time is that
we have driven the
evolution by introducing,
the evolution of insects by
introducing these pesticides
into the genome of the plants.
Another thing that we're
dealing with today,
as far as antibiotic
resistance comes into play is
because of the use of
antibiotics within our soaps
and other types of things,
we're actually selecting for bacteria
that have an innate resistance
to these antibiotics
and that's what's being propagated.
In fact, we've got a
number of bacterial species
that are resistant to
most of the antibiotics
that we have today, and as a result,
many of the things that
we've used in the past
just don't work anymore.
And here's one of the reasons why.
When you go in for a checkup,
let's say you got strep,
you know bacterial infection or whatnot.
Ultimately, the bacteria
being all one colony
and being clones of one another
tend to have the same genetics.
Now, in some cases you can
get horizontal gene transfer
from other bacteria that
maybe have some resistance,
but usually those are few and far between,
where you have ones that may have
an innate resistance to that.
Most of the time when we treat
that colony of bacteria
with an antibiotic,
we're able to kill off 99.9% of them
and your immune system can
take care of most of the rest.
However, when you don't
take your antibiotics
for a long period of time,
what you end up doing is killing off
a good portion of these bacteria,
but you're leaving behind
a lot more and over time,
if you don't continue to
take those antibiotics,
those start becoming the more
prominent within that colony,
and you get sick.
A little bit later on you go back,
your doctor never took my class
and so he gave you the same antibiotic
and ultimately it's not gonna work.
So in those situations,
because of our introduction
of these antibiotics
into many of the things that we use,
we're driving the evolution
of these antibiotic-resistant bacteria.
And this is becoming a big problem today.
Now, another aspect of evolution
as we look at it today,
and this is the premise for a lot of the
science fiction movies that you see,
is when we have a plague,
like in the movie "12
Monkeys", or "I am Legend",
or anything like that, usually about 1%
of the human species survives
because they have an innate
resistance to that plague,
whatever the case may be.
There's been a lot of stories told
about these types of doomsday scenarios.
Well, there is some science
behind that premise,
even though it's a science
fiction or whatnot,
because due to the amount of variability
that's found in the human species,
there is such a great diversity
that there are always typically
gonna be some individuals
that have some innate
immunity to some pathogen,
to some virus, to some
bacteria, or whatnot.
And the same thing is true for HIV.
In fact, back in the day
when the bubonic plague hit,
there were individuals
which had the same mutation
that gives an innate immunity to HIV
that allowed them to
survive the bubonic plague.
So though they were
carrying dead bodies away
and moving them, they never got infected
because of this innate mutation.
Well, they survive and over time,
this became more and more
prominent within the population
because of natural selection.
And they found that this is
pretty much the same mutation
that gives them this ability
to not be infected with HIV.
Now, let me ask the question.
If we had the ability
to take this mutation
and change everybody's
genetics in the world
to try to eradicate HIV,
would this be a good thing?
Yes, I see some of you
saying yes, some say no.
What would it be?
Would it be advantageous
for our survival to go in
and change all of our genetics
and yeah, we've eradicated HIV?
Why wouldn't this be any good?
- [Man] Genetic diversity is better.
- [Instructor] Good. Why?
- [Man] Because we can survive
more changes in the environment.
- [Instructor] Okay.
So what other things are out there?
Maybe we've got the swine
flu, or the bird flu,
or somethin' else.
If we change the genetics
so that everybody's the same in that area,
we've decreased our ability to survive,
because like you said,
we've decreased our
diversity, our variation,
and that's the key to
understanding survival
because the more variation
we have, we may not have,
and you may wanna be the individual
that survived the plague,
but the more diversity we
have within the species,
the greater chances of
our survival as a species,
in that regard.
So it's not a good thing
to make everybody the same
in their genetics.
Again, that's the reason
why we talked about
asexually reproducing
species have a disadvantage
in terms of evolutionary survival,
because they're clones of one another
and they don't have that diversity
like sexually reproducing species do.
Now, microevolution and macroevolution
are pretty much the same thing,
it just depends upon how
much time has passed.
And ultimately, the principles
that drive evolution
on a large scale versus a small
scale are exactly the same.
So when we look at the fossil records
and we see the evolutionary
history of life on this planet
and its divergence and what we call
descent with modification,
it just matters how much time has passed.
Your book makes a distinction
typically between that time,
and that's really the only difference
between microevolution and macroevolution
is how much time has occurred.
We can easily quantify microevolution
because we can see
these in various species
in our entire lifetime.
Macroevolution, we tend
to have to go back to
the fossil records and models
and our understanding of biology today,
to be able to make those intuitive leaps.
And a lot of biotech today has allowed us
to actually look at the
divergence of species
and the relatedness of each
other based upon the mutations
that have been inherited over time.
And so this is what we call phylogenetics.
Phylogenetics allows us to see
how closely related species
are to one another, based
upon their similarities
and their alleles, ultimately
the variations that they have.
Like I said, human species today
is only a difference of 0.1%.
But, our closest
relatives, the chimpanzees,
ultimately only have a few
percent differences from us.
And the further out you go,
in terms of evolutionary relatedness,
the more differences
there is in your alleles,
in your genome and the like.
So, when we look at a
species, as I mentioned,
you tend to get this bell curve
of distribution of alleles.
The more prominent alleles
within the species tend to be
the more favored.
Now, sometimes we don't
need to know the reasons why
they're particularly favored
unless we investigate further.
Maybe the bees like the
purple flowers better,
and therefore they pollinate them more.
Maybe the predators, the
herbivores that live in this area,
don't like the pink flowers as much.
So they eat the white flowers
and the yellow flowers more.
Yeah and there's a number
of dynamics that could occur
to ultimately make those
phenotypes the more prominent.
But the idea behind this is that
when we look at the
distribution of alleles,
we'll find that the most,
the highest frequency of those alleles
is usually the most advantageous
for that particular environment.
Now, what biologists will
do is they will map this out
and actually quantify it using mathematics
to give us a percentage
of the allele frequency
of the population.
And when they look at
the changes that occur,
they can actually quantify evolution.
This is something that a lotta people
don't quite understand
is that you can measure
evolutionary change in a species
based upon mathematical statistics.
So, let's say a hundred
years later they come back
and there's been a huge change
and now most of the flowers are yellow.
We may not know exactly
what drove that evolution,
but we know evolution occurred
because ultimately the
allele frequency changed.
So there must've been something
that caused that change
and we try to figure out
ultimately what that is.
Now, if it's something,
like we've talked about,
in terms of climate change
that we can do something about,
then it's important we understand
what effect we're having on that,
so that we can preserve our ecosystems.
And that's why there's such a large drive
to understand these things
and make those changes necessary,
especially for our involvement.
Now, population genetics is
essentially the way to quantify
allele frequencies, okay.
And when we see shifts,
mathematical shifts,
in the allele frequencies
of these populations,
we know that evolution is occurring.
And this comes down to a principle
that came up by two scientists,
Hardy and Weinberg, essentially.
They came up with this equation
that ultimately illustrates
the relationship between the alleles
and the frequency in the population.
Now you've seen this before.
You may not realize that
you have, but you have.
You saw it in the last lecture.
Well, you're asking, well
why, how have I seen this?
All right, well, remember we
talked about dominant alleles?
And we talked about recessive alleles
and the relationship that those alleles
have with one another.
Well, if we substitute
the dominant allele for P
and the recessive allele for Q,
this is ultimately where
we get this equation.
Let's say that we cross
two heterozygous parents.
And what do we get?
We get 25% homozygous
dominant, 50% heterozygous,
and 25% homozygous recessive.
Well, let's change this.
So that now the A is P.
What's P times P?
P squared.
What's PQ plus PQ?
Two PQ.
And what's Q times Q?
All this is, is
illustrating the percentages
of individuals in the population
that are homozygous
dominant, heterozygous,
and homozygous recessive.
That is what this equation illustrates.
Now this is only for two alleles.
When you start adding three,
or more, starts getting huge.
And usually you'll use computers
to make some of those calculations.
But ultimately this is
the simplest form of it,
which illustrates the
distribution of alleles.
So, the letters P and
Q ultimately represent
the dominant recessive
alleles in a population.
And this is what Hardy and
Weinberg ultimately came up with.
This was the way to quantify evolution,
in looking at those allele frequencies.
So two PQ represents the
heterozygous individuals,
P squared represents the homozygous.
Dominant and Q squared represents
the homozygous recessive individual.
Now, Hardy Weinberg, the
Hardy-Weinberg equilibrium
isn't just about the allele distribution.
It also explains all of the
principles that drive evolution.
And this is, a lot of these people just
have never talked about
or don't understand it.
You don't just hear them in the general,
which is why I wanna
make sure you understand
that natural selection
is not the only principle
that drives evolution.
And we've talked about that
descent with modification
and the changes in the
allele frequencies over time.
Natural selection is
just one aspect of that.
So here is what we call the
Hardy-Weinberg equilibrium.
Evolution is always occurring,
it just depends upon how
many factors are in play
that determine whether it's
very slow, or very fast,
or somewhere in between, or whatnot.
In some scenarios, evolution
can be almost nonexistent,
but it is always occurring
in one form or another.
So if you don't have natural selection,
there are four other principles
that can actually cause
evolution to occur.
And this is where Hardy, Weinberg came up
with what they call the equilibrium.
Now, this equilibrium is
a hypothetical scenario.
It doesn't exist anywhere on our planet.
Ultimately, there is
going to be evolution,
but this is the .0 of no
change whatsoever that says
if all five of these hold true,
then there will be no evolution.
So why would we even talk about this
as a hypothetical scenario?
Well this gives us a point
to jump from, to say,
the more you deviate
from this equilibrium,
the more evolution is occurring.
So the more natural selection you have,
the stronger the driving
force of natural selection,
the more evolution you're getting.
The more mutations, the
more selective mating is,
the more evolution you're going to get.
The more gene flow you get,
or the smaller the population,
the larger evolution, or
the larger you will have
this effect of evolution occurring.
So, when they came up with
this equilibrium, they said,
here are the five conditions
that ultimately drive evolution.
So, when we look at it
from the perspective of
what are the deviations
or what causes evolution,
these are them right here.
These are the five principles
that drive evolution.
Now we spent a considerable amount of time
talking about natural selection.
So I wanna spend more
time talking about these,
in fact, on your quiz for this lecture,
most of your questions are going to be
on these driving principles
and how they influence evolution
in a number of circumstances.
So, let's start with mutation.
We talked about mutation
back in lecture 10,
regarding changes in the allele frequency.
What were some of the
mutations we talked about?
What are some of the ways
in which the DNA can change?
(student speaks indistinctly)
- [Instructor] What's that?
(student speaks indistinctly)
- [Instructor] Crossing over can mix
and match between homologous chromosomes,
but what is an actual mutation?
How do you change the DNA sequence
or the nucleic acid sequence?
I know it was a long time ago right.
You can get a point mutation.
What was that?
(student speaks indistinctly)
- [Instructor] When it switches one
nucleic acid for another,
one base for another.
And as we learned, this
ultimately can change
the amino acid sequence,
which ultimately can change the protein,
which can change the phenotype.
So that's one type of mutation.
Others are things like frame shift.
Remember, where you add
or take away nucleotides
and that ultimately can
cause massive changes
in the overall protein confirmation.
So ultimately, the variation
that you find in every species
has its origins in mutation,
which is why we say mutation
is the raw material for evolution,
because no other principle
can create new alleles.
All these other principles,
merely select for the alleles
that are generated through mutations.
So this is why we say mutation
is the raw material for evolution.
And there are many things that
can cause mutations to occur,
but ultimately that's how you
have different hair colors,
different eye colors,
different skin colors,
different heights, different blood types,
all these have their origins
in changes in the nucleic acid sequence,
which is why we say mutation
is the raw material for evolution.
Now, this is one of the slowest
driving forces of evolution.
Why? Because mutations are random.
They happen from various circumstances.
They're not selective a lot of the time,
they just change it indiscriminately.
And so when mutations occur,
it matters where and when
and all of these factors.
And it takes a long time for a species
to accumulate mutations.
Ultimately, without mutations
none of these other principles matter.
If you didn't have any variation,
then there'll be nothing to select for
as far as mating goes.
If you didn't have any variation,
then there wouldn't be any
changes in allele frequencies
due to migration, or
due to chance variation.
And then of course, there wouldn't be
any different phenotypes
in which natural selection
would be able to select for.
So, that's why mutation
is key to evolution.
Now, as I mentioned before
when you introduce a species
to a particular selective
pressure, be it environmental,
maybe we take an antibiotic,
which is an environmental
selective pressure
against the bacteria
that are affecting us.
The bacteria don't
respond in kind and say,
oh, we better start mutating faster
so that we can generate an antibiotic,
or a resistance to this antibiotic.
No, it happens too slowly.
So ultimately, the bacteria
either have the resistance
or they don't.
When you take that antibiotic,
if they don't have the
resistance, then they die off.
If they do have the resistance,
then they're gonna be selected for it,
and they can pass that on.
One of the devious things about bacteria
is what we call horizontal gene transfer,
where they can actually share
their antibiotic resistance
with other bacteria.
So though bacterias are
clones of one another,
they can share this resistance
with other bacteria.
That becomes very problematic,
because they don't have to evolve
new mutations all the time,
they just share what they've got
and that causes major problems.
Now, I've got a video, non-pornographic,
of non-random mating of
the Birds-of-paradise.
Now this is one of the
other modes of selection
that is as strong, in
some cases maybe stronger,
than natural selection itself.
Remember I told you that these birds
have nothing better to do than just eat
and have sex all the time.
Ultimately, non-random mating
has driven the evolution
of so many different species.
So what does it mean to be non-random?
Well, random mating means
that the individuals
are having offspring with anything.
There's no reason why
other than this one's ugly,
this one's pretty, this
one's big, or whatnot.
There's no reason why they're
mating with one another.
But that's the hypothetical scenario.
In reality, we're very
selective with our mates.
In most species, there's always some form
of sexual selection.
Even in plant species,
even though they don't have
the same dynamics as animals and whatnot,
there are certain features that make them
better reproducers than others.
And that is also non-random mating.
Now, gene flow, this is one of those
that's more situational
than anything else.
It doesn't really drive evolution
because really natural selection
and sexual selection are the
main causes of progression,
or I should say selection of the alleles.
However, gene flow is
technically part of evolution
because it allows for alleles
to be either taken away
or reintroduced into a population
from one generation to the next.
So, really all it is is let's
say you have two populations.
And again, all of these principles
are occurring at the same time.
Each environment's gonna have
its own natural selection.
The association with the
organisms amongst each other
is gonna have their own sexual selection.
And ultimately, if you keep
them separated over time,
they'll eventually
generate enough diversity
that they may eventually
become separate species.
Now we're gonna talk more
about that in the next lecture
on what's called speciation.
But, the more interaction
that the populations
have with one another,
the more alleles they'll have in common.
So, here's ultimately
what gene flow is about.
Let's say that in both these populations,
you have alleles A-B-C-D and E okay.
Just various versions of each
of the genes and whatnot,
and this one just looks at
one gene at a time or whatnot.
Now, let's say in these environments
that natural selection
weeds out alleles C and D,
and over here it weeds
out alleles A and B.
Again, you've got all of these
selective pressures going on,
natural selection, sexual
selection, and whatnot.
Well, what happens too sometimes
is each of these have their own mutations.
Let's say all of a sudden,
this one gets a new mutation F.
Now, when you take organisms
and they migrate away
and usually can introduce these alleles
back into the population, such as A and B,
and even bring new alleles
into the population, such as F,
and maybe in this new environment
F becomes very favorable.
And so all gene flow is, is it brings in
or takes away alleles through migration.
But let me be clear on this,
because this is a key point
that sometimes people make a mistake on.
It doesn't create new alleles.
The only principle that creates
new alleles is mutation.
Gene flow merely introduces
the alleles through migration
from one population to the next.
Now by definition, as we've
talked about evolution,
being a change in allele
frequency over time,
this is evolution because,
you're either reintroducing alleles
that were once weeded out
or bringing in alleles
that arose here through mutation,
but is being introduced here
through gene flow into the population.
Now, it may be that the natural selection
selects against alleles A and B,
if those selective
pressures are still there.
But by the introduction of
this allele through gene flow,
all of a sudden, maybe
this is the new sexy thing,
for sexual reproduction or
whatever the case may be.
But that's what gene flow's all about.
It essentially brings in
alleles through migration.
Now, genetic drift, this is highly related
to what we just talked about
in the the last lecture,
lecture 15, on the law of segregation.
And that's really what genetic drift is,
is the chance of which allele
is passed on from each parent.
So when we look at genetic drift,
this is essentially changes
in allele frequencies
merely due to chance.
Because as we know, when you
have heterozygous individuals
that pass on their alleles,
well it's a 25% chance
that the offspring will
be homozygous dominant,
50% chance that the offspring
will be heterozygous,
and 25% chance that the offspring
will be homozygous recessive.
So lemme give you a brief scenario.
In a large population, there
are so many individuals
reproducing with one another,
that the shift to one
allele or another randomly
doesn't really make that
much of a difference.
You don't statistically get the population
shifting towards the dominant allele,
or the recessive allele merely by chance.
And the way to illustrate this
is by looking at something like this.
So here's a scenario,
or several scenarios,
where we just look at the
dominant allele, the big A,
rather than the little A.
Well with 10,000 individuals
reproducing with one another,
these are just some statistical
scenarios of probabilities.
Notice very few of them,
if any, deviate that much.
So it's really just a 50/50 chance
on whether the big allele gets passed on,
or I should say the dominant allele,
or the recessive allele.
However, in extremely small populations,
these are extremely
susceptible to genetic drift.
So genetic drift is going on all the time,
but if the population
is sufficiently large,
you don't get evolution of a
species merely due to chance.
If the species however,
is extremely small,
meaning the number of
individuals in the population
that are reproducing is extremely small,
then you get profound
changes in the population.
Not because the allele is more favorable,
not because for sexual selection,
or for natural selection,
but merely due to chance.
So let me illustrate how this works.
Let's say that you have two parents
and that's what makes up the population.
We'll whittle it down to two individuals.
They have two offspring.
Well, chances are that at
least one of the offspring's
gonna be heterozygous.
It's a 50% chance.
Let's say then, that
they have a second child
and it's homozygous dominant.
That's pretty likely too,
because you're lookin' at
a one in four chance here.
Now the parents die off and
these two become the next
for that generation or whatnot.
What are the chances that they'll have
a homozygous dominant from this cross?
Let's look at that.
Is there any chance
that they're gonna have
a homozygous recessive individual?
No, it's basically a 50/50 chance.
It's very possible that
they have two offspring
and those are both their offspring.
Guess what happened?
Within two generations,
you've completely lost
the recessive allele and you now only have
that dominant allele.
That's genetic drift.
With small populations,
this becomes more prominent.
So, when you look at what we call
the Hardy-Weinberg equilibrium,
which is the no-change scenario, remember,
the ultimate no-change scenario
is that the population
is sufficiently large,
that it avoids these drastic changes
in allele frequencies
due to genetic drift.
So, genetic drift and
the law of segregation
are the same thing.
We've been talking about
this for quite a while now.
The law of segregation and genetic drift
are pretty much the same thing.
You can't get rid of it,
it's always gonna happen.
However, the equilibrium
or the no-change scenario,
the population's large.
When the population's small
that's when you start getting
more and more genetic drift.
It becomes more and more prominent
because of the small population.
Lemme give you some examples.
How do you go from a large
population to a small population?
Well there's a couple of ways.
Number one, you can have what's
called the founder effect.
This is when you get pioneers or pilgrims
that break off from the large mass
and reproductively isolate themselves.
And that's what happened,
when we had the pilgrims come
over, when we had the colonies
starting to form our country and whatnot.
And when we had pioneers
also come West and whatnot.
When we have these isolated
groups, then all of a sudden,
instead of having a large pool
in which to reproduce with,
you now have a very small pool
in which you have these
reproductive individuals.
So the founder effect is one of the ways
in which genetic drift
becomes more prominent,
because now you have fewer
individuals to mate with,
just like we talked about.
Large populations, very
resistant to genetic drift,
small populations, very susceptible.
There's another thing about
founder effect, though.
It doesn't have to be through migration.
For humans, it could be through cultural
or religious isolation.
We see this all the time with
various religious groups.
One of the more prominent ones
that we usually look at are the Amish.
The Amish have very
reproductively-isolated communities.
And we've looked at the allele
frequency of certain things
within the Amish community
and found that they
have a higher frequency
of some certain alleles.
Not because they're more favorable,
not because they give them an advantage
for natural selection or sexual selection,
unless you find multiple
fingers or toes sexy.
Polydactyly is one of those alleles
that is much more prominent in Amish
than in other groups, not
because it's more favorable,
but because you have this
reproductive isolation.
And we find this in lots
of different groups,
not just the Amish.
We find this in lots of
different religious groups
where they tend to isolate
themselves reproductively
to those of the same religion,
or the same culture, whatnot.
So that's the founder effect,
is where you get these changes
in the allele frequency
because there's fewer
individuals to mate with.
Now, the other one is more drastic
and actually more dire,
it's the bottleneck effect.
Just like a bottleneck is a
narrowing down of a bottle,
as you can see here, the bottleneck effect
is the concept that a
species that tended to have
lots and lots of
individuals has gone through
some catastrophic event.
Now this catastrophic event
doesn't have to be natural,
it can be manmade, for example,
we have caused the
bottleneck effect on bison,
on whales, on a number
of different species
because of our predation,
which is really what it is.
What happens is when you
whittle down the population
to just a few individuals,
sometimes just a few thousand individuals,
you have now made it so that not only
are there fewer individuals to mate with,
but you've decreased the
diversity of that species
by eliminating most of the individuals.
So not only do you have less diversity,
which as we know makes
it so that the species
has a less chance for survival,
but genetic drift is gonna
take those few individuals
and drastically cause massive changes
in the allele frequency,
because there's just not that
many individuals to mate with.
And this is one of the
problems we see today,
especially with the whales.
Is that because of the amount
of whales we've killed,
there are so little genetic diversity
that if their habitat changes
they're pretty much gonna
go extinct in these species
that we have killed over the years.
Cheetahs have undergone their
own reproductive isolation.
I mean, not reproductive isolation,
their own bottleneck effect.
In fact, they believe
that they've gone through
two rounds of bottleneck effects.
When they take genetics from cheetahs,
from the different habitats
that they have in the world,
even though they're
reproductively isolated
for these populations, their
alleles are almost the same.
There's such little genetic
diversity in these cheetahs.
And that's why they all
pretty much look the same
and have the same behaviors
because there's not that much
genetic diversity amongst them.
So, let me also be clear on this,
this is another mistake
that people tend to make.
Founder effect and bottleneck effect
are not the evolutionary principles.
They are not what caused
evolution to occur.
Let me be clear on that.
Genetic drift is the
evolutionary principle.
It is the change in allele
frequencies due to chance,
which allele you pass on, over time.
Founder effect and
bottleneck effect are events
that take a population from
very large to very small.
And that is what causes genetic drift
to have a greater influence
on the population.
So genetic drift is always in play.
If the population is sufficiently large,
then there's no genetic drift.
If the population is small enough,
then genetic drift becomes
more and more prominent,
as you can see.
Now we've talked about natural selection.
Talked quite a bit about it.
Let's look at what actually is doing
the natural selection, the selecting.
What are the factors that nature uses
to weed out those things,
which are not advantageous for survival?
Now, there are two main divisions
of natural selection processes.
There are the, what we call
biotic or the living components.
And then we have what
are called the abiotic
or non-living components.
So the living components are threefold.
There's competition for resources.
And this is what you see
with like the finches
that we talked about before.
They're competing over food
and the ones that have the beak
best-suited for that
food source out compete
the others of their species,
and they're the ones that survive
and pass those alleles
onto the next generation.
So competition for
these limited resources.
Predation, these predator
prey relationships.
This is where we see things like
camouflage, warning coloration.
There are some species
that have even developed
what we call warning mimicry.
Where they're not actually poisonous,
but they show these bright colorations.
Have you ever seen "Rio 2",
I'll give away the plot.
The frog's not poisonous.
Where this warning mimicry,
is that the animals
avoid these highly-colored organisms,
because that usually means
you eat me, you're dead,
because of the poison.
Now, there are many frogs
that do have actual poison
in their skin, and the animals
are well known to avoid them.
So predation, these
predator prey relationships
have caused a lot of evolution,
of not only camouflage,
but many other mechanisms
in which both the prey
and the predators are able to survive.
And then of course, parasitism.
This may not be as clear at first,
but a lot of times people will wonder,
how do parasites evolve?
Well, a good parasite is one that doesn't
outright kill the host.
Because bad parasites, or
ones that get weeded out,
are ones that kill the host
so rapidly by weakening them,
that they can't spread to the next host.
So in fact, parasites have
evolved over the years
to be able to feed off of the organism,
but not outright kill the organism,
not weaken them to the
point where they can't pass
to the next host and whatnot.
So these are all things that ultimately
are the biotic or living
components of natural selection.
Now, let's look at the
non-living, weather, climate,
temperature, moisture, these
are the environmental factors
that ultimately regulate also
a form of natural selection.
For example temperature,
some animals just can't live
in different environments.
They can only live within
various temperate zones.
Others have to live in
very moist environments
to be able to survive and whatnot.
And this is where climate
change comes into play.
Because as the environment changes,
some species might not be able to adapt.
And if those species are
key for the structure
of the stability of the ecosystem
and they go away, the
ecosystem will collapse.
And we're seeing this in a
number of different areas
around the world, due to that.
