Okay, so if I were to come into a room of
students and ask them all to describe for
me, or define for me, what is meant by the
Darwinian Theory of Evolution by Natural Selection
in four words or less I could pretty much
count on everybody scribbling out the same
answer.
It would look something like this.
And that's all well and good.
I mean, if you ever need to summarize the
idea without really demonstrating that you
know anything about it this would probably
be okay.
But there's a problem with this.
I mean, if I were arguing against the creationists
and they would point out that the whole core,
this whole definition of evolution by natural
selection was a truism or a tautology.
I don't know if you're familiar with this
term.
So the concept in philosophy of a tautology
is something that is, it's completely meaningless.
Tautology basically says that you're saying
the same thing over again.
If you turn the lights out in a room it gets
dark because dark is kind of like, defined
as the absence of light.
So of course if you turn the lights out it's
going to be dark.
So I mean, if you say something that is so
obvious and is so redundant that it has no
meaning then that would be a tautology.
And if anybody were to demonstrate for me
that this idea of survival of fittest is a
tautology then it would be basically be a
pretty destructive argument.
Okay.
And it's not that difficult to do that.
Okay.
So, I mean, if you say for example if you
define fittest, fittest actually means those
individuals in the population who survive,
then the survival of the fittest concept turns
into survival of those who survive which is
basically a completely empty and meaningless
sentence.
So the problem is not really one of the Darwinian
model being based on a tautology; it's simply that
that you don't convey the full meaning of
a pretty interesting theory in four words
without getting some significant meaning.
So I guess what I'm trying to say is that
survival of the fittest is a pretty poor way
of depicting the Darwinian model of Evolution
by Natural Selection and we want to just start
start off by doing a much better job, okay.
And we want to distinguish the concept of
evolution by natural selection with the actual
part that's natural selection in its own.
I like to make the following argument which
is that if you have these three conditions
there will be some evolution by natural selection;
there's no way around it.
It's not, can evolution occur or might evolution
occur?
No.
If you have these three conditions evolution
will occur.
If you're lacking any of these conditions
then evolution will not occur.
And so it's a really, this is a logical argument
and I think you guys are old enough to be
able to appreciate the logic behind this.
And so the three conditions are as follows.
The first one is that there must phenotypic
variation which basically means that there
has to be differences in the elite organisms
within the population.
If you start off with every individual in
a population being exactly the same then there's
no opportunity for selection to favor some
over others and therefore there would be no
opportunity to change.
Okay.
That was pretty easy.
B: Selection has got to favor some of those
phenotypes.
Remember, we've got phenotypic variation and
there's some phenotypes that are different
from others.
Some of those phenotypes have got to be favorite.
They have to have a greater success in survival
and or reproduction.
So phenotypes survive or reproduce with greater
success.
That's basically the natural selection part
of it.
If we have some phenotypes surviving or reproducing
with great success, that does not necessarily
mean we're going to have evolution.
In order for that to be actually the outcome
we have to have a third condition.
And that third condition is that a phenotype
must be heritable across the generations.
We have to have the offspring resembling the
parents.
If an offspring has a particular phenotype
and it's not related to genes or there's no
way for that to be passed on to the next generation
then there's no way for the population to
look different in the next generation.
Okay, so these three conditions in place -- you
know, organisms varying, and then some of
those variable types having greater success
than others and surviving and reproducing,
and if the offspring of those survivors and
reproducers have similar phenotypes to their
parents then across one generation the population
will look different.
Okay.
If we have all three evolution by natural
selection will occur and the population in
the generation of offspring will be different
in appearance from the population of their
parents.
Okay.
A great place to continue this discussion
is with these finches that were noted by Charles
Darwin.
And when Charles Darwin went to the Galapagos
he found some birds that looked like regular
finches, the ones he recognized back from
England, he ran into some birds that looked
like grosbeaks which are kind of a bird
that has a really large massive bill and
feeds on nuts.
And he had other birds in the Galapagos that
looked like wrens.
Wrens have these pointy beaks and the pointy
beaks allow them to poke into little holes
and to dig out insects and little grubs and
things from little crevices.
Now, when Darwin got back to England he basically
found out that none of these were finches
and grosbeaks and wrens -- well, actually
the finches were finches but this was -- but
these guys over here, the grosbeaks, were
actually finches that looked a whole lot like
grosbeaks from the bill morphology but if
you look at the rest of the animal, if you
were actually able to look at the birds when
they flew, these guys were clearly finches
that had grosbeak like bills.
And the wrens were also finches and here we
have the story of Darwin and his Galapagos
finches.
And basically the story that Darwin came up
with, the explanation that Darwin offered
for this scenario was that at some point these
islands, the Galapagos, which are in the middle
of the Pacific Ocean were colonized.
They originally didn't have any birds on them
at all and they were colonized by finches
and over time what happened was there were
these resources, these larger seeds and nuts
that the finch's bills, the original finch's
bills were not terribly well equipped to break
and so those birds with larger, more massive
beaks were better able to break those resources,
those larger seed resources.
And, over time, they became more adapted to
using that resource of larger seeds and nuts
and as a result they ended up with these grosbeak-like finches.
And other populations of finches, those birds
that had smaller bills, bills that were thin
and pointy had a greater advantage in fishing
out the resources of little insects that were
in crevices and that's basically how these
wren-like finches came about.
Anyways, that's the Reader's Digest version
of the story and I want to just kind of depict
with you, think about well, how that plays
out in terms of our earlier slide with those
three conditions that are required for natural
selection to result in evolution, okay.
So let's think about the evolution of the
original finch into this grosbeak like form.
And here's an important concept for you.
Okay.
So we have this way of depicting phenotypic
variation as a bell-shaped curve or a normal
distribution which basically means that we
go out into nature and actually measure things.
We can measure the tail length of squirrels,
you can measure certain kinds of behaviors.
What we typically find is that when we measure
a phenotype, phenotypes over here on the bottom
axis might be z for phenotype.
We might have some individuals that are extremely,
have got extremely low values, some individuals
with extremely high values, but those are
rare in the population.
The majority of the population tends to be
really close to the average and this is called
the mean.
The mean value of z, okay.
So in a typical finch population might have
birds with kind of like regular finch-sized
bills over here.
You might have some birds with slightly larger
bills, and some birds with slightly smaller
bills.
And there's a range, okay.
And so we've got the birds with the medium-sized
bills having the greatest frequency.
That doesn't mean they're the best ones, it
means that they're the most common ones, right?
And these really large-billed birds, they're
very rare.
The small-billed birds are equally rare.
And so that's our phenotypic variation.
Now, what we're saying is in the story of
the evolution of those grosbeak or larger-billed
finches, because the food resources that were
available were these large nuts and seeds
these birds on this end of the distribution
did really well.
These guys over here did very well.
These guys on the other end did very poorly.
So these guys had bad luck on this side and
they might have died out at a higher rate.
They might have had poor survivorship because
they got not enough food, they didn't get
enough food and they were eaten by predators.
And these guys over here had plenty of calories.
They were able to feed their young, escape
the predators, and they were successful in
surviving and reproducing.
Okay.
And so, that covers conditions one and two
of our story, right?
First of all, we have phenotypic variation,
some are -- they're different from each other,
and now we've basically shown that we've got
selection taking place where some of the phenotypes
have better survival than others.
Now the story goes is that, if we have the
phenotype being inheritable those birds with larger
bills are going to have offspring with larger
bills and we might come back in the next generation
and we would see, well, the offspring of these
birds that are here are going to have somewhat
larger bills relative than we had in the previous
generation.
Basically, the phenotypic average will have
moved from a mean over here, and average over
there, to a mean over there.
The whole population has shifted to the right
because of this event of natural selection.
Okay.
So yeah, I mean, this movement from there
to there, that would be kind of like our evolutionary
change.
And that last condition of heritability of
phenotype is required for there to be a change.
Now, that's the basic story of natural selection.
What we're going to do in our laboratory is,
it's going to seem a little bit weird, that's
because it's legitimately very weird.
And we're going to do this thing where instead
of, you know, doing what would be logically
sensible which would say, okay, we're got
a phenotypic axis and we've got variation
like this, our lab is going to be kind of
like a histogram, right, where we're going
to have different implements or a population
instead of being birds with short bills, birds
with medium bills, birds with long bills,
we're going to be kind of like birds because
we'll be picking up resources but instead
of having that continuous variation of different
values of bird size, we're going to have maybe
chopsticks over here, chopsticks, we'll have
a fork, with a spoon, we'll have a knife,
a tongue depressor, tweezers, I'm not sure
what they are, I'd have to read the laboratory
again.
And so instead of having a population with
a variation that's continuous like small beaks,
middle-sized beaks, and long beaks, we're
going to have a population of birds in which
the variation is really kind of weird where
some of the birds are using chopsticks to
pick up their foods, some of the birds are
using forks, some using spoons, some using
knives, tweezers and tongue depressors.
Right.
But the same idea applies.
I mean, even though we're not depicting variation
in the same way we should be seeing maybe
some differences in the bird's abilities.
And you guys are the birds and your abilities
as a population to pick up food resources
using different implements.
Okay.
And so what we're going to be doing is tracking
the success rates of the different implements.
And basically what's going to happen is that
it might start off with an equal number of
all of these different implements and after
one generation we might find out that tongue
depressors did really well.
These guys had a great amount of success.
These guys did really well and the chopsticks
did really badly, and the spoons did really
badly, and the forks did pretty well, and
the knives did pretty badly, and the tweezers
did sort of good.
And so basically, if we started off with a
population that had an equal number of the
four -- sorry, the six implements -- -- 
we might see these guys go down, they would
become less common.
These guys would become maybe a little more
common.
These guys would become less common; remember,
because they're not doing very well.
These guys would become less common.
And these guys would become far more common.
And these guys would become maybe about the
same because they're kind of indifferent.
And so basically, the population has shifted.
It has evolved from the original phenotype
range where you had equal number of all six
phenotypes, all six traits, to one which we've
got an unequal distribution with more tongue
depressors than everybody else.
Okay.
And then starting from this point, basically
now that we've got a new population with more
tongue depressors than everybody else, we're
going to do the same thing.
We'll put you out and you'll be collecting
the food resources and we'll find out, well,
let's see what's going to happen.
In the second generation maybe the tongue
depressors will do really well again, maybe
the forks will be doing really well the second
generation, and everybody else will be doing
poorly.
So if the tongue depressors do well it can
make their numbers shoot up and we'll end
up with a larger number of tongue depressors,
maybe the forks are going to be increasing,
and everybody else is going to be doing even
worse.
Okay.
So, this is kind of like the way that our
laboratory is going to work.
We're going to be simulating natural selection.
I think, for me, the hardest part about this
is to think about this kind of variation where
you've got your qualitatively different implements
-- I mean, as a person who has thought a lot
about evolution by natural selection, this
type of variation is not a very good representation
of nature but it does kind of allow us to
do our simulation and get the results that
we'd like to demonstrate for the class.
So we're going to be tracking, I think, three
generations of natural selection on these
implements.
We'll be talking about the results.
At the same time, we're going to vary the
quality of the food resources, like, we'll
have green beans that are worth four offsprings,
and green with black spots are worth eight
offspring and -- I don't remember what the
values are but they're written there in your
lab book.
Okay.
Our objective here is for you to have maybe
more hands on personal understanding of how
this process of natural selection can give
rise to evolution, and here we mean evolution
by a population's composition changing from
one generation to the next.
