just to reminder in terms of these
narrated presentations you will want to
go back through and look at some of
these slides in more detail just so you
can get the full picture as to what
these chapters are about as we go
through them during this presentation so
as we conclude our view and biology from
the semester we are finishing up with
three chapters on evolution and the
ideas we're going to see in these
chapters are ones that we have kind of
eluded to all semester especially going
back to chapter 1 and to talk to about
how evolution is a common theme among
among all biology so we're going to see
in couple 22 of they start kind of some
of the definitions as to what evolution
is what natural selection is and how
these different ideas kind of come
together and basically we've learned
throughout the semester so sort of not
first with evolution we can give it a
very simple definition simply the fact
that evolution is defined as descent
with modification so when you think back
to things like gaming production or you
think back to our idea of genetics the
whole idea there with our passing on
that information was trying to vary that
next generation so we saw the fact that
mutations can cause variation we saw
that in the recombining of chromosomes
or in say crossing over cook can lead to
variation each one of these things that
are things that we can look at that are
all coming under the whole principle
this is something modification we see
here a defined by Charles Darwin now
before Darwin if we look back just a
little bit in terms of kind of previous
ideas before evolution we comfortable
mark and Lamarque had an idea that is a
little bit similar to what Darwin
actually comes up with but with a Marx
principle it was based primarily on the
use or disuse of a characteristic so on
a little example the drops here we can
see in the marks principle that in the
first round of drafts we have very short
necks and according to the mark if that
draft stretches neck every single day
farther and farther and it acquired this
characteristic throughout its lifetime
and the next generation we
see the next even longer and then what's
standing what happening in the next
generation next generation until those
organisms were adapted to their
surroundings the problem was this is
that there's no actual evidence to
support Lamarck's hypothesis but with
Darwin's idea which kind of goes along
the same principles we're going to see
that in that population
not all giraffes have the same length of
neck and you're going to find that some
of those giraffes had a little bit
longer neck which gave them an advantage
over the other shorter neck giraffes
which meant that those longer neck
giraffes were able to live longer and
also reproduce more which were the next
generation we should get a longer neck
drafts they'll be introduced now because
of the characteristics that we can see
as variation generation by generation
you're going to see again a set of
giraffes went even longer next just due
to random variation throughout those
times and so this kind of accumulation
where we see the one that's more adapted
the environment surviving better and I
carry on the next generation and we're
going to see as a fact that these traits
themselves are not ones that we see are
inherited based on their acquisition but
the traits are we seeking inherit are
the ones are being the more benefit the
ones that hug to increase the chance of
survival for those organisms so when we
look at Darwin's idea with a
simplification one of the things we're
focusing on is the fact that an organism
is and gashing to its surroundings or
it's adapting to the environment and
this is actually best seen with Darwin's
finches and where the finches that he's
looking at you're going to see that in
every island in the Galapagos there is a
Finch with about the same body size but
the beak shape is drastically different
and each one of these Finch species has
adapted to the surroundings so that in
some cases where we've got a lot more
cactus put the cactus flowers as a food
source you get a define beak shape
that's a little bit longer if we've got
areas where was a lot more insect may be
found in the bark of trees you've got it
Finch with a much more narrow beak or if
you got an environment was a lot more
seeds present for as a food source you
have a much broader beef with a much
greater force to crack those seeds open
each one of these finches them if we
look far enough back in the evolutionary
history do come from a common ancestor
one that's right off the coast of South
America but as each one of these kind of
find their own habitat you're gonna find
that the beach shape itself kind of
comes along with it that adds McFly to
new areas or they start to overcome or
come into a new habitat you may not have
the right shape at the beginning but as
time goes by there's an adaptation to
meet those surroundings so a with
Darwin's idea about evolution you're
gonna find the here and never actually
coined the term evolution itself he
relies again on our definition which we
say descent with modification and the
way he sees his process work is actually
driven by the process of natural
selection and what's the other discussed
now it just looked a little later on
that this process is where those
organisms that have a more favorable
trait I got a more likely to survive
longer and hopefully reproduce more so
as we look at these ideas from Darwin
there's two things we want to look at
that are kind of very broad ideas form
first of all is our unity of life this
is actually one of the things that all
semester we keep going back to in the
terms of how do we define life and we
said that every organism out there has a
cell formation and we've got this
structure where you've got some kind of
DNA on the inside so we talked about the
membrane talk of the DNA in a very first
chapter that's kind of these unique
pieces these are items that we can see
as unifying all life on the planet but
as you have seen as we looked at
prokaryotes versus eukaryotes or even
among things like plants and animals
there's a great diversity that comes
with all of this unity allowing it
organism itself to match the environment
in terms of the adaptation now these
ideas where we see this unity and
diversity are best kind of shown and
what we call these evolutionary trees
which are basically hypotheses based on
what ancestors might have looked like
and how they have led to our modern day
specimens so in this little evolutionary
tree we're seeing not just the elephants
but we're also seeing what are called
the hyraxes and wheels called our
manatees now the tree is little
misleading
top these lines even though they look
like they're straight in fact it would
have the same kind of branching pattern
you're seeing here with all the
elephants
the reason we're showing them was a
straight line here is because we're
focusing primarily on the elephant's as
main focus but as we look at the other
things you can see that every little
node become from the evolutionary tree
these are common points in ancestry
where something in this case let's say
the mammoths and everything else they're
gonna share this one distinct
characteristic or one variable that was
different from this previous ancestor
when you're looking at everything all
the way down into the mammoths and
modern-day elephant you're going to see
that the mammoths did share a common
ancestor here but as you branch off into
our marm the elephants you're going to
see that again
not mammoths being on the outside of
that branching had a changing
characteristics whether or not this
little branch come off the elephants was
the fact of less hair production or
warmer climate adaptation it's hard to
say just being some of them are little
evolutionary tree here but you can see
that every single point is a point of
which they have diverged in some form or
characteristic with their ancestors
now one other thing we can look at with
this idea for evolution and the whole
adaptation is actually a process that
mankind has been doing for quite some
time and that's a process of artificial
selection and well artificial selection
what we're gonna see is the fact that we
can take a wild organism in this case
looking at this wild mustard and based
on things that we select for like leaf
size or maybe the apical or the very tip
bud being larger we're insane larger
stems we can produce these crops in this
case that are actually descendants of
that wild mustard which means that each
one of these organisms the kale the
cabbage the broccoli kohlrabi and
Brussels sprouts are all out to the
exact same species as the wild mustard
we have just modified them for our own
use their own benefit
same idea could save for all the dog
breeds all dogs even look very different
on the exact same species they all come
from a wolf-like ancestor so this idea
of artificial selection is actually one
thing that led Darwin down the path of
trying to describe a natural selection
but as he's doing this there are two
things we have to keep in mind is that's
two observations that he makes about the
world around us that's leaning him down
this path to natural selection as a
process driving the evolution and the
first thing we're going to look at is a
fact that any population you're gonna
find that every individual is varied in
some way so looking at the ladybugs here
as an example you can see all different
colors you get different sizes you get
the number of spotting different sizes
of spots those traits we think about our
inherited traits so we're not going to
have the ones that you acquire but ones
you are inheriting let mean the darker
one ones are more prone to produce
darker ones and next generation more
spots more spots next generation so
these are things you're going to see in
every population the other observation
he's gonna make is the fact that with
all these different species you're going
to find that typically the species
itself will produce more offspring than
what the environment can support
and that means that some of those
offspring are not going to survive and
some of those are not going to reproduce
now for those two observations we can be
used on the path here basically which
driving Darwin to the idea of evolution
and that's the fact that with the
individuals where you've got this
variety of traits that are inherited if
some of those traits give a higher
chance of surviving and in turn a better
chance of reproducing then you should
find that those organisms will usually
leave more offspring than other ones who
don't survive as long or don't reproduce
as well this also means that when you've
got this environment as come a limiting
factor that the environment can't
support all those organisms I'm trying
to get competition that the ability for
some of those organisms to actually
survive reproduce more should lead to
the accumulation that those traits that
made them more beneficial or favor them
in that environment or oxygen accumulate
generation after generation
now these traits were looking at in
terms of variety
remember that mutation itself is the
only way to produce some kind of new
trait the ideas of sexual reproduction
would gametes and using meiosis that
only led to the reshuffling but
reshuffling is just as important as
having mutations because when you
reshuffle the alleles you might produce
a offspring that is actually have a
better or condition that the combination
of all those existing traits that were
there combined into one unique set that
actually favors that one over everybody
else in terms of surviving generation by
generation again the idea here with
these two inferences is the fact that we
have a better chance of surviving
reproducing if we are matched to our
environment and that's the whole thing
we're going to see in terms of these
populations as you look at evolution
with natural selection
now we look at natural selection and
this is the process behind evolution you
will see that natural selection is
essentially the environment
favoring some characteristics over other
or some traits over other ones there or
the whole idea of natural selection is
again increase in the adaptation we want
the organism to match their surroundings
or match their environment and we can do
that by making sure that those organisms
survive longer reproduce more and pass
on more their genetics to the next
generation now this idea that we are
selecting those individuals with
favorite traits is also one of the
things that adds environments change you
will find that new adaptations are being
favored which event you could lead us
down the path of a new species so when
we think about these two ideas of
evolution and natural selection combined
we're gonna see that as individuals we
can evolve it's a population that
actually evolves as individual though
you can actually go through an
experience natural selection because the
environment can favor you or not favor
you and if the environment does favor
your condition then there's a greater
chance that those traits will increase
in the population over that next
generation or the directional range and
I asked that or in the next hundred
thousand generations but that idea that
we have the individuals leading to this
evolution of the population is all based
on those set of genetics that you are
dealt as an individual but everyone is
allocations remember is going to vary
with the environments which means that
even though we might think that ideally
natural selection could lead to its
evolution of the perfect population the
perfect type of species that's based on
the fact that environment doesn't change
but the environment it's always changing
around us it may not change drastically
for say a hundred thousand years or so
but it is changing think about this are
climate change right now and how organs
are having to adapt to a warmer climate
or greater levels of toxicity or a
greater influence of disturbance these
are all things that
life forms allowing us and their
populations are having to adapt to
trying to survive in its current climate
so have you looked for evidence of
evolution and we look for a way to show
how this natural selection to drive an
evolution the first we can look at is
what's called homology and homology
bring us back action to the evolutionary
trees where I mentioned the fact that
each one of those little branching areas
brings us to the point where we can see
this similarity from a common ancestor
now the first homology we're going to
look at are homologous structures I'll
send you this basically mean the anatomy
itself so looking at the skeletal
framework in this case is very similar
in terms of a common ancestor but you
might see them used in different ways
for that current specimen so looking at
these four four limbs where you've got
the human for a limb you have the cat
four limb in the way out for them as
well as this bat four wing you're gonna
find that each one of these carry the
exact same skeletal pieces the humerus
the radius the ulna you get the carpals
metacarpals and phalanges but in each
one of these limb forms you have some
that are fused some very more elongate
and shortened so I'm going to even long
gated in thin allowing that skeletal
feature to be basically suited towards
the organism in the fact that we've got
grasping or walking or swimming or
flying but the fact that each one of
these carry this exact same anatomical
resemblance is the fact that we can show
them tracing back to a common ancestor
and more than likely we would trace them
back to one more - like this cat Foreman
but as that cat for them wore this more
terrestrial animal gave rise to the
whale gave rise to a human or gave rise
to a bat we can see this adaptation
where the organism now acceded toward
the environment based on how this scaled
arrangement has changed we can also see
this homology in we call the embryology
and essentially when you look at living
organisms a lot of times you think well
gee they're not going to like them but
when you're looking at all of our
vertebrates so looking at things like
reptiles
birds and fish and mammals you're gonna
find that even though we look very
different out of an adult during the
embryonic development there are actually
a lot of similarities between these two
here we can see the formation of friends
you'll pouches and this formation here
with the postnatal tail now the idea of
embryology is a fact that as we develop
with in our embryonic form some of these
features are lost some of these features
are modified some are left intact in the
case here the post alien tail you would
find that this represents the rear
plumage of that chicken where this is
gonna represent our coccyx on the tail
bone basically termination of our spine
which does not penetrate typically
outside the back of our body but these
are features that we can see in the
embryo that again link us back to a
common ancestor we can also look at
homology and what are called vestigial
structures and for vestigial structures
we see these as since there's a remnant
that in a way it's kind of a lack of use
has left them kind of diminished but
it's more of a fact that as we adapt to
our surroundings or as the populations
adapt to our surroundings that certain
characteristics are favored more than
others
now the appendix here will the scene
with the humans is one as almost always
used as mysterio structure because we
can see that we look back in time our
appendix used to mean much greater in
size with our ancestors and today it's
much smaller and it's thought to not
have been used as much today as it was
in the past now there is more evidence
showing up that the appendix itself
actually still pretty useful and some
are hypothesizing that appendix is
actually used as a source of gut
bacteria that if bacteria are removed
from the gut in some way by antibiotics
or illness or whatever it might be that
the appendix sometimes has a way to
resupply and re flourish with that gut
flora essentially allowing them to
reestablish himself in that system a
better example though vestigial
structures actually comes into line with
our whales and dolphins would classify
elicitation
and that's because in this skeletal
feature you're going to see this remnant
which is the highlight the hind leg of
its ancestor and we'll see you name it
later on in our lectures that as you
look at the transition from a
terrestrial animal to the aquatic world
we can actually show this kind of
feature in the skeletal structure how
we're starting to diminish generations
or regenerations now one thing to
remember especially about all these
structures here whether looking at the
homologous structures or the embryology
or vestigial structures you in
particular these are things that are
changing not over generates my
generation but over hundreds of
thousands if not millions of years that
are slowly changing piece by piece
throughout those generations so with all
the different homologous structures this
can lead us to the formation again going
to back all these hypotheses what are
called evolutionary trees now the thing
to remember especially about these trees
again in fact and these are educated
guesses they're by no means stuck in
terms of their actual pattern but they
are based on what we have seen in terms
of evidence of our DNA evidence of the
anatomy evidence of even just fossilized
remains so a lot of the trees you're
going to see are ones that we can link
back to a common ancestor as a way of
showing relationship now in this very
simplified evolutionary tree we are
actually looking at the evolution of
terrestrial animals so now I can see any
one particular species here as part of
this tree it's more generalizations of
things like amphibians or mammals or
reptiles or birds that's part of that
divergence but to go back to our
original ideas about the evolutionary
trees you're going to sit every single
branching point here is a point of which
we share these things in common for the
part that come after it but there's a
different thing that has changed and
that's left behind for the ones that
come off the side
I'll take for example here looking at
something called the amnion so right
here in between two and three in this
ante on this is actually a
characteristic here we consider as a
homologous characteristic where
everything beyond this point including
our mammals carry us either something
like an amniotic fluid or something like
an amniotic sac or the egg to keep the
embryo in a nice moist environment
you're in Philly Enzo which are
terrestrial do not carry the amnion
they're not gonna have this amniotic sac
or a man like egg to keep their embryos
moist instead the amphibians rely on
water to keep them moist in terms of
live in that environment so every little
point we're looking at every time we ran
a job here you seen similarities or
things that are changing which allow us
to classify or diversify into this realm
here with our terrestrial organisms now
one other thing we can look at here
that's not homologous structures but now
if doctor what are called analogous
structures and the way that these are
different is the fact that analogous
structures carry the same kind of you so
they're the same kind of feature but
they have been met at that point or they
have kind of converged on that point
based on what's called convergent
evolution so you're looking at the left
hand image with a sugar glider which is
our more soupy land the flying squirrel
which is more like us which is potential
you're going to find both these
organisms have these flaps of skin
between the front and the back legs
allowing them to glide from area to area
this technique or this mechanism is not
showing that these two organisms came
from common ancestor that has a flap of
skin instead what you will see is that
for each one of these organisms both
more suitable and placental that need to
occupy a particular niche in this case
your ruling organism that's not flying
but simply gliding from retreated true
tree as a way of finding food it's going
to evolve in both areas kind of along
the same path even though they're not
going to share that common ancestor
over here with these wings the wing
itself is an analogous feature you're
gonna find that it's a similar form in
this case but there is no common
ancestor that had a wing that gave rise
to the insect the pterodactyl the bird
and the bat Lee no yes every single one
of these with these wings at some point
would share a common ancestor going all
the way back to you some kind of
eukaryotic organism but that ordinance
would not necessarily have a wing the
wings themselves are gonna come about
based on the need that this organism is
not flying in the environment or that
this bat is flying that environment so
these are all things but now in
structures up they look like they might
share a common ancestor but indeed they
don't they're all going to get to that
point on independent paths as it means
to have a lucien so when we consider
these homologous trees with police and
loose area trees one thing to keep in
mind is that a lot of this is based on
the fossil record and the fossil records
the only thing we really have to really
give us as evidence to show how things
have kind of come to be and where they
were at some point in time and a lot of
times there's important pieces that are
missing in this case here looking at our
transition from the land to the sea for
what we call the cetacean to the whales
and dolphins there's a piece of the
puzzle that was missing for a long time
that was found to kind of fit and show
how we went from a terrestrial organism
to a kwatak organism and we can see here
with these kind of colorized parts of
the anatomy how the bone structure
starts to be minimized on this case here
goes from a walking leg you're kind of a
back swimming leg to a reduced nub
coming on the back to basically just the
public bone
that's as part of this revenant for this
current form now let's give you an eye
of how complex trees can get in this one
tree we're looking at about 3,000
species or about 1% of the known species
on the planet when you're looking at
this tree you're gonna see that the
edges here we're gonna get you kind of
the modern form and you can notice the
edge is kind of black and color that's
because those branches have gone through
so many branches on that point you can't
see a distinct little line showing up
but you can see kind of the divergence
pattern here we've got all those
homologous structures being similar kin
branching back to common ancestors as we
went all the way back here to the very
middle which would be the common
ancestor for basically all the life
depicted among this image so you can
imagine if we did the other 99% of the
species in this circle probably would be
black for very much most of its
configuration it might have some light
areas here in the middle based on a lack
of the Virgin's the beginning but as you
branch out into things like the bacteria
or the archaea these patterns are little
be much greater than the branching
anything with a protists on the plant so
the animals remailer fungi you'd see a
much greater branching pattern if we
looked at or try to look at every Morgan
those numbers there now as are moving to
Tupper 23 we're still keeping that
evolution on the back of our mind well
we're going to look at a first form of
the evolution what is called the Mike
revolution and even though most
evolution in terms of where species are
being produced is not visible in a
person's lifetime we can see the
progression with micro evolution because
micro evolution is basically in
generation by generation change where
we're looking at the frequency of the
alleles it's good thinking about
anything we can dominant allele or
recessive allele we can see how that can
change generation by generation just do
the fact that there's random mating the
fact that when you make Mason your
gametes
you're going to change the frequency in
the next generation will that offspring
just based on what is passed on from
parent to the offering for that time now
there are four mechanisms we're going to
focus on to kind of show how mic
revolution is happening and we first
look back to natural selection we're
going to see that this is a possibility
where we reduce
variation in such a way that we're
getting favoring organisms we're also
looking at genetic drift with a
reduction of variation when it's
actually a random reduction we get gene
flow which is going to stabilise
variation and we've got mutation which
again is going to introduce a variation
now out of these four mechanisms natural
selection is the only adaptive form it's
the only one that's driven by the fact
the organs was trying to be match the
environment and the other three you're
gonna see that this is not matter
whether or not the organism is sooner or
not sooner the environment these are
changes in variation that have no
relevance in terms of the adaptive form
we think about what evolution now one
thing that kind of pinpoint here before
we get back into natural selection and
looking at some of those ideas is the
fact that when variation we always talk
about the fact that we inherit
generation by generation sometimes
though the genetic variation that we
inherit can be manipulated and it can be
manipulated by certain environmental
influences and our little example at the
bottom here there are two caterpillars
caterpillar and Caterpillar B look very
different when these two caterpillars
though are late as an egg their genetics
are pretty much identical in fact even
when they hatch out learning the
identical forms the change is gonna take
place is the fact of based on where they
are laid on that plant if they're laid
closer to these little flower structures
they pick on this camouflage that more
mimics that flower configuration if
they're laid along one of the stems they
actually pick up more of a stem
configuration so in this scenario these
different variations are picking up all
right consider non heritable because
they're based on the environment they're
not based on the set of genetics that
the organism self contained so evolution
cannot favor one of these over the other
because evolution and natural selection
can only act on variation that has is
heritable or this genetic component if
we passed on generation by generation
now we also will see that
as you look at populations which we're
evolving that geography can actually
play a role in variation and that's
because when you look at most set of
species you're gonna get different
variations due to where they are living
due to the actual geographic range so in
this case here we've got these
populations of mice on this island and
you're gonna find that the mice themself
made a factor the exact same species but
the gene pools are drastically different
the ones on the right-hand side of the
island or the one on the left-hand side
of the island might be exactly the same
in terms of appearance but they're gonna
carry a whole different set of genetics
due to the fact that maybe the middle
the island has a mountain range that
keeps these two populations isolated the
idea is here though the fact that this
variation among these two populations is
actually not due to natural selection
it's do we call a genetic drift and
genetic if simply just a random change
that as these mice originally inhabited
the island as they come to live on the
left or the right hand side of the
island they're now their gene pools do
start to trend apart now the thing about
Geographic variation is that over time
if enough time has passed or elapsed
between these two populations you indeed
can affect we can in fact expect to see
possibly two species being produced or
they're now different from enough from
each other that they can't reproduce
back together in terms of a made an
event for it so since we are looking at
B of evolution by our process with the
populations it's also important to
define what a population is a lot of
times this kind of bias how you look at
certain ideas especially at the micro
evolution level now typical populations
we would say that this is a localized
group where they're capable of
interbreeding and producing a viable or
fertile offspring the key part of this
is localized you could say localized as
bien are the individuals in this class
it could be the individuals at the
college you could be localized for the
people in the state of Florida localized
for
you know people in the United States
that localization is kind of limiting
factor or the kind of bias factor that
can kind of lead you on a path of
different ways of examining a population
but the idea buying this actual idea of
the population is looking at the gene
pool especially in terms of
microevolution because you're gonna see
that in that gene pool every time
somebody reproduces the frequency of
those alleles are going to change now as
time goes by we will find that certainly
l--'s
certain versions of a characteristic may
in fact become fixed where every single
individual in that population is
homozygous for that allele Missa D of
fixing alleles is actually what we
talked about back with Mendel in his
garden piece where he was producing
those two populations but we called the
trubin individuals where they were all
purple flowers or they're all white
flowers in those two different
populations you know the exact same
species you're gonna find one set of
genetics was homozygous for dominant
color and one set was homozygous for the
recessive color so to give the kind of
idea of how we define populations based
kind of on geography if you're looking
at both the birds and the fish because
birds can fly and the fish can swim even
though these two organisms might spend a
lot of time on those Jewish bunch of
habitats you're gonna find there's a
chance that they could intermingle in
some way as the bird flies for resources
or the fish swim around a fine
habitat or whoever might be those paths
may cross which means over time there
could be gene flow between these two
areas where the birds are in the two
areas when the fish are the squirrels
though we would say are different
populations because based on the
localized area that squirrel is not
likely to swim across will walk to the
island or back across the island to the
mainland it's not gonna fly across there
it's not going to go a few mil to reach
between these two populations so over
time those that we saw with the mice
these two squirrels which may be the
exact same species could experience this
Geographic variation you can see here
that we get a more dark gray squirrel
worse maybe more Brown
initially this is just due to the fact
of genetic drift and things like the
gene flow or lack of gene Club which
with these populations again if enough
time passes these two different
populations could become different
species based on the lack of gene flow
and enough differences being accumulated
generation after generation
now we also find in some cases that
population don't have to be isolated
each other we consider two populations
in this example these two reindeer herds
actually occupy an overlapping range now
even though we say that they do occupy
the same range it's not saying that at
that point in time when we see the green
or we see the pink here that those
organisms are actually intermingling
more than like that what we're seeing is
that as this porcupine herd migrate
north you see the four tomorrow migrate
north as well and as in migrate south or
migrate south so even though the ranges
do overlap there's a pretty good chance
just based on migration patterns even
potentially are on reproductive times
that these two populations are going to
stay distinct in terms of certain gene
pools and certain chromosomes
arrangements but more than like because
they do akbar' that same area there's a
very limited chance or less likely
chance that you're gonna see kind of two
species being produced due to the fact
we could still get gene flow we can have
one organism leave the 40-mile herd and
join the poor combine hurt or vice versa
they're now wondering thing we can look
at before we get back into five
mechanisms or that's one of four
mechanisms of our micro evolution is
actually idea called the hardy-weinberg
equilibrium now in your textbook if you
go back and look at this there's a whole
section that goes into use of an
equation where you're using p values and
Q values and trying to establish what a
population looks like if it's not
evolving and essentially what the harder
one would go through looks for is to say
that if these five conditions are met
that this will mean a population is not
evolving which means there's no change
now we look at the five conditions here
you're going to see right off the bat
that number one is something that we
cannot control
saying there are no mutations that's an
impossible feat because notations
themselves even as much as we limit our
exposure to certain mutagens these are
spontaneous there's no way to control
mutations so right off the bat even
though we think about how one word of
showing the populations do not evolve
based on this criteria you're gonna find
that no population or very seldom any
population can actually meet all five
conditions and number one being the
biggest ones they can't meet so looking
at things like random mating or natural
selection not being there or a large
population size or nor gene flow these
are things that we can try to achieve to
some degree but even with a random
mating because we're organism live
because of certain bounds that they can
do in terms of flight or swimming or or
walking you will find that it's maybe
not a true random mating principle
something rolling dice and saying okay
these numbers match up this is where
you're intimated with and even with
human populations you do find that it's
slightly more random now where their
ability to fly across the globe order
take a boat across the globe or drive
great distances but even then we're
still made and using butyl our geography
we're mating within the kind of confines
and normally where we and have it
throughout our lifetime then D have also
known as a selection means that there is
no adaptation to the environment that
the organisms themselves are not favored
any certain way and that's um that's not
subtler than that either possibility now
the lack of gene fo we can do that we
can isolate populations we can say yeah
there's two populations here there's no
gene flow between that is achievable but
very seldom you find that something that
them take place especially if we've got
overlapping ranges and the last one the
large population this is one that again
is kind of biased in this scenario
because what defines large is it a
thousand is a 10,000 and a million what
is it in a large population science
based on those organisms so going back
to our mechanisms then we know that
natural selection is kind of this one
principle that's going to be based on
favoring traits for adaptation
everything else with genetic drift and
gene flow mutation are all random these
are things that really aren't
controlling the adaptation principle
they're more just a way to change
variation within those populations so I
just thought back with natural selection
this is based on the success of the
individual that if you have the better
set of characteristics that are favoring
you in the Africa environment you should
have this grade of success in
reproduction which means that as you
reproduce over time you're influencing
more than the next generation due to
your alleles or to your genetics being
passed on to those next individuals now
genetic drift
Lag natural selection is going to reduce
variation so you're gonna see in a
population if now if you're selecting
occurring over time it's favoring one
condition over another the engine and I
drift the same idea can be at play
except this is a random process it
doesn't matter whether or not that trait
is an advantageous trait or not over
time genetic drift is gonna have an
effect that things randomly change you
might have organisms that fall off a
cliff you might have insects get run
over by a car you might have a set of
cows that get struck by lightning this
is a random process that's going to
change that gene pool and a very short
period of time but there's no influence
in terms of that adaptation principle so
it's still good reduced to genetic
variation the population but it's
because when we lose it alleles usually
due to some kind of death or migration
of organisms that's a random change for
now this idea where this random change
in variation of genetic drift is
actually most profound in a small
population because the smaller the
population the smaller the gene pool and
the greater the effect would be if we
lost same set of harbors of the
population or only 10% maybe moved away
that's gonna rassle change what that
gene pool represents
so the key with genetic drift versus
natural selection is remember that
genetic drift is not influenced based on
the reproductive success that the
characteristic that those organisms
carry have no influence as to whether or
not they're being killed or not killed
during genetic drift idea so looking at
in this population of flowers and this
is kind of a idea about the random
mating that's coming from genetic drift
get out of this population of ten
individuals you had five randomly mate
in the first generation you're gonna
find that out of those five plants as
they leave to the next generation you're
gonna see a change in the frequency of
some of those alleles so we can see at
the bottom down here your pee frequency
is the frequency I would consider the
red allele or the few frequencies the
frequency of the white allele now in
this case this is actually an example in
complete dominance we talked to our back
with our genetics you can see initially
it was 70% of the red allele during the
recent of the white allele when you get
generation 2 due to that random mating
now who made of that generation who
didn't we actually get to 50 50 percent
in terms of its brief in 6 but if the
next generation just these two red
flowers happened to mate and that's the
only allele in being passed on you can
see this fixation at every single
individual now carries as homozygous
condition which show is that red
characteristic or that one red trait on
that flower characteristic if you have a
loss of allele now you can see here
because we only had 10 individuals that
a random effect that whoever happened to
Randy mate or was chosen by the insects
in that time have led to a really
drastic change in the population it's
the loss of one of those alleles so an
it's one here you're seeing a reduction
in genetic variation that's the whole
thing would you then I tripped
now as part of genetic drift there are
two ways this kind of reduction can
happen the first one is headed by choice
a little bit this is the founder effect
and this is where a subset of the
population chooses to maybe move away or
migrate away and occupy some new area or
even if you had maybe your mountain
range formed between or a river formed
between two populations you're gonna
find that a subset has moved away and it
generates its own frequency with those
alleles so the same way that our flowers
in the previous example have this kind
of change and we serve the micro
evolution scale say anything is changing
here with founder effect from the
original population if we assign numbers
that maybe the green trait or the green
with the five fingers would say 95
percent and the sixty Rose was five
percent in that smaller subset that
moves away you maybe now have 75 25 in
terms your ratio and that's just you
have to how the organism cell moved away
to form their own little population so
it's a localised group that are capable
of interbreeding but that's changed that
frequency just not a short period of
time in a banach effect you're gonna
find that now it's not so much the
choice but more the effect that the
environment changes suddenly so a
landslide volcanic eruption looking at
maybe a tsunami or hurricane coming
through you're gonna find that in this
scenario the smaller population is the
greater the effect in terms of that loss
of that gene pool so in our little very
basic example if this bottle with all
the colored bottles and it was a gene
pool and you randomly shake out it's a
small subset you can see that in our
surviving population here there's none
of those yellow little balls it's mostly
blue with only one white that we're
surviving population is nowhere near the
frequency of what it was in a large
population and now I've experienced that
genetic drift of reduction in a
variation
so again like I said before and the
smaller the population the greater the
fact we can see of an attack direct so
in these two little graphs your top one
has a set of 20 unlinked alleles the
population of 10 individuals in the
bottom one you could say here there are
200 unlinked alleles in a population of
100 you will notice here that as you
look at these up and down movements with
our lines in terms of simulations that
in that small population of 10
individuals
there's fixation of an allele or loss
and only very quickly slow hours or us 5
generations in your much greater
population you're gonna see in a case
none about 40 to 45 generations before
we actually start to fix or lose some
alleles in that population that's
because as you get larger and larger
populations that can experience some
up-and-down movement you can go way up
and far way back down but it's kind of
minimized based on the fact and Laurie
bridges are there the grander way we can
actually go with you and had its ups and
downs but still kind of make it run
along the middle in terms of how that
populations going to change what that
gene pool now the other idea of our gene
flow is getting one that can reduce
variation but it's actually due to
variation of between populations not in
a single population by itself and that's
because when you have two populations
that are isolated from each other maybe
by some kind of geography if there is
still a gene flow among those two
populations the ideas of natural
selection and genetic drift are going to
take the pole and they're gonna cause
these two populations gene pools to kind
of migrate apart they're become
different over time but if individuals
are migrating back and forth between the
two populations this random movement
back and forth he is going to over time
stabilize those two populations wind or
gene pool the point that there's no
variation among those two populations so
just like you know nature and just like
natural selection we see a reduction in
variation here in terms of the genetics
but now it's the variation between
populations not the variation within
population now remember the other thing
we can think about here is mutations and
mutations themselves the ones who think
about as producing this new potential so
we're genetic drift and natural
selection and the gene flow are working
on what is there
mutation is only a way to add in a new
variant so when evolution is going to
the process of natural selection and
they're favoring sub conditions over
other ones it's these new variations
that arrived in mutation are the ones
that I can lead us on the path to
produce this better adaptive evolution
for those populations but natural
selection there's one day we're all
going to come back you to show that this
is what's gonna help the Hornets adapt
to its surroundings so when you look at
natural selection
there actually are three conditions that
have to be met in order for this process
to drive evolution and these are all
things you kind of talked about or
alluded to so far the chapters the first
thing is the fact that you've got to
have variation if there's no variation
for that trait so if what would become
fixed in the homozygous condition for
that allele
natural selection cannot act on because
there's no way to show that one part is
more favorable than the other the other
idea is that with that variation it's
got to be heritable which means you have
to be able to pass it on generation by
generation the third car does that
widows individual population you have to
find that one of those conditions is
more favorable or give the orbitals a
better advantage over other conditions
so a rabbit's over here you've got
variation and speed in that variation is
heritable and you're gonna find that the
fastest one or the ones or two survived
loner and we produce four and we should
see a shift in to the speed little
organism a population again we might
oh gee we're gonna create the best
rabbit and the Fox or the the Predators
never going to eat it but in evolution
driven by natural selection you're gonna
find that as a pry them isn't evolving
so is that creditor so even though the
rabbits have different speeds you would
also find that that creditor potential
at speeds that well so you want a fast
medium and slow and that faster
predation might be the one that it's
surviving better which is keep it in
track right behind that faster prey have
you evolved scroll time there's gonna be
a constant struggle for all organisms
the evolved some trait that gives them
better advantage for a period of time
but then so does that predator summon
something now it's trying to compete
with them or to hug them in terms of
this evolution and its natural selection
now in that example we did show that the
best one was the fastest one but in
terms of evolution of natural selection
the idea of the survival of the fittest
does not always correspond to being the
strongest or the biggest or the fastest
in fact with evolution this survival of
the fittest actually comes down to what
is called the relative fitness and
that's where in that population if an
individual can survive longer and
reproduce more they're gonna have a
better relative fitness because they're
making a greater contribution to that
population now natural selection itself
is gonna go through in favor in this
kind of condition because this is where
more genetics are being passed along
generation by generation so even back to
a rabbit scenario if that slower rabbit
maybe was getting more predators you
might find that even though it may be by
some predators if that slowness gives it
a better chance maybe producing a more
viable offspring or maybe have some
camouflage along with it to help it
survive better you might find that
natural selection over time might able
to slow rabbit even though that faster
one could avoid predation
maybe that speed of the faster one is
actually reducing its ability to have a
better offspring you might finally have
actually low and relative fitness so
being the strongest being the fastest
being the biggest and it's not always
going to be the direction of knock
selection domes it can be all based on
which trait or which version is going to
make that population better suited to
leave individuals for the next
generation
now with our natural selection you are
going to find our three main modes of
how those traits are favored in the case
the rabbits we were looking at what was
considered the directional selection
favoring one condition over the other
you also might find that if both the
Fast and Slow were favored based on
other characteristics you might get what
is called a stroke of selection where
the two extremes are being favored or
you might find that if the slow one just
keeps gettin eaten and the fast one is
using too much identity to avoid
predation you might actually find
stabilizing selection where the one in
the middle is now a favor and those
extremes are not favored in terms
evolution these are all ways in which
the actual gene pool can shift due to
the influence of natural selection and
how it's going to increase that chance
of survival and reproduction in the
population again the whole keel
evolution is adaptation it's trying to
match the ordinance to the environment
that kind of adaptation and all you in
the continuous process because the
environment is always changing which
means you're happy new variations coming
about in some kind of form now again
we're not saying every generation we're
saying that I don't think about
evolution long term in the many hundreds
of thousand millions of years that this
is where those changes come to be and
that's how that process becomes
continuous in terms of always trying to
match those around me alright last
chapter for the evolution we're going to
look at now the idea of what's called
the macro evolution so not just the
change of the allele frequency
generation by generation but now much
grander scale
earlier the broad pattern that shows
that as those gene pools start to
fluctuate and as I start to the verge
apart we can now leech the event we call
speciation where new species are being
generated based on how they have adapted
their surroundings
now as we look at this speciation first
thing we have to consider is what
exactly as a species how do we define
this kind of formation and when you look
at species ideas one of the first things
that usually comes into thought is
actually the appearance in fact when you
look at any kind of what's called the
economists key or any kind of taxonomy
that's trying to classify organisms
they're looking for certain morphologies
or physiologies as a way of
differentiating so pick up any kind of
say bird book and you're gonna look and
see inside it says this species is black
or this species is brown this one has a
red crest this one has a certain song
when this one is 20 centimeters verses
will be in ten centimeters there's a
certain kind of her appearance are
trying to describe to emphasize that
species but when we actually look at a
species definition you're gonna find
there are multiple ways of defining what
species are the one that is used most
widely especially in one living
specimens and ones that produced by
sexual reproduction and what's called
the biological species concept with this
idea we're gonna see that a species
itself was identified based on being
part of a group or part of a population
where those members can potentially
interbreed so basically made together
and whether interbreeding we're looking
at a natural setting so we say
interbreed in nature and that
interbreeding produces not only a viable
but a fertile offspring now this also
means that they're not going to breed
successfully with other populations so
this mean that if you had a population
of say Appliance and a population of
hyenas cuter bird species it might be
overlapping that might be part of this
natural setting but they're not going to
breed I'm not going to go through
successfully change or exchange gametes
maybe a better unit will be corals in
the ocean you know they're all intra
mingling together in that same
environment but you're gonna find that
they're not going to go through and we
call hybrid I
into a whole new species now this idea
about keeping these populations distinct
and goes back to our definition of
populations we're talking about the gene
flow if we can have gene flow between
populations that's gonna keep that kind
of gene pool more stable keep that
population linked together as soon as
gene flow stops though this is where we
start to leave the point of producing
this chance where we don't produce a
viable and fertile offspring yet the two
populations come back together so we
look at this kind of violent species
concept we're emphasizing the idea about
what's called reproductive isolation the
fact that there are certain factors out
there to keep two species or two
populations from producing that viable
and fertile offspring now back with
Mendelian genetics we do bring an idea
about hybridization and where Mendel
took the two parents and produce the f1
so we would call the hybrids we said the
fact that those are not true hybrids
because hybrids himself usually coming
for the crossing of different species
but in Meadows case we were treating the
True Grit population in the purple
flower and the true red population of
white flowers kind of distinct
populations and show that they could
interbreed and produce a viable
offspring so even though hybrid wasn't
the best term there we do see kind of
the mixing on the conditions and that's
what you seen with actual hybridization
with different species they're gonna mix
together their different characteristics
into some new organism now in terms of
this isolation for reproduction we're
going to see two types of barriers the
prezygotic barriers and post I got egg
once increasing Adak barriers we're
gonna look at this as the events before
the zygote is form
Anthony pre-zygotic and the first thing
we're gonna look at here with habitat
the temporal isolation and behavioral
isolation these are all things that
basically keep species apart it prevents
the median attempt so occupying
different habitats so terrestrial versus
aquatic occupy different times a day so
be in something that's active at night
versus the day
we even that one it is active
reproductively in the spring versus the
fall these are in keep populations
isolated even a behavior like a certain
courtship ritual it's enough to keep to
speciation mating together especially
with bird populations now beyond the
actual mating attempt so if we overcome
those first three barriers we can get
mechanical isolation so essentially the
wardens don't match up quarry to allow
the main event but if we do overcome a
chemical isolation we also have comedic
isolation and this is particularly
important when you look at things like
our who should go in organisms where
maybe they're broadcasting their gametes
so at coral or maybe another
invertebrate sort of sailing game it's
in the longer column we've got to have
the right kind of signature for gametes
to be it up now if we overcome all those
first barriers we give it the pointer
for analyzation and we make the zygote
so the rest of our reproductive
isolation we can see what are called
post psychotic barriers and easy barring
that happened after that as I go to
school so first we're gonna get is a
reduction in the hybrids viability since
you means that if we make that zygote as
I go it's not gonna live long in terms
of embryonic development it's gonna be
aborted early on or if it does come out
as an organism it's not gonna be four
correctly it's not going to survive as
an adult form we can also have the fact
even if we do survive through the
embryonic development and would survive
to a functional individual you might
have a reduced fertility or reduced
ability to send on our gametes and
that's particularly the case here were
you looking at something like the mating
of a donkey and a horse to make a mule
the mule Sherry's sheriff's kick common
characteristics among these two
organisms but you're gonna find that the
mule can't reproduce on its own it
doesn't have them known to send on
gametes those gametes are not formed
correctly
the last of them comes down to what's
called hybrid breakdown so in a hybrid
breakdown you're gonna find that the
hybrid itself essentially is viable but
because it's a unique kind it may not
have anybody else to reproduce with it
may not be able to go off and same
gametes the next generation or even if
it is from like a plant that can self
fertilize or basically Quillen it so
you're gonna find you're limited in
terms of how they can actually send in
an exon generation by generation as you
move down the line now again the biota
species concept focuses on the fact that
organism is sexually producing and as a
lie so you're looking at prokaryotes
which asexually reproduce or looking at
fossils which are dead this concept
really does not allow us to examine how
species can be defined go to finding
bacteria based on this doesn't work the
finding may be a piece of a bone
fragment or see dinosaurs based on
fossilized records doesn't really work
as well in terms of the concept trying
to show the lack of gene flow between
populations show that lack of
hybridization
so beyond the bowels of species concept
we giving other ideas like the
morphological species concept looking at
the actual structural features we look
at ecological species concept looking at
what kind of niche or what kind of party
environment very happening or even the
phylogenetic species concept we're
looking at the fact that we can put them
into the degrees of difference based on
those evolutionary trees trying to show
that relationship among those I those
forms
now one of the last things for us to
consider here is the fact that if we do
overcome all these barriers and let's
say we've got a population that is
essentially going to produce a new
species at some point in time there
actually are two different modes of this
macro evolution or this speciation and
it comes down to what is called the
allopatric speciation which we often
time to call the other country
speciation and we have the sympatric
speciation what sometimes we call the
same country speciation so we can see on
the side here the trees and the first
example being divided by some kind of
barrier allopatric speciation in our
country speciation versus sympatric
speciation you have a new species
development right amongst the original
population so get into both versions
here you're gonna find that in these two
modes you might have two very different
things happening in the allopatric
speciation usually involve some kind of
geographic barrier so the first one the
trees you had a river run through it in
the case with our little fish population
you had a water level drop the idea here
is that we're limiting gene flow that's
the biggest mode it allow us to reach
allopatric speciation in sympatric
speciation though you're not going to
have a change in geography instead
you're using the former new species
based on some kind of other selective
pressure whether it's mate selection
maybe it's a change in chromosome number
new T mutation these are things are
going to take place from the in the
actual population or the could be gene
flow is still among all the individuals
so an aliphatic speciation were the
other country speciation you're gonna
find that the gene flow between the
populations which would normally reduce
that variation is not interrupted we're
gonna barrier like a mountain range or a
barrier like a river or even a barrier
as simple as a road I know how biggest
the species are could be enough to
produce this kind of isolation
even go along the lines of genetic drift
and natural selection even mate
selection with sexual selection are
things that any isolated populations can
drive those to gene pools further in
front of the park now one thing that is
considered here in the aqua tech
speciation is actually what the species
is capable or not capable of doing so a
berry here all depends on the organism
in our little populations here these two
ground squirrels a giant Canyon is a
barrier but if we're looking at a
population of birds or maybe coyotes or
even something like a plant with pollen
grains that Canyon may not be enough to
keep the populations isolated and you
have a less of a chance to show the
effect of speciation when sympatric
speciation though you're gonna find out
that these are organisms the overlap and
the same geography and usually you're
going to find that some kind of
reproductive barrier he is gonna isolate
those organisms so in this case here it
could be a change in time of day they
want to mate
maybe for some reason they favor the
morning where the other part of
population favors evening maybe even
time of year maybe there's been a delay
in reproductive form by a matter of a
week or two weeks this could be enough
to keep those individuals separate and
produce that speciation so going back to
some of our ideas we talked about for
polyploidy especially in plants we
talked about the extra chromosome set or
double in that set their natural
selection also in favor of this if you
have a certain trait that the other
medium doesn't favorite doesn't like
especially terms of sexual selection you
might find that you're not favorite or
chose him and that leads to a lack of
gene flow and this isolation takes place
for
so when you think about this idea of
speciation get at this kind of grandiose
scale of macro-evolution
you are going to find that this kind of
course of speciation is all a very broad
pattern and we will use this and say no
this is a speciation event here or there
but this takes place over several
hundred thousand if not millions of
years in fact the shortest amount of
time we've estimated for speciation
he's as long as four thousand years and
some of our fish species upwards the
automated 40 million years in some
insects and he would about the average
about 6.5 million years that's a long
time interpret species being produced
for us but the actual patterns here in
terms pc asian are still kind of left to
debate is evolution base of a punctuated
pattern where we have one species
changing or diverging due to some
drastic change and then going through we
consider what's called a stasis or a
stability and time or do you find a
graduated pattern where over time those
individual characteristics are slowly
accumulated a bunch producing these two
species and either one of these patterns
are the hardest thing to identify is
when in fact let's say the punctuated
pattern these two actually classify as
an distinct species keep in mind that
with our dogs having a chihuahua versus
a great day they look very different
characteristics for the same species
so having two butterflies as in this
example here look very different does
not guarantee that they are in fact
different species but it does show the
track that over time may be due to
selective pressures may become two
distinct species new to a lack of gene
flow even down here the gradual pattern
I just showing these slow accumulations
where does one species start and one
species stop in terms of that trend the
ideas though is the fact that what
evolution and that's kind of both
patterns we go with you a great period
of time that you might have a gradual
pattern and then all of a sudden you're
stuck with that same organism or that
same condition for a long
period of time and then maybe something
changes the environment you get another
gradual change or even a drastic change
and you go through these patterns of
change throughout time leanness down
this path of our evolution
remember evolution he's on the
population level and this is a simple
modification your natural selection in
the individual is the one that's going
to favor that condition which best suits
the individual or makes them best
adapted for that environment so that
concludes our evolution chapters and it
also includes our last bit material for
the semester okay don't forget if you
miss some slides along the way here or
you want to go back and revisit some of
the information look back on to the
website and pour the slides on the road
or see something information might've
missed
