hey biology students in this new lecture
series we are discussing the theory of
evolution now in this cartoon we have
the guy here saying don't call it
evolution the little guy in back gets
offended while I start with this cartoon
every semester because I realized for
many non scientists the theory of
evolution is controversial and maybe
even offensive and I like to be really
clear and upfront that my goal is
obviously not to be offensive to you
regardless of your religious viewpoints
so over the years students have asked me
some students have asked me why don't
you talk about creationism or the
judeo-christian viewpoint the reason is
that this is a class a college level
class on biology I have utmost respect
for the world religions however I am NOT
an expert on world religions and this is
not a class on world religions and so my
expertise is in science and that is the
perspective you are going to hear in
these lectures and as we move forward
with the remainder of the semester we
will be discussing the theory of
evolution from the scientific
perspective please note this does not
have to be your perspective at the end
of the day what you believe or not
believe is your choice and so please
don't feel like you have to abandon your
religious viewpoints in order to
understand the concepts that we will be
describing in this new lecture lecture
series and I do also like to let you
know that many scientists still believe
in God and have religious viewpoints
that are that actually can blend with
the theory of evolution in many world
religious leaders have made that very
clear to their followers for example the
Pope has made it very clear to
Catholics that theory of evolution and
Catholic teaching is compatible belief
system so you don't have to reject it
but you certainly don't have to feel
like I'm pushing you towards towards
what you don't want to believe or not
believe for the purpose of this class
though I do expect that you understand
the principles of the theory of
evolution and that you're able to to be
tested on that and understand that okay
so with that out of the way let's get
started
so a lot of people don't understand what
we mean by the term evolution and really
the term evolution really means change
it's really change over time so I'd like
to start with an example of something
that we have seen evolve over our
lifetimes and that is the evolution of
the cellphone so although probably most
of you grew up with cell phones back in
the old days probably early early 90s
this was the original cell phone it was
huge and bulky and you know this would
not be something you would fit in your
pocket but the next version of that the
next change the evolution of the next
cell phone was something similar to this
the little Nokia phones now this was
around the this is when I remember cell
phones starting to become popular and I
remember I got a Nokia phone and texting
was just becoming a thing and I couldn't
figure out why anybody would text
because this was back when you had to
push all the buttons it you know one at
a time over and over until you got to
the letter that you wanted and you kept
having to do that it would take forever
to text and I would just thought to
myself why is anybody texting I don't
understand why anyone would do that then
there was the flip phone remember that
you might even know some people that
still have flip phones I know my
grandparents finally just gave up their
flip phones but there was the flip phone
model and then of course our beloved
smart phones or iPhones that really
revolutionized cell phone technology so
this concept of evolution just means a
change okay a change in form that has
occurred over many generations so here
we're seeing generations of Technology
generations of cell phones let's apply
that principle to how it
relates to biological systems so we use
this term biological evolution and
here's how I would like us to define it
for the purposes of our class so I'd
like to define it as a change in the
inherited characteristics of a
population over time that is the
definition of biological evolution so
notice it also refers to a change just
like we talked about the change in the
different cellphone models over the last
30 years or so very important though the
term inherited so these inherited
characteristics what do we mean by that
well we mean that this is this these are
traits that are encoded in the DNA of
the organism so in order for biological
evolution to work this has to be at the
gene level the DNA level okay so it
can't be characteristics that we acquire
during our life so we can pass on the
instruction book written in our gamete
cells but if you decide to dye your hair
blue that is an acquired characteristic
and obviously that wouldn't pass on to
your offspring now that seems sort of
obvious but we will look at some
scientists in the early days of trying
to understand how evolution worked and
they actually made that error in their
thinking they didn't realize that it had
to be encoded in the in the DNA it had
to be inherited the other important part
of this definition is that we're dealing
with populations so when we discuss the
evolutionary process this is something
that occurs in populations we look at
the frequency or the
centage of certain characteristics
within a population we don't look at
that in terms of individuals so in just
single generations where individuals
show changes to their phenotypes that
would not qualify as the definition of
biological evolution we need to see
broad sweeping changes in many
individuals within a population rather
than single individuals and then the
other important part of this is the
overtime part the point being that
evolution doesn't happen in a single
generation even in mini or a few
generations it's many many generations
now for some single-celled organisms
like bacteria that can be a relatively
short amount of time and the reason is
that bacteria reproduce in some cases
every 20 minutes so their generation
time is very short and so it's possible
to see the biological evolution of
microorganisms in a short amount of time
but for large organisms especially
animals and especially in humans this is
going to take many generations thousands
of years sometimes millions of years
before we're able to see these changes
take effect within a full population
okay let's talk historically about
evolution now you may know the founder
of modern evolutionary theory is Charles
Darwin but he actually wasn't the first
person to realize that organisms could
change over time but he was the first
person that got it right in terms of how
evolution works so first let's talk
about how evolution does not work so
this scientist that jean-baptiste
Lamarck lived in the early 1800s in
he was on the right track in terms of he
understood that there could be changes
in populations that could accumulate
over time but his mechanism was flawed
so he for example he thought that the
giraffe got its long neck from the use
or the need for that that neck to be
long in other words in order to reach
the tall leaves on the on the top of
trees to reach that food source he
thought over time they must have just
stretched their neck in order to reach
the tall trees and this is actually
obviously not how it works so this is
false so it is possible of course in
science for false information to
initially be described and then later
discredited and that is definitely the
case with Lamarckian understanding of
evolution this is not how it works
so in fact Charles Darwin had read some
of Lamarck's works and he called his
work absolute rubbish meaning that this
is obviously not what happens we can't
make ourselves change our phenotypes we
can't stretch our arms or stretch our
legs or stretch our necks in response to
environmental conditions that's not how
it works and in fact he called his he
called it he called it the theory of
acquired characteristics that we would
acquire characteristics during our
lifetime like stretching your neck and
that that would be inherited
and obviously that's not how it works so
along comes Charles Darwin I want to
tell you about his story here what's
significant about Charles Darwin is that
he's the first person to publish a book
on the theory of evolution with a
mechanism of how evolution happens that
he called natural selection he actually
wasn't the first person to even come up
with the concept of natural selection
and somebody almost beat him to the
prize of updating recognition for that
and that was the scientist Alfred Russel
Wallace who actually wrote to Charles
Darwin and had come up with the same
idea and Charles Darwin said oh shoot I
better publish this you know so they
they they publish that joint essay but
then Charles Darwin published his very
famous book on the origin of species
published in 1859 now here's a picture
of Charles Darwin in his older age
looking a little bit like Santa Claus
okay but I'd rather talk to you about
Charles Darwin in his younger days so
here's a picture of Charles Darwin in
his early 20s Charles Darwin came from a
very wealthy family in England where his
father was a medical doctor and his
grandfather was a medical doctor and it
was understood that Charles Darwin would
follow in the family footsteps and he
would also become a medical doctor so he
attended medical school in England and
he hated it you have to understand in
the early 1800s this was a very
difficult time to be in medicine because
people didn't understand how infectious
disease worked they didn't understand
microscopic germs
for example surgery was a spectator
sport if you can imagine you could go
and watch surgeries in an arena sort of
like we go for you know watching a
basketball game you could watch in a
stadium surgery and of course there was
no
sterile technique the doctors the
surgeons were using the same bloody gory
utensils on everybody there was no
sterile operating rooms you know like
there is today so infection was rampant
and it was a really terrifying time in
medicine and Charles Darwin wanted
nothing to do with that so he dropped
out of school he moved back in with his
parents to their horror and to their
shame he wasn't following in the family
of what steps and they said well if
you're not going to be a medical doctor
the other respectful thing to be would
to be a priest in the Church of England
be an Anglican priest and Charles Darwin
was actually deeply religious and he
considered that but right around this
time he learned of a job opening and the
job opening by coincidence somebody had
dropped out somebody who is going to
serve the job of naturalist on the HMS
Beagle a ship that would go on a
five-year journey around the world and
this person had dropped out and they
were looking for a naturalist to go on a
five-year journey of them around the
world reflect on that and then I know a
lot of you are in your 20s and without
having you know a spouse or children to
look after think about that if you
somebody said would you like to go on a
five-year journey around the world that
might be actually pretty desirable and
Charles Darwin thought so as well to be
a naturalist meant to take record or
record what he saw on this journey
including taking specimens of animals
and plants and also rocks and things
like that that they would find on this
on this journey so here's where they go
they go from they leave from obviously
from England and they go follow this
path here as they go around the tip of
South America
and you may know if you know anything
about Charles Darwin he really had a
fondness for these collection of island
islands off the coast of Ecuador and
very famous these are called the
Galapagos
so we spent a lot of time there and then
they left the Galapagos and they went up
around Australia around the tip of
Africa and back up to to England and
this was very cool because nobody had
seen these places before and that's a
very rare thing and today isn't it
there's very few places today in the
world that there isn't a huge human
influence where people have been there
already Charles Darwin had this unique
opportunity to go to places around the
world that people had never been before
and to see things that nobody had ever
seen before
if you've ever had the opportunity to
travel just in your lifetime so far
saying go to other countries other parts
of the world maybe some of you are
military and you've you know you've
you've been to the Middle East and
you've seen what that is like
those sorts of experiences they change
you they change your perspective and it
certainly changed Darwin's perspective
because the perspective of the
scientific community at this time was
very much the perspective of the book of
Genesis in the Christian Bible and what
the book of Genesis implied was that
life on the planet had been created in
about seven days by God and that life
hadn't changed at all since that since
that time and it was also proposed that
the earth was relatively young maybe
just a few thousand years old
but what Charles Darwin observed on his
five-year voyage around the world really
got him thinking about that and
realizing that that didn't make sense
with what he was seeing around the world
so he witnessed major geographical
changes major storms and tsunamis and
droughts and floods and all of these
mental changes that would occur in these
places and then noticing that the the
organisms the plants and the animals
that lived there were well adapted or
would change along with the environment
on the Galapagos there's a lot of really
cool animals to understand I
particularly love the tortoises and I
know Charles Darwin did as well one of
the cool thing of things about these
tortoises on the different islands in
along the Galapagos so there's several
different different islands that make up
the Galapagos is that they each each
island has a unique species of tortoise
with unique adaptations in form so
unique phenotypes so take a look at
these two tortoises and you notice that
though tortoise on the right this
tortoise comes from Pinta island and
you'll notice that the tortoise is on
Pinta island they have very long necks
see that look how long that neck is well
that's because there's not a lot of
vegetation on Pinta island and it's a
huge advantage if you have a long neck
and you can reach vegetation that is
higher up off of the ground compare that
to the tortoise on the Left the tortoise
on the Left comes from santa cruz island
one of the Galapagos Islands notice that
they have very short necks that's
because there's a lot of vegetation you
can see how green it is Sara on santa
cruz island so you don't need to have a
super long neck in order to reach
vegetation because low to the ground is
fine and also there's a lot more
predators on santa cruz island and so if
you have a long neck it would be easier
for a predator to grab your neck and
devour you so having a short neck is
what we call an adaptation so it's an
adaptation
to have a short neck on Santa Cruz
Island but the reverse is true on Pinta
island it's a better adaptation to have
a longer neck so the question here is
really how did these neck lengths become
so variable among these tortoise
populations because it wasn't Lamarckian
theory of acquired characteristics
remember he would say well it's because
they must have stretched and that's how
they got that well that's not how it
works
so Charles Darwin returns from his trip
and he returns from his trip in 1836
notice though when he actually publishes
his very famous book On the Origin of
Species he publishes his book in 1859 it
took him 23 years to finally publish
this book why was that well when he
returned from his trip he was still a
young man in his 20s and he realized
that the ideas that he had were
revolutionary and we're going to shake
the world of biology and we're gonna be
highly unpopular almost like a heretic
situation and he was actually afraid he
was afraid to publish his ideas and it
took him 23 years of careful planning
careful writing careful research he
wanted to make sure that he was right
about this before he put himself on the
line and he wanted to be careful about
that because historically if you know
anything about historical science
scientists like if you know Galileo the
story of Galileo the scientists who
proposed that the solar system centered
around the Sun instead of the earth
which we now know is correct but that
was heresy and he was thrown in jail by
the Catholic Church so scientists were
hesitant to refute popular opinion
because of the fear of being punished so
he wanted to make sure he was absolutely
correct about this and the amazing thing
of what he came up with here in his book
is that it has stood the test of time
the test of modern science and he he
recognized this pattern and he describes
it and he calls it natural selection and
everything we know in biology supports
this mechanism now it's not the only
mechanism for how evolution works so in
the next lecture video we will be
discussing other mechanisms for how
evolution can occur in populations but
it certainly is a major mechanism for
how evolution works so let's get to
explaining how that works so Charles
Darwin by the way so he was concerned
about how how the Royal Society of
London this elite group of scientists
would view his book so in the beginning
of his book he actually describes a
concept that everybody understood
because everybody had been doing this
for thousands of years and it's called
selective breeding now we've talked
about this we talked about it in the GMO
lecture because I make the connection
that what we've been doing in farming
for thousands of years is really the
same thing that we're doing now in a
more targeted approach in GMO organisms
but the concept is that farming is
really not natural it involves the
breeder or the farmer taking animals
with particular traits and breeding
those animals so that their offspring
have those traits we've talked about
this remember the Belgian blue cattle so
how did these cattle get so so big and
beefy well it's because they were bred
where the beefiest the beefiest cattle
were cross bred
and that yielded beefy offspring and
then those were crossbred and after many
generations you get this line of cattle
that overproduce his muscle have large
muscles and look like this
okay how about award-winning horses so
if you have a horse that wins in the
Kentucky Derby you can sell the sperm of
that horse for many thousands of dollars
people will pay because it's understood
that if you have an award-winning horse
that's it particularly fast at rate
racing that that potentially could be
genetic and they want that sperm so they
could breed more horses with that trait
breeds of dogs so all of the different
breeds of dogs that is not natural that
is a result of us of humans we select
for traits coat color appearance length
of the legs and all of these things that
we think are desirable and we crossbreed
these dogs and a lot of that involves
inbreeding by the way breeding brother
and sister dogs to get these desired
phenotypes it's also on a side note one
of the reasons why meat certain breeds
of dogs have some genetic problems is
because in the process of selectively
breeding them for what the breeder
thought was a desirable trait they had
to in breed those dogs and when you in
breed when you breathe brother and
sister that increases the probability of
homozygous recessive mutations showing
up and so we you know a lot of them have
other types of health problems because
of that process now this is not just
unique to livestock and to animals this
is also true in plants we've talked
about this before but that all of these
vegetables you see on the screen here
from broccoli to cabbage to cauliflower
to kale that is also a result of
selective breeding so they all come from
the wild mustard plant and so you know
ten thousand years ago we're breeding
wild mustard
different different varieties of the
mustard plant to give this desirable
outcome and so he starts this book by
helping everybody understand hmm we've
been doing this selective breeding for
thousands of years it's called farming
we also call it artificial selection you
should be familiar with that term
it's called artificial
selection and that's because humans a
breeder or the farmer is acting as the
selecting agent as opposed to what
natural selection involves which is the
environment selecting for a specific
trait so he makes this connection for
people in the book he says we've been
doing this process it you know
artificially for thousands of years
everybody knows if you crossbreed two
animals with the Descent with a
particular trait and their offspring
have that trait and then their offspring
have that trait now we've changed the
characteristics of that population we've
evolved that population but in an
artificial way in a way that we designed
he said well if this can happen in
farming couldn't this happen just on its
own in nature and with environmental
changes could those environmental
changes drive this process
let's take a look at a paragraph from
his famous book on the origin of species
where he describes a natural selection
he says as many more individuals of each
species are born than can possibly
survive and as consequently there is a
frequently recurring struggle for
existence it follows that any being if
it very however slightly in any manner
profitable to itself under the complex
and sometimes varying conditions of life
will have a better chance of surviving
and thus be naturally selected from the
strong principle of inheritance any
selected variety will tend to propagate
its new and modified form
now that's 1859 he is a very eloquent
writer but this is obviously written in
the language of the 1800s so maybe it's
not entirely relatable to you but there
are some key terms that I think are
important to understand he understands
that there are more individuals than can
possibly survive there's something he he
coins the stern struggle for existence
there's there's this competition among
organisms and then some happen to have a
better chance of surviving and thus are
natural naturally selected so we're
going to break this down into the key
points about natural selection so the
first thing to understand and Charles
Darwin understood this as well is that
in every population there is variety
more often in sexually reproducing
organisms than an a sexually reproducing
organisms and that's simply because of
the process of meiosis right that leads
to the scrambling of the DNA in every
generation but look around there's
variety isn't there
everywhere you look here we see
different bunnies with different coat
colors the amazing thing to me
Darwyn of course recognized that
variation had to be present in order for
natural selection to occur but the
amazing thing to me is that he publishes
his book in 1859 now he was actually
contemporaries with Gregor Mendel the
the founder the founding father of the
field of genetics however they never
knew each other knew of each other
because back then of course there was no
social media there wasn't frost
collaboration between scientists in
other parts of the world like there is
today and so he did not know anything of
what gregor mendel was doing he didn't
know Charles Darwin nothing about DNA
DNA what DNA was and how it worked why
that wouldn't be understood for another
100 years after Charles Darwin but the
amazing thing to me is that he figured
this out without knowing anything about
what Mendel was figuring out with with
how heredity works and without knowing
anything about DNA and he was right on
and with modern technology and modern
biology everything is exactly the way he
predicted it so today we now know he
didn't know this but we now know that
mutations occur in the DNA and this
produces new alleles and when we get new
alleles that can lead to variation that
can lead to new traits this is also
genetic variation is also a result of
meiosis if you got anything out of
meiosis hopefully you got the point
across that due to crossing over that
special event in prophase wine where the
homologous pairs they swap segments and
member that's way we make the
chromosomes sort of multi-coloured
looking at that point to sort of model
that they're swapping large segments of
chromosome with their homologous partner
chromosomes and then the shuffling of
the chromosomes that occurs an
independent assortment where there's all
these probabilities possibilities of
which chromosomes will actually be
separated in into the gamete cells so
there's all of this shuffling and
there's the mutation that occurs within
chromosomes
and all of that is very important to the
process of natural selection and occurs
randomly okay
so natural selection is the process that
acts on that variation very simply take
a look at this picture here we're
looking at these two different variants
of caterpillars so they have two
different phenotypes right so we've got
the green caterpillars and we've got the
blue caterpillars and they're both
happily eating their green leaves but
along comes a predator a bird bird comes
along and you can see that the bird is
eating the blue caterpillar why did he
why did the birds select for the blue
caterpillar rather than the green well
it's because the green caterpillar is
better camouflaged isn't it the chemical
flage green capsular blends in with its
environment and is less likely to be
eaten so we use this term selecting
agent or select selection pressure to
describe what can happen in the
environment so remember the natural
selection process refers to what happens
in the environment when there is variety
of phenotype and and depending on the
environment there can be the pressure
that can select for a particular
phenotype so what are some examples of
selecting agents or selection pressures
that we see in nature
well what's described in this make sure
is predation so when there's a predator
that's out to eat you and if you have
some adaptation that allows you to
survive that predator maybe it's just
camouflage like we see here with the
caterpillars now you have an adaptation
so we would we would say that the
phenotype of being green is an
adaptation in this particular
environment and we would
say the selection pressure here would be
predation by the birds okay other types
of selecting agents are selective
pressure things like that can occur in
nature so things like shortages of food
or shelter so again things where certain
certain organisms will survive or you
know if you have that long neck right
you you can reach the food and those
with the short neck they can't and they
die off and you survive and you
reproduce and you pass on that trait
there we go now we have we have a
selection process things like disease
can be a selecting pressure so disease
that wipes out certain groups of
organisms and other organisms that have
a better adapted immune system perhaps
they they survive things like poisons
poisons can be selective pressures
because it can kill off certain groups
of organisms and other organisms with an
adaptation would survive competition
simply other types of competition and
going back to what Charles Darwin
referred to he referred to this process
of natural selection he referred to it
as this struggle for existence he said
there would be a struggle for existence
in nature that there's going to be
competition there's going to be
environmental shortages there's going to
be disease there's going to be predators
and if you have that advantageous trait
you are going to be more likely to
out-compete others in your in the in
particular environment I thought I would
show you a simulation on this process
let's take a look
okay so I found this simulation of the
process of natural selection I wanted to
share with you and here we see this
little white bunny here and the
environment
if says this very brown they actually
call it the Equator environment so in a
warm climate environment now it says add
a friend because he needs a friend here
so now there's two bunnies two white
bunnies and bunnies will do what bunnies
do which is they'll reproduce okay and
they'll start making more white bunnies
because this is a inherited
characteristic to be a white bunny and
this will happen in bunnies really fast
and Charles Darwin noted this that in
every population there's sort of this
overproduction but we're not just
overrun with bunnies our weight right
now it looks like we're overrun with
bunnies well what happens if we
introduce some wolves into our
population well the wolves are going to
start cutting down on this bunny
population but let's go ahead and
introduce a mutation into the population
and the mutation
now codes for brown fur so now the
Wolves are in there and they're still
eating the bunnies but notice that the
Wolves are eating in preference they're
eating though white bunnies compared to
the brown bunnies it's that same story
like with the caterpillars where if you
have got the ability to camouflage in
your environment you're better adapted
so over time what we begin to see is
selection caused by the predation of
Wolf's for the brown bunny compared to
the white bunny and over many
generations we see that white bunny
trait start to disappear in the
population and we we have now more brown
bunnies but notice what happens if we
shift to the arctic okay so change the
environment and now boy those brown
bunnies they really stand out don't they
and the Wolves come in and now who are
the wolves gonna eat well they're gonna
eat the brown bunnies and they're gonna
leave the white bunnies alone because
the white bunnies are better adapted in
this particular environment the white
bunnies are better adapted and so the
Wolves come in and they and they take
down the
buddy population now there's other
adaptation of there's other selection
factors or selecting agents
let's put food in there but some food
food is pretty scarce and now let's
change change mutation will give a long
teeth to some of the bunnies all right
here's a long tooth bunny here and a
long tooth bunny there's brown and then
there's white long tooth bunnies so what
happens is this long tooth bunny is
better adapted for getting the food
compared to the short tooth bunny and
what happens is over time we see more of
the long tooth - bunny than the short
tooth - bunny so now we have a different
type of selective pressure this time
food rather than predators so food
stores can also select for certain
traits to become more common in a
population so two more important
characteristics to add to your
understanding of natural selection so
the first thing to understand is that
this refers to certain genetically
controlled phenotypes that are more
advantageous in a specific environment
so it really depends on the environment
and that individuals with these into
advantageous traits they are more likely
to survive to reproduce and to pass on
those traits we can also look at this
graphically let's go back to the
caterpillar example so there's no
selection we wouldn't really wouldn't
see a big difference in the numbers of
blue caterpillars compared to green
caterpillars but in the right graph what
would we predict here after selection
pressure of predation over many
generations remember that's an important
principles that it's over many
generations several generations we start
to see a change in the inherited
characteristics and remember that's how
we're defining evolution is a change in
the inherited characteristics so several
generations later the blue caterpillars
are in the decline
maybe they even go extinct we're green
caterpillars are increasing or staying
stable in the population and the reason
being would be natural selection this
wouldn't be just random chance okay this
would actually be because the green
coloration is an adaptation in this
particular environment where selection
pressure predation is acting on the
population
so let's summarize natural selection of
what we've learned today so we've
learned that in order for natural
selection to occur there has to be
mutation and mutation actually causes
populations to have phenotypic variation
or what we call genetic variation and as
a result of mutation we end up with new
traits in that population and then if a
particular trait is advantageous over
another then we get natural selection
and if that particular trait becomes
common in the population over many
generations then we say we have
evolution we have a change in the
characteristics of that population I
thought we could apply natural selection
to one more example before we go and
this is related to a topic that I
particularly enjoy learning about myself
because my background is in microbiology
and this is a very important problem in
the medical community right now and the
problem is antibiotic resistance
now I mention this because although like
we said at the beginning of the video
you can decide whether or not you choose
to believe or not believe in certain
concepts in biology and evolution being
one of those I do think there is a
fallacy to saying oh I believe in
evolution or I don't believe in
evolution because evolution to
scientists you see it's not a belief
it's based on evidence evolution is
based on evidence so I wouldn't say
personally I wouldn't say I believe in
evolution I would say I accept the
theory of evolution based on the
evidence and so sometimes I do find it
interesting when people say oh I don't
believe in evolution it doesn't happen
natural selection is not happening and I
say really well would that be nice
because if there was no such thing as
evolution there wouldn't be antibiotic
resistance and this is a huge problem
a huge reality in medicine what this
literally means what this means is that
the medications that we use to treat
bacterial infections are not working on
the bacterial pathogens and the reason
is that the pathogens are evolving let's
take for example tuberculosis so
tuberculosis disease is caused by a
bacterium that's called Mycobacterium
okay so Mycobacterium causes the disease
tuberculosis almost write it as TB TB
disease these are the bacterial cells
you see they look sort of like these
sort of look like tic tacs they're very
small they they get into the lungs and
they cause a major disease in the lungs
where when you look at people who have
tuberculosis on chest x-ray it's just
what a chest x-ray looks like for
somebody wants to Burke you low sis you
see all that white stuff in there that's
not a good thing when you take a chest
x-ray of somebody you should just be
seeing black in the lungs on the x-ray
because there should just be air in
there and your lungs there shouldn't be
pus and all this growth of bacteria this
is what we see in turmeric you OSIS when
we have a patient with this disease and
they are very very sick and they'll be
coughing up blood and all sorts of
things
well since the advent of antibiotics
around World War two a lot of bacterial
infections have been we were able to
cure them using antibiotics but
resistance means that the antibiotics
are no longer effective on the bacterial
populations and why would that be well
it's because of evolution so let's spell
it out for you here the four major
points to understand when it comes to
natural selection these are the four
things that you should understand in
order for for evolution by natural
selection to occur number one there's
mutations so in this case we're talking
about mutations and bacteria so let's
say that we have a population of
bacteria member there's sort of this
this rod shape or sort of look like tic
tacs so you have this population of
bacterial cells but an occasional
bacterial cell will have a mutation
like we see in other populations as well
so we can have a mutation in you know
one particular cell for example this
leads to a new trait so if this
particular mutation causes this bacteria
to be resistant to the antibiotic we
would say that is an adaptation when we
treat a patient with an infection and we
treat them with antibiotics so what
would happen would be a that struggle
for existence that selection process in
this case we would say the selecting
agent would be the antibiotics so if we
treat the patient with antibiotics those
antibiotics will kill this red bacteria
on this red bacteria on this red
bacteria because we would say they are
susceptible to the antibiotics and the
antibiotic successfully killed those
bacteria but this resistant bacteria
persists in the population and what's
gonna happen well he's now he doesn't
have to compete with any of these red
bacteria anymore he's got plenty of room
to grow
he's got the whole lungs to himself and
he's just gonna say great I'm just gonna
start growing in the lungs and so what
what is he gonna do well he's gonna he's
gonna divide okay so he's gonna divide
quickly he's gonna make a whole bunch of
offspring that are identical to him and
we would say now these resistant
bacteria are selected for and now we
have the fourth principle here which
would be evolution survival and
reproduction of the fittest
so the resistant bacteria are free to
divide they will form many resistant
identical resistant cells and the
population has evolved and so in
bacteria because they reproduce so
quickly this can happen very
very quickly and we can end up with
populations of tuberculosis bacteria
that cannot be effectively killed by the
antibiotics that we have available to us
and this is a huge problem because it
means that the bacteria when the
infection
lastly let's talk about some
misconceptions about natural selection
hopefully you don't fall into any of
these misconception traps on the exam
for example we do not say that organisms
develop new traits as a result of a
selection pressure because remember that
is a false that's a false explanation
that was like the Lamarckian view of
evolution which we now know is not how
it works in other words the giraffes
they can't stretch their necks to reach
the leaves up high they're not
developing their traits and that is a
very common misconception I see among
students where they'll say oh well the
organism adapted or they developed this
trait the word develop is not the right
word to you so you want to use the word
evolve okay they evolved each these
traits and how does that work well we
learned today that natural selection is
one of the ways that that works but
important to notice that natural
selection is not creating any new
alleles what creates noozle new alleles
that's a mutation mutation creates new
alleles and this occurs before the
selection pressure so the better way to
describe what happened in the evolution
of the giraffe would be this some
giraffes as a result of random mutation
had longer necks than other giraffes so
there was genetic variation in the
population of giraffes some had long
necks some have short necks and those
with long necks were selected for as a
result of the selection pressure of food
shortage that you needed to reach the
food that was up high so if you happen
to have a long neck you would survive
better than your short-necked giraffe
competitors and then you would pass on
that trait to your offspring in over
time we would see more long necked
giraffes being born than short neck
giraffes and then the population over
many generations would shift in the
characteristics and we would say that
puppy
it involved the third major
misconception I want to get across is
that a particular genetic trait is not
favorable in every environment so
hopefully you got that across with the
bunny simulation for example white
bunnies are better adapted in the Arctic
when they live in the snow and they can
camouflage then brown bunnies but in the
desert environment the brown bunnies
were better adapted so you can't make a
blanket statement like being a brown
colored bunny is always can be the
advantageous trait it's only in that
particular environment is that an
advantageous trait so those are some
misconceptions that I hope you
understand and I hope you understand the
mechanism of natural selection which is
the major mechanism for how evolution
works
