hey team alright so we've reached one of
my absolute favorite units in our course
we are now going to be jumping into the
evolution unit this is really exciting
because this is one of the major big
ideas in biology it kind of ties
everything together and then it's also
gonna set us up to talk about all the
different diversity of life on our
planet which is really cool
okay we're gonna define what evolution is
and then we're gonna talk about natural
selection one of the mechanisms of
evolution and then later on we're gonna
jump into other ways that evolution can
happen and then the process of
speciation alright let's get to it I'm
so excited all right so the reason why
evolution is such a big idea is because
it it unifies all of biology together
it's a theory that can explain many
phenomena within biology and many
different aspects of biology can and
really should be viewed through the
in evolutionary lens asking how does
this matter or how does this change when
we think about things in an evolutionary
sense right and that will become more
clear as we move through this unit so
what do we mean by it unifies biology
well evolution the theory of evolution
explains both the unity and the
diversity of life on earth so what does
that mean that means it explains how all
of life is related to each other how it
explains the relation between us and all
other organisms between bacteria and
everything else it explains that we all
share a common ancestor and it also
explains why is there so much life on
our planet to begin with it explains the
diversity of life so it explains why aren't
there just three species why are there
millions upwards of 10 million plus
species on our planet so both of these
big ideas the unity how everything is
related and why are there so many
different forms of life on our planet
both of these can be explained through
the process of evolution through the
lens of evolution so our first big idea
when we're talking about evolution is
this idea of descent with modification
and what that means is that all living
organisms are going to share a common
ancestor
and then through small changes that are
acquired small genetic changes that are
acquired the offspring of that next
generation are going to be slightly
different than their parents and if we
play this idea out those small changes
over long periods of time we can start
to see how all of life is related and
it's through this process of descent
with modification that one ancestor one
living organism common ancestor gave
rise to all of the different forms of
life that we see today on our planet and
this has been documented in the fossil
record and we'll talk about some of the
evidence for evolution including the
fossil record a little bit later on but
how does this happen
right so on a smaller scale we're not
talking about all of life and I'm
talking about on a smaller scale we're
talking about evolution usually within a
population population being all
organisms that are living in a certain
area that are also interbreeding all
right so that's a big idea here
population we measure evolution on the
population level all the organisms
in a given area they're living in that
area together and then also
interbreeding because the interbreeding
is important because that's means
they're gonna be mixing genetic
information okay and so when we see
changes in the frequencies of alleles or
another way to say that when we see over
time
the composition of that population
changes the genetic composition so here
we go this first population we see it's
probably around 90% green beetles in
about 10% Brown beetles right and then
let's say the next generation we see its
flipped we see about like 80% brown
beetles in about 20% green right so that
means that this allele that gene that
allows these beetles to be brown and
this gene that allows these beetles to
be green that allele that frequency how
common it is has changed over a
generation right and that's really how
we're going to be measuring evolution
we're gonna be measuring evolution on a population level and we're
tracking how common or uncommon
in the frequencies of these alleles over
time over many generations so we're
going to talk about one of the key
mechanisms of evolution first we're
going to talk about the mechanism of
evolution that causes adaptive evolution
and that's going to be natural selection
so what does this mean adaptive
evolution
well an adaptation is any characteristic
or trait that increases the likelihood
of an organism to survive and reproduce
in its environment right so adaptations
can take on many different shapes and
forms adaptations in humans could be
things like skin color hair color our
size how tall we are things like that
adaptations in other organisms plants
could be the size of their leaves what
if they have spines or not right or how
efficient they are at bringing in carbon
dioxide and minimizing water last right
so adaptations can be many different
things they can be enzymes they can be
physical structures but this mechanism
that we're going to talk about natural
selection is the only mechanism of
evolution it's the only cause of
evolution that results in adaptive
evolution or organisms being better
suited to their environment being more
likely to survive and reproduce in their
environment right this is kind of what
Darwin and Alfred Russel Wallace are
famous for their famous for coming up
and defining this idea of natural
selection and explaining how species
change over time and how they become
better suited to their environment okay
so there's three major requirements for
natural selection the first being that
characteristics are inherited through
generations okay so we talked about this
we talked about trait inheritance how
offspring are a combination of the genes
from either parent right so we are
similar to our parents but we're not
identical and so these
characteristics these genes Darwin
didn't know about genes at this time but
he saw that offspring are going to be
similar to their parents and that these
characteristics are gonna be inherited
through these generations right so here
we have mama bird feeding these baby
birds baby birds look like mama bird
because they share 50% of the her genes
and so when DNA came on the scene and we
started to figure out that DNA was the
genetic information and that was a huge
breakthrough in evolution because in
order for natural selection in order for
this process this mechanism to act on a
trait to act on a characteristic that
trait must be heritable ok so what that
means is that natural selection can only
function on traits which are inherited
ok it cannot function on traits that are
learned that's a whole other type of
evolution that's cultural evolution or
social evolution we're only focused on
biological evolution right so the trait
must be genetically determined in some
way and it's got to be passed from
parent to offspring our second big idea
in natural selection is that more
offspring are going to be produced every
generation than that environment can
support each individual organism needs a
certain amount of resources to survive
it needs a certain amount of space and
certain amount of food needs a certain
amount of water nutrients whatever right
and so there are more offspring that are
born into every generation than that
environment can support all right so
let's see we have this row of ducklings
here right we have 1 2 3 4 5 6 we have 9
little ducklings sitting right here
right let's say maybe this pond is
really only large enough to produce
seven okay so two of these ducklings
would not be able to survive right and
this is an idea that stems from somebody
called Thomas Malthus which is the idea
that as populations increase in size
they're gonna have a greater demand on
their resources right and he was really
concerned with he wasn't he was an
economist he was concerned with
production of food right and so if
there's not enough food to go around
know everybody's gonna be able to
survive and so that's one of the major
mechanisms that's going to lead to
evolution this is one of the parts of
natural selection that can help lead to
adaptive evolution
alright so traits are heritable more
individuals more offspring are produced
each year each generation than that then
that environment can support and then our
third big idea is that there is
variation in these offspring not all
these offspring are genetically
identical and that variation is
inherited right so let's say of our
ducklings we said 7 we're going to
survive right let's say those seven
that are surviving they are able to
survive because they can swim really
fast and catch lots of food maybe and
the two that aren't able to survive
maybe they didn't get that gene so they
can't swim as fast right maybe they're
there the webbing on their feet isn't as
as extensive so they can't paddle their
feet as fast they can't swim as fast
right
but that variation that we see in this
population is inherited and not all that
variation is gonna be suited to the
environment right but where does that
variation come from originally well we
talked about when we talked about
transcription and translation that
variation arises through mutations so
mutations swapping out letters in that
DNA either through accident in DNA
replication those are going to cause a
change to the gene sequence which can
then result in a different phenotype a
different physical characteristic a
different protein being produced right
so here we have these two cats right
this cat has normal ears it has a
typical normal gene which means it's
gonna produce when that gene is
transcribed and translated it's going to
produce a normally shaped protein versus
this mutated gene over here on the right
we've swapped some of those DNA bases
around they some sort of mutation has
occurred which means that the protein
doesn't form properly anymore which
means now it's ears are gonna be all
folded backwards right so these causes
of these variation can be very diverse it
can be something from the environment
things like UV radiation or carcinogens
or something it can be can be an error
in DNA replicate
or that recombination of genes during
meiosis that swapping of genes that
crossing over that can also lead to
genetic variation as well but whether or
not a mutation is positive negative or
neutral whether it's gonna help the
individual or it's gonna hurt the
individual or it's gonna have no effect
at all it really depends on pon the end
of vironment in which that mutation is
working in right so let's say we have
one mutation for fur color where
that Mouse is white right that mutation
might have a negative impact
if this white mouse is living in a
really dark environment let's say it's
living on black rocks right that white
mouse is gonna stand out versus this
mutation right here that same
environment this black mouse now is
going to be beneficial it's going to be
beneficial environment right so the
environment in which that mutation is
acting is what determines if that
mutation is good or bad or neutral so if
we take all these ideas together
that leaves us we can kind of tie them
all together and that brings us to our
big idea here where those offspring that
are born that have characteristics or traits
to have a genotype and then a phenotype
that allow them to better compete for
access to these limited resources so it
means that they're better at competing
for access for food for access for space
for habitat for mates whatever they need
to survive offspring that are better at
competing for these limited resources as
opposed to offspring that are brought
into that generation that are not as
good as competing those that are better
at competing are more likely to survive
because are more likely to get food and
nutrients and water and space as opposed
to those that are not as likely to
survive okay as opposed to those that
are not as likely to compete as well and
those that are more likely to compete
better they're more likely to survive
and they can also reproduce at a higher
rate which means they're gonna have a
higher Fitness a greater Fitness right
so this idea of Fitness is that those
individuals with genotypes
that are better suited for environment
genotypes and phenotypes that are better
suited for an environment are more
likely to survive and therefore
reproduce right so Fitness is all about
reproduction it's all about the number
of offspring that an individual produces
in that number of offspring an
individual produces is based on the
combination of genes that it has and the
characteristics that it inherited all
right so that's our big picture view of
natural selection then one of the
mechanisms that leads to adaptive
evolution
