Hi guys this is part three of chapter 12.
I want to tell you about artificial
selection and natural selection. So this
first slide is about artificial
selection and how we humans can actually
artificially alter allele frequencies.
And this is an interesting slide it
shows you the wild mustard the yellow
flower here you know that's the one that
grows along the highway 1 there
Davenport that area where the fields and
spring are really beautiful because
they're all yellow
that's wild mustard and botanists have
bred that over and over and over again.
And when they've bred it for stems for
those plants that have the strongest
stems and flowers you end up with
broccoli and when you breed it for
lateral buds so when it has little tiny
buds at the side and then you breed it
with another one that has lots of those
and you breathe it again with another
one that has lots of those you end up
with Brussels sprouts. And just like that
they've taken this wild mustard, bred it
over and over again and created
cauliflower, kale, cabbage, all these come
from an artificial selection of the wild
mustard plant called Brassica oleracea.
So you know in animal husbandry we've
been doing this for years also getting
animals and breeding them for fat or for
horns or for greater milk production and
that artificial selection we've done
over and over again. So when it comes to
natural selection, how is that happening
on its own? So that's also descent with
modification right the change that's
happened it's modified like the gradual
change of the finches over time on the
Galapagos Islands, it integrates the
thoughts of Malthus his idea in
populations and how they grow. So if you
have a limit on populations a limit of
food a limit of how many can
the organisms can grow in a particular
area then there's going to be
competition because if you have too many
individuals then what's gonna happen is
they're gonna be competing. And if there's
competition then you have to win
essentially. And winning means being the
best adapted to that environment so that
you can feed better than anybody else
you can find a mate better than anybody
else and you can get ahead essentially
and this is what organisms do they try
and give ahead. So that concept of
natural selection then rises from this
and the thought of differential
reproductive success it means not only
will you feed more not only will you do
better in this environment but you will
probably leave a greater number of
offspring because you will be able to
reproduce successfully whether you're a
plant or an animal so that's very
important is how well you do to live and
also to leave offspring. Humans to are
a species competing for resources.
So any adaptation that you think of
enhances reproductive success. Success
but think of it as natural selection
doesn't really create a change like I
showed you these camouflaged insects.
Natural selection doesn't purposely
create that instead its selects for that
camouflage and alleles that rise by
chance their selecting in the in the event
of a change happening and one particular
organism having these little red tips
here that looks like a dying leaf a
little bit that one let's say that
organism does really well because he
doesn't get eaten because the birds
really confuse him with a leaf and so
guess what? If he doesn't get eaten he
gets to leave more offspring because he
gets to live and mate and leave more
offspring. So natural selection isn't
creating the change but it is selecting
once it finds an organism that does
better
it's going to leave more offspring in
the next generation. So I'm saying in the
slide some individuals are better than
others
at surviving and reproducing so they can
obtain nutrients, they can
obtain water, they don't get eaten, they
maybe tolerate temperature changes, they
attract mates, they reproduce, they're
doing well. So they're successful
essentially. So we think that since
more individuals are born then resources
can support that struggle to survive is
going to be inevitable. If it's a
struggle then you've got to get ahead
somehow. This is just a dandelion that's
leaving hundreds of seeds. They look
like little parachutes that take off and
they're going to land and leave seeds
somewhere else and that reproductive
manner is very successful make lots of
seeds and blow them in lots of
directions and have many more dandelions
on in everybody else's lawn. So I'm
going to show you two slides now ones
called the logic of natural selection
and then the next one is the inference
from those observations. Let me
backtrack. The logic of natural selection,
the observation then that we're
noticing is that there is genetic
variation. Within a species no two
individuals are exactly alike. So some
are going to be more adapted some are
going to do better if they're different.
Two, there are limited resources every
habitat contains limited supplies of the
resources required for survival so it's
going to be competitive and if you do
better you're gonna outsmart the other
organism then you're the one that's
gonna leave more offspring. Three, over
production of offspring more individuals
are born and survive to reproduce so the
dandelion all those seeds very few of
them
are going to make it but if you over produce those
seeds then it is more likely that some
of them will make it. So this is
what we observe in nature. So 'what?' is
what comes next. So what about those
observations. Well number one this is
struggle for existence individuals
compete for the limited resources. Two,
unequal reproductive success. So maybe one
dandelion it was tiny and wimpier and put
out fewer seeds is going to leave fewer
offspring than the other dandelion that
was big and maybe it was in a place
where there was more water and was able
to put out more seed and do better.
So it's an unequal reproductive success.
Some will do better than others. Three,
says descent with modification, over many
generations natural selection can change
the characteristics of populations even
giving rise to new species. So if all of
a sudden I have that leaf with the brown
edges and they didn't used to have brown
edges but one ended up with brown edges
left many offspring those offspring left
many offspring and those offspring left
even more then there's going to be a
change in the characteristics of that
population
all of a sudden more of the population
is going to have that brown edge 
to the insect looking more like a leaf.
Some organisms do this super well and
sometimes they're thought of as a super
organism. Think of roaches. Roaches do
really well, they live everywhere, they
feed on everything, they invade,
especially in the tropics, they can
invade any kitchen any place that has
food and do leave lots of offspring. Rats
in New York City, they have taken over
right they do super well and they're
very well adapted
leave lots of offspring. We're gonna
consider them a superorganism maybe. The
meaning of fitness that word fitness is
very important because we talk about it
in terms of survival of the fittest. So
to be fit what does that mean in
biological terms. It doesn't mean to be
big and strong. For example, this
aunt the Argentinian ant invaded
California and it has completely
decimated the populations of horned
toads it gets into their little holes it
attacks the toads these lizards and it
destroys those populations so it's not
that they're big and strong but that
they have been able to successfully
carve out this little niche for
themselves. To be fit in biology
means to leave lots of offspring. The
classic example I give is the honeybee
drones because this is a male honeybee
here and what they do in a hive in a
colony all they need to do is mate with
new Queens with virgin Queens and leave
their genes in the next population that
would increase their fitness. But it
turns out that they can't always do that
because they can't find a queen so they
have no fitness at all and when they do
find a queen and they can mate with a
queen
they will have their genes go on in the
next generation that while mating or
after mating they die. So a dead drone
bee that has left its genes in the next
population has a greater fitness than
the one that lived and never mated. Is
that weird you guys? I'm going to stop
there.
