Tip:
Highlight text to annotate it
X
Very briefly I want to discuss the difference between natural and artificial selection as a reminder for you
Very briefly I want to discuss the difference between natural and artificial selection as a reminder for you
when we talk artificial selection we often talk about dog breeds
and at this point within dog breeding we have some major issues that have to be addressed as far as selection of particular
genetics because with the selection of phenotypes that are of interest to breeders'
they may carry along with them some recess of traits that are
not
desired in the
breeding lines so when we talk about pure bred dogs they actually now looking at about 25% of them that have some serious genetic
defect this might be blindness or deafness we also look at things like hip dysplasia
in these breeds but this is all a result of artificial selection -- so artificial selection remember is selection by humans
of some particular characteristic that we like in either dog breeds - cat breeds - agriculture what ever
so what we need to take a minute and think about is if we're looking at variation a population what is the original
source of any new allele in the population or in a species
I don't wanna think about genetic drift
I'm not interested in gene flow
that all occurs after
we have a new source of allele -- so what is that new source?
one other thing we can think about with natural selection
is genetic drift and we've talked genetic draft
genetic drift had two options
that we discussed
read this question
and tell me
what mechanism
could have contributed
to genetic differences between mainland
and Newfoundland moose
write it on your worksheet
so there are still three points that really guide evolution of natural selection
we have to remember the populations evolve -- NOT individuals
we have to look at traits that are heritable
I'm not interested in anything that you cannot pass on to your offspring
so this has to typically be a trait to that is
part of your gametes or at least part of your chromosome set
that is then
through meiosis made part of your gametes
we also ought to think about evolution as not being goal directed -- we can't say I want to be taller
evolution doesn't care
if there's no reason for you to be taller and you don't have the alleles necessary to be taller it's not gonna happen
so will we have to look at
is that
evolution is not going to lead to perfection
here's a prime example
when we look at natural selection
we have to think about it is an editing process
this is not
you're going to dream up the best
organism you possibly can and evolution will get you there -- it's not gonna happen
you have to edit the allele or gene pool that you already have
so by that things are not gonna be perfect
perfection is not an option here
we also ought to look at the fact that natural selection works based on the current environment of a population
so natural selection is only going to work if a trait is favorable
in a population
in a given environment
if you change the population -- you change the environment -- you move that population to a different environment
none of this will hold everything will be
back up for grabs
so we can only work on existing variation so those are our alleles
we have to be limited by what we've inherited from
previous generations
we have to look at the fact that some adaptations are simply compromises so we'll look at
a structure performing many functions -- so with your arm you can wave, you can swim,
you can write things
but are any of those things perfect??
well -- some of them are really good!
but I wouldn't say that any of them are perfect! you can find a way better ways to swim than with that arm you've got sticking out the side
of you, right? and the fact that environments change often very unpredictably - so rapid changes in environment make things even
less perfect. let's look at non perfection!!
this thing is something known as an Archeopteryx
this is what we think is the intermediate between reptiles and birds -- why??
well fathers are birdlike
it's got a beak
well -- but the beak has teeth!
birds don't have teeth most of the time -- there a couple of exceptions but very few
there are claws on the wings!! can you imagine a cardinal flying straight at you with claws coming out of its wings??
that's frightening! one thing you may not know it is
birds don't have vertebrate
out their tail feathers
they have a little stub
a vertebrae -- the tailbone that would attach the feathers that they don't have vertebrae
out their tail -- so this kind of intermediate guy we will look at more later
but I want you to think if evolution was perfect would it have created something like this??
I don't think so!
so when we look at something that's fittest -- so a phenotype that is most fit
what was fitness again??
we have to look at the fact that there is no perfect phenotype
in an environment -- it's the idea that
in the given environment
with the given alleles
we have a possibility to have a good
but not perfect
individual
we will look at the Galapagos finches as I mentioned to you
when we look more at macroevolution because this results in a speciation event
what they looked at
Peter and Rosemary Grant -- looked at changes in the environment and then
looked at resulting phenotypes in bird populations and what they found was
those that actually survived a drought had big beaks! well if you're gonna survive a drought why would you need a big beak??
big beak
means that you can eat harder things right??
harder seeds and so on
after drought plants are going to a very hard seeds produced
so of the survivors of the drought -- so this is the "P" population
of the F1 population their surviving offspring had beaks that were 4 to 5% larger than the "P" population
to this drought so they see this repeatedly over and over and over again
the
pre-beak depth -- so the predrought depth vs. the depth associated with this drought is pretty significant -- so, in 1976
we actually see
the beak height being shorter
depth is actually on the X axis here - and number of individuals is on the Y. so, our pre- beak depth,
pre-drought beak depth is smaller
about 9 1/2 millimeters
but 1978 so after this drought -- this is after drought
we see a shift to a much larger beak depth so about 10 1/4 mm
know you might not think that there's much difference between 9 1/2 and 10 1/4 mm
and under normal conditions you'd be right but
when we look at the depth in birds that's a significant investment in a phenotype to add that much
weight and heft to that beak -- just so that it can eat more seeds
so we'll look at these beak sizes you can look at the differences here -- large ground finch
eating primarily seeds vs. hear a cactus finch that eats primarily small insects
so the difference in the beak sizes huge right and we get this little sharp-billed ground finch what do you think he might eat??
that tiny little beak -- what might he eat?