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So what isn't an adaptation?
I've given you lots of examples of things
that result from selection and therefore are called adaptations.
And Doug Futuyma, one of the countries, United States, best well know evolutionary
biologist, you know, he points out it's an outcome of the selective process.
And we've given you a number of examples, not only in natural selection but sexual
selection, where phenotype changes as a result of a selective process.
And it's a process also he says, of
genetic change in a population whereby as result of
natural selection, the average state of a character becomes
improved with reference to a specific function and outcome.
And actually where, where we think this function has a, creates a better fit,
so to speak, fitness between the organism and the environment.
1:14
some people would say, well there's
selection for individuals, and those individuals carry
properties, and therefore it's not the properties,
it's the individuals that that are selected.
But in,
selection is basically that these properties allow,
because they are selected for, they, they
contribute to the overall fitness of individuals,
leaving more offspring in the next generation.
And then, natural selection can be seen as a filter for amongst individuals.
and for the genes of those that
those individuals carry for any particular trait.
Now we, we, we infer,
in many instances one can see change in phenotype through
time, and one then, therefore infers that
somehow or other that phenotype is conveying greater fitness.
But one has to demonstrate that through experimentation, because some properties
can go along for the ride.
So, they can be genetically linked to other properties, so you
can pro, you can select for property A, and then property D,
C and F are, are linked genetically to A, and they too
will change, but yet they are not the locus of natural selection.
2:36
Now, how does one recognize an adaptation in nature?
Lots and lots of things are said, oh, that's an adaptation for, because they see
an organism doing something, using that feature,
and therefore they just assume it's an adaptation.
And, so if they see complex structures
they, they think it might be an adaptation.
And, if there's a function associated with these traits,
then that too is seen as potentially an adaptation.
And if
we have models, like we did with the sexual selection, if they
fit the predictions in the models, we can say that they're adaptations.
And we can do it through experimentation like we like we saw with the bird tales.
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And another comparative way of looking at adaptation is that
if we see parallel changes in different unrelated groups of organisms to the same
environment, then we say those are adaptations.
So in the Arctic, in the wintertime, many birds and mammals change from a brown
plumage or pellage in the summertime, to a very white one in the wintertime.
And the idea here is, of course, that
they're blending in with a snowy background, and, therefore,
trying in that way avoid a predation.
And that seems to be a way in which one can look at traits across
different groups of organisms and say why are those there and, comparatively.
But, let's take a really interesting example, and I, and I like to use this
because it, it seems to show experimentally that there's selection
for, for an adaptation, and that's the bill tip.
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So, in almost all birds, there is a little
projection of the upper mandible on, over the lower mandible.
And you, you know that in hawks
and eagles, that it's really really projects strongly.
So we can see in this example, a really cool experiment.
So on the right hand side, it shows that they trimmed
the, this little appendage, this little projection off of pigeons.
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the red group, and they increase, they, they,
they just left the green group just like that.
And what happened is the, when this grew back,
and this is just like a, a fingernail, it, it
continually is growing, when this grew back, they started
to reduce the number of lice on them by preening.
So,
if you go out in the parks, you'll see birds preening all the time.
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So, the inference here, the inference here is that,
in fact, this is an adaptation to preen lice away.
But the problem is, is that this is a primitive condition.
This, this is found in lots and lots and lots and lots of birds,
and a, and a lot of birds that don't have lice issues.
And other people have said, well this is really just to help them preen.
6:15
And then other people say, well this has evolved to help them get food.
And certainly, you can easily imagine that that's the case with raptorial birds.
So, is this really an adaptation or not? This experiment would suggest,
oh yes, an adaptation for getting rid of lice.
But on the other hand, you, you see that bill in a lot of species
that do not have a major forms of lice, and this is a primitive condition.
So if you look through the evolutionary history of birds,
this was has been around for a long, long time.
So there's other things that this might be the function
might be, like for just simply preening the plumage, getting
it in order so flight is easier and so forth.
So, we have to think about, do we just, when we see these structures, we can't
automatically say this is an adaptation for something for a particular function.
Because often these have a long history and
they have a multi-functional purposes. So adaptation is a wonderful thing.
We, we see it all the time, it's
pervasive, but we also need very good experimental evidence
and deep study on the genetics of it, to
really nail down whether things are adaptations or not.
Joel Cracraft, Ph.D.Chair and Lamont Curator
David Randle, Ph.D.Senior Manager of Professional Development
