- [Dr. Samuel] Hi everybody, Dr. Samuel here,
your friendly neighborhood entomologist.
And I was hoping that we could take a few minutes
to talk about adaptation.
What comes to mind when you think about adaptation?
You might think of cryptic morphology
that helps organisms hide from predators,
scaly armor or spines to protect organisms in a scuffle,
or increased melanin pigmentation in the skin
to shield an organism from the damaging impacts
of harsh sunlight in really sunny areas.
And if this is the sort of thing that you thought of,
you're right, these are all adaptations.
But what people often miss about adaptations
is that they all help organisms survive and reproduce
in a particular environment.
The word adaptation can refer to a trait
that makes an organism more suited to its environment.
But it can also mean
the process by which a population
becomes dominated by organisms
that are suited to their environment.
The point is that adaptation happens in a population
as its organisms accumulate adaptations.
And this all happens through the process
of natural selection,
which you may have heard about.
With natural selection, we see organisms
with beneficial heritable traits,
increasing their share of the gene pool in the population
because they're more likely to mate and produce offspring.
This means these well-adapted organisms have higher fitness,
a measure of an organism's ability
to survive and reproduce
in its specific environment.
These traits or adaptations make the organisms better suited
to survive and reproduce
because they're better suited
to the specific environmental context that they live in.
That is our green caterpillars blend in,
and thus, survive better on the green leaves,
and the orange caterpillars on the orange leaves.
As you can see, natural selection
is intimately intertwined with the environment
in which it takes place.
And this is why natural selection can lead to adaptation.
Even the concept of adaptation is diverse.
Adaptations can be anatomical,
changes to physical structures, or physiological,
changes in the function of these structures,
or adaptations can be changes to behavior.
We see this with honeybees adapted to life in Africa,
sometimes called by the suboptimal names,
Africanized honeybees or killer bees.
They're the same species as and look identical too.
Populations of honeybees adapted to North America,
but their behaviors diverge dramatically.
Because the African populations
are adapted to life in a hot, tropical environment,
sometimes, they construct nests right out in the open air,
nests in open air.
This is extremely rare for populations
adapted to the temperate climate of North America,
where the temperature range is far too broad
between winter and summer for open air nests
to be successful.
So, North American honeybee populations
much prefer to live inside of protected structures
like inside of the trunks of hollow trees
or the boxes that beekeepers provide,
nests in protected structures.
And in Africa,
there are also more large, fearsome predators
interested in getting into the bees' nest.
So, the frequency of traits related to hyper defensiveness
is much more common
than in populations adapted to North America,
where there are fewer aggressive predators,
heightened defensiveness, low
to moderate defensiveness.
The success of honeybees adapted to life in Africa
left a lot of people worried
that they would be similarly successful in North America
and replace the honeybees there.
But those concerns ignored the connection
between adaptation and the environment.
Traits that helped those bees survive in Africa
and even helped them in similar environments
found in many regions of tropical,
South and Central America,
well, those same exact traits
were liabilities in much of North America.
Okay, so, this is all fascinating,
but you may be wondering,
if natural selection is passing out adaptations,
why doesn't it choose better stuff?
Fish tend to get eaten by birds and bears a lot.
And that's gone on for literally millions of years.
So, why I haven't fish populations
developed something like laser eyes or teleportation?
Instead, when a population of fish does evolve defense,
it's typically something like a few bones,
that it already has, getting longer and sharper
and protruding out of their fins,
like in the case of the three-spined stickleback fish.
These spines protect the stickleback
from birds and other predators,
but only if the spines are long enough
to make it difficult for that specific predator
to swallow them.
Birds with wider throats are still able to eat
even fully grown fish with fully elongated spines.
Laser eyes really do seem like they would be more effective.
It's almost like natural selection
is just tinkering with whatever it has lying around
instead of going out and buying something new
and perfectly suited to the task.
And that is exactly what's happening.
Populations don't adapt by accessing a bottomless well
of awesome problem-solving options.
Quite the contrary, with natural selection as the driver,
adaptations can be pretty limited.
You might already be tracking with the idea
that if an increase in fitness
is what natural selection is after,
you don't need an adaptation that allows you to incinerate
all of your enemies.
You just need one good enough to solve whatever problem
is keeping others in your population
from surviving in mating.
If that's a kingfisher bird eating the other fish,
the resolution might be just a spine
that's only a half a centimeter longer
than the other fishes.
That's the reason why we see adaptations
that look like natural selection just grabbed
whatever happened to be lying around and modified it
because it kinda did.
A turtle's remarkably protective shell
may look fancy and novel,
but it's literally the turtle's overgrown ribs
fused with its spine.
A narwhal's face spear,
that there is just a tooth
that grew all the way out of its face.
Natural selection only has the options
currently in the genes of a population
with the occasional addition
of new genetic sequences through mutation
to work with when a problem arises.
And you might be thinking, "Oh great!
Mutations, those will help!
That's how my favorite superhero got her powers."
Well, unlike what we see in movies,
most mutations either have no real effect
or result in problematic gene expression
or nonfunctional proteins
which is pretty bad news for living things.
So, adaptations are not likely to be super weapons
that ensure survival in all circumstances.
Instead, they're useful traits
that help increase an organism's fitness
as the environmental conditions apply pressure.
So, adaptation is a remarkable system,
but one with some pretty pronounced limitations.
Natural selection has to work with what an organism has.
But consider for a moment what it has given us
despite those limitations.
Pistol shrimp have the ability
to slam their claws shut so quickly
that the water around them collapses in on itself.
It implodes knocking nearby fish unconscious.
Some honeybees can bundle together
and vibrate their flight muscles so rapidly
that they can create a biological convection oven
which can cook predators to death.
And there are parasitic wasps
that have evolved to live inside of parasitic wasps
that live inside of parasitic wasps
that live inside of caterpillars,
like tiny, strange, little Russian nesting dolls.
And don't even get me started on the hornets
that have yellow patches on their abdomen
that absorb solar energy
to supplement the energy provided by their diet.
They have solar panels!
I'd say natural selection has done pretty well for itself.