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Evolution has been helping animals survive for millions of years,
and it works partially because it’s a long, slow process.
Natural change tends to happen at a snail’s pace, which gives animals
a lot of time to adapt and develop new survival strategies.
Then humans came along, and we messed up pretty much everything.
Humans change things fast. We tear down forests, throw garbage around,
build dams, and set up exotic species in new habitats.
That’s not always a bad thing, but native species can have a hard time
adapting to those rapid changes.
And sometimes, they end up falling into an evolutionary trap,
which is a technical term! It’s what happens when a species makes
a seemingly-illogical decision that’s triggered by
a rapid change to its environment.
To humans, these choices seem really dumb, but they’re usually
right in line with whatever survival strategies the species
has depended on in the past.
First, these fancy beetles deserve their fancy name.
Australian jewel beetles are golden brown and kind of sparkly.
Kind of like brown tourmaline… or this one kind of beer bottle.
In fact, the Australian jewel beetle actually looks a lot like
this one specific beer bottle that was made in Australia in the 1980s,
called a “stubbie” by the locals.
So that’s kind of a fun coincidence... except it caused a major problem.
Back when stubbies were common road litter, the males beetles
would mistake them for females and try to mate with them.
And we’re not just talking about the occasional,
adorably-confused teenaged beetle.
A lot of these males seemed to prefer stubbies over real females,
to the point of actual mortal peril.
But from a biological perspective, this behavior isn’t irrational.
The female jewel beetle is considerably larger than the male.
And the bigger the female, the more attractive she is to the males.
These beetles also have little bumps on their forewings that sparkle
in the sunlight.
Bumps that are really, really similar to the bumps
at the base of a stubbie.
They even reflect light in the same way.
So a male jewel beetle flying along in a search for a mate would
see one of these discarded stubbies and think to itself,
“Holy giant girlfriend!”
In fact, the males were so enamored that they would not only
try to mate with the bottles, they would keep trying
until they collapsed from exhaustion.
Then, in some cases, they would fall off the bottles…
and get eaten by ants.
Alas, this story does actually have a happy ending.
When the company that manufactured the stubbies learned about
the tragic romance, they changed the design of their bottles
and made them bump-free.
So now, the males have gone back to, you know, actual female beetles.
We humans rely on our brains to give us information about
the food we eat.
You know, like “cake: good” and “kale: bad.”
Or maybe it’s the other way around.
At any rate, we know what’s edible and what’s not because we keep
that information tucked away in our brains for future reference.
But other animals don’t do food in quite the same way.
They rely more on their senses to tell what’s good to eat
and what isn’t.
Take sea turtles, for example.
Like a few other ocean dwellers, sea turtles often eat plastic,
which seems like… I don’t know, maybe not the smartest move.
No matter how you prepare it, plastic is just not good for you.
In fact, it can be deadly.
Still, studies suggest that more than half of all sea turtles
have eaten it in varying quantities.
And that’s because they’re tricked by their senses.
A floating plastic bag, for example, can look a lot like a jellyfish —
something turtles normally eat.
But it can also smell like something edible.
Research suggests that plastic that’s been in the ocean a long time
gets taken over by organisms like algae and other tiny creatures.
After a while, those creatures give the plastic the same odor profile
as the food turtles eat naturally.
So these unfortunate turtles can’t really smell the difference
between old plastic waste and actual food.
And plastic hasn’t been around long enough for them to develop
other ways to figure out it’s no good to eat.
So! Find a recycling bin!
Or you know, just use less plastic if that’s an option.
Next, dragonflies!
Dragonflies and many other aquatic insects lay their eggs in
or very close to water.
And to complete this part of their life cycle, they need
to accomplish one simple task: They have to find the water.
It seems straightforward, and it’s clearly gone well for millions
of dragonfly generations.
But some of the more modern insects seem a bit confused.
They’ll lay their eggs on a lot of surfaces, and many of them
aren’t even wet. Like asphalt. Or glass. Or solar panels.
Or even one very weird case of dragonflies hitting up tombstones
in a graveyard.
Then, the eggs die of course, because the nymphs need water to grow.
Now, this new habit of laying eggs on dry things seems bizarre
until you know how dragonflies actually find water.
The secret is, they search for water using polarized light
— that is, light waves that vibrate in a certain direction.
The horizontal surface of a body of water reflects light
in a mostly-horizontal direction.
And that’s what the dragonflies are looking for.
That’s actually reasonable, because until recently,
there wasn’t much in nature that reflected light in quite the same way
as a body of water.
Until humans came along.
The anthropogenic world is full of things that reflect light
but are not water.
Like asphalt, glass, solar panels, and the occasional
shiny, black headstone.
So modern dragonflies, who are confused by all the sparkle,
will often lay their eggs on those reflective things instead of water.
Again, the problem here is that dragonflies haven’t evolved fast enough
to figure out the difference between artificial, shiny things
and natural ones.
So it’s up to us to make sure that the things we put out into
the world don’t catch their eye.
For example, a simple white border around a solar panel seems
to have a deterrent effect.
Which won’t solve all the dragonflies’ problems,
but it’s a good start.
Monarch butterflies like things to be just so.
The adults aren’t super picky about what they eat,
but they are really, really picky about where they lay their eggs
and where their kids grow up.
In fact, there is only one sort of plant that will do: milkweed.
Milkweed not only nourishes their caterpillars, but it also
contains toxic compounds called cardenolides that accumulate
in the caterpillars’ tissues and make them taste bad.
So birds and other predators leave them alone, which is pretty smart.
But lately, monarchs have been doing something that seems
kind of dumb.
They’ve been laying their eggs on a type of milkweed that
is terrible for their caterpillars.
This tropical milkweed is popular with gardeners, but it’s not
the same stuff that’s naturally found in the monarch’s habitat.
Tropical milkweed produces greater concentrations of cardenolides
in warmer temperatures.
And too much of the toxin seems to be associated
with a reduction in adult monarch’s survival.
That’s not a huge problem today, but as the climate warms,
monarch caterpillars that eat this variety might be less likely to survive.
Except, the monarchs don’t know that.
In fact, to make things more complicated, the caterpillars
that dine on tropical milkweed can sometimes grow up to be
larger, stronger butterflies.
That is, if it’s not too warm.
And if they don’t encounter any of the other problems
with tropical milkweed.
Like, this plant helps spread a common but dangerous parasite,
and it can thrive during the wrong season, which messes up
the monarch’s natural migration and breeding calendar.
So in seeking to do what they’ve always done, monarch butterflies may
end up making choices that are bad for the survival of their species.
Finally, not all evolutionary traps are set by human beings —
maybe thankfully.
Sometimes biology seems to back itself into a corner,
and a species will become stuck.
Such is the case of the black-headed duck.
This kind of duck is an obligate brood parasite, like the
brown-headed cowbird or the notorious cuckoo.
Like those birds, this duck doesn’t incubate its own eggs
or care for its own young.
Instead, it lays its eggs in the nests of other birds —
usually red-gartered or red-fronted coots — who are duped
into providing surrogate services.
Unlike the cowbird and the cuckoo, though, the black-headed duck
is a much more polite brood parasite.
Birds forced to care for cowbird or cuckoo chicks pay the price
in the form of wasted energy and resources — and often the lives
of their own young.
But black-headed duck babies are precocial, which means they’re
ready to care for themselves just a day or two after they hatch.
So, they’re really not much of a pain for their surrogate parents,
but that doesn’t seem to matter to the coots.
More frequently than ever, researchers are seeing the hosts reject
the duck eggs by burying them in their nests instead of
sitting on them and incubating them.
And this is happening so often that, in the future, there might
not be enough eggs hatching to support a healthy population of ducks.
But, alas, the ducks keep showing up.
And they just keep laying their doomed eggs in coot nests.
And, like, they’re not even sneaky about it, either.
Their eggs are plain white and pretty easy to spot
in a nest of speckled coot eggs.
You’d think that they would have learned by now, but like with
these other ecological traps, they just haven’t had time.
See, until recently, this whole parasite gig was going really well.
So well that not a single black-headed duck ever had
to build a nest of its own.
Coots would accept enough duck eggs that the entire species could continue.
So, the strategy was a smart one. Lazy, but smart.
And then things changed — not with the ducks, but with the coots.
Researchers think the red-gartered and red-fronted coots are
now parasitizing the nests of other members of their own species.
Brood parasitism, as it turns out, is actually a pretty useful way
to make sure more of your offspring survive.
But if you’re the host, well, raising someone else’s chicks is expensive.
So the coots are getting better at spotting imposters,
even amongst eggs that look exactly like their own.
Which means that the duck eggs are even more glaringly alien
in a coot nest, and more likely to get rejected.
This is a relatively new change, though, so the ducks keep laying
their eggs in coot nests. Mostly, because they don’t have a choice.
Black-headed ducks don’t know how to make their own nests,
and the rapid change in coots’ behavior hasn’t given them enough time
to develop strategies, like laying eggs
that more closely resemble coot eggs.
So unless someone provides the ducks with a library copy of
What to Expect when You’re About to Lay an Egg,
their parenting philosophy isn’t going to change any time soon.
Sometimes, humans can shut down these evolutionary traps before
they drive a whole species to extinction — like when the beer bottle
makers stopped putting those sexy bumps on the bottles.
We can also find ways to discourage these behaviors,
like throwing less garbage in the ocean.
But sometimes, like in the case of the ducks, nature is just
going to be nature, and it's going to set its own rules.
Still, no matter what causes these ecological traps,
there’s usually something we can do to help protect these
misguided species from us. And themselves.
If you want to hear more weird facts about the universe,
you might like our podcast, SciShow Tangents.
We’ve been referring to it as a “lightly competitive knowledge showcase,”
but really, it’s just a good time.
It’s produced by Complexly and WNYC Studios, and it features four
of the people who’ve made SciShow happen over the years:
Hank, Stefan, Sam Schultz, and Ceri Riley.
The four of them spend each episode showing off their best
science knowledge and going on a few good tangents along the way.
If you want to check it out, you can find SciShow Tangents wherever
you get your podcasts, or by clicking the link in the description.
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