[♪ INTRO] 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. [♪ OUTRO]
