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[ ♫ INTRO ]
We tend to talk about the evolution of species as something
that happened in some ancient time.
Almost as if all species evolved to their modern forms
and just… stopped.
But evolution is a never-ending process.
And while we humans are still evolving ourselves, our existence
is also driving the evolution of many other species.
From mosquitos to coyotes, species from all walks of life are evolving
because of ways we’ve influenced the environment.
Today we’ll look at five of them.
One major way that humans are influencing the environment
is through urbanization: essentially, turning rural areas into cities and towns.
Urbanization can have all sorts of consequences for the species in an area,
starting with habitat loss.
As forests, swamps, and other natural environments
are bulldozed to make way for concrete jungles,
many plant and animal populations disappear.
But some luckier species are able to make themselves
at home in their new environment.
Coyotes are a great example of this.
Coyotes are native to North America, west of the Mississippi.
And in the 1800s, as U.S. settlers moved westward
and built up towns and cities, they started breaking up coyotes’ natural habitat.
In response, some coyotes relocated to less populated areas.
But some stayed put… and actually learned to thrive in human cities.
And even though they’re not naturally nocturnal,
some started looking for food at night to avoid humans.
And they happily adopted human food as their own.
In a 2020 study, researchers looked at the diets of coyotes living in the Los Angeles area
by analyzing food in their poop and trace elements in their whiskers.
And they found that up to 38% urban coyotes’ diets consisted of human food,
most of which they likely fished out of the trash.
They supplemented this with a mouthful of birdseed or ornamental fruit…
or Pet cats.
So basically, coyotes are doing more than fine.
They’ve even spread east and made surprisingly successful homes out of places like New York City.
But this change in lifestyle has changed coyotes themselves.
As they adapted to their new, fractured habitats,
different groups stopped mating with each other,
so their gene pools became isolated.
Over time, these coyotes have evolved into genetically distinct populations.
Today, thanks to urbanization,
there are distant rural populations of coyotes
that are more genetically similar to each other than rural
and urban populations that live side by side.
Coyotes aren’t the only animals that have responded to urbanization
by making themselves at home in cities.
Another is the white ibis.
That’s a wading bird related to egrets and storks
that lives along the coasts of the southeastern U.S.
It’s also found along the coasts of Mexico and Central America.
Naturally, white ibises hang out in estuaries and shallow wetlands…
but in the last century, their natural habitats have gotten developed by humans.
And rather than crowd into dwindling wetlands,
some have adopted cities as their new homes.
Because, like urban coyotes, ibises learned that living around humans
means living around food.
These birds spend a lot of their time eating handouts from people
as well as scraps from dumpsters and garbage cans.
The ibis has a long, gently curved bill
that originally evolved for plucking things like insects
and crabs out of the mud.
But it happens to be pretty handy for foraging through garbage too.
Unfortunately, while ibises love our garbage,
it’s low in the essential nutrients and protein
that they need for survival, and higher in carbs.
This poor nutrition can change the types of bacteria living in their guts,
much like an unbalanced diet changes the bacteria in the human digestive system.
Researchers have also found that the birds’ diet of garbage
is also associated with higher levels of pathogens like Salmonella.
That doesn’t always bother the birds,
but they can transmit these pathogens to humans if the two come in contact.
Fortunately for them, preliminary research suggests that,
in spite of their poor diets, so far city ibises don’t seem to be any worse for the wear.
Some researchers even found that urban ibises are
better off than their rural counterparts in a few ways.
For instance, eating literal trash toughens up their immune systems,
so they’re better at fighting off bacteria like E. coli.
They’re also less stressed,
possibly because finding garbage to eat is so much easier than hunting.
And researchers have noticed that they also have fewer parasites, which may be
because they have more time to clean themselves since they’re not working so hard to find food.
Researchers have yet to determine whether these changes are just behavioral,
or if any of them reflect a genetic change.
Whichever it is, we’re forcing ibises to adapt quickly
to a fast changing environment.
Many of the animals that hang out in cities have specifically adapted
to those unnatural environments and get along pretty well.
But while the arrangement might work out for them,
it’s not always great for the people in those cities.
Today, humans around the world are plagued
by an especially annoying species of mosquito,
with a special taste for human blood. Its name is literally Latin for “annoying mosquito.”
But this pest hasn’t always been around. It appears to have evolved in just the last few
hundred years, from another species of mosquito that only bites birds.
For a long time, researchers believed that it’s evolution
into the annoying mosquito happened in the London Underground.
According to the lore, it got trapped down there in the 19th century
and adapted to suck other creatures’ blood for survival,
gradually evolving into a separate species.
And a study conducted in the late 1990s did find
that the mosquitoes living in the London Underground are a separate species
from the mosquitoes that live aboveground.
But a 2022 study found that the same species
found underground in London already existed in the late 1700s in Egypt,
almost 100 years before the London Underground was built.
The authors of that study speculated that these mosquitoes actually arose there.
Thanks to the long history of agriculture in the region,
there were plenty of damp, enclosed spaces like root cellars where they could breed,
plus lots of humans to feast on.
Basically, they found a niche to fill, so they diverged from their bird-biting ancestors.
It’s hard to verify the exact history behind the rise of this mosquito,
but one thing is pretty clear: It had to do with humans.
Regardless of whether it arose in the London Underground or old Egyptian cities,
this particular mosquito thrives in spaces humans have created,
like damp underground cellars, sewers, and subways.
So, thanks to changes we’ve made to the environment,
we will probably always be living right alongside them.
Now, urbanization isn’t the only driver of recent species evolution.
Long before big cities existed, humans were already making their mark on some species.
And one big way they did that was through fishing.
For thousands of years, humans have cast their nets or their rods in search of large
, hearty fish that would make a good meal.
And our methods have typically relied on fish being bold enough
to go after a hook or swim into a net.
So, more often than not, we’ve taken the biggest,
boldest fish out of the population first.
As a result, people’s fishing practices
have shaped the evolution of species we like to fish.
In populations that get fished a lot, survival of the fittest favors timid, smaller fish,
which are less desirable to humans and less likely to get themselves caught.
In a four-year study, carried out between 2007 and 2010, researchers in Europe
actually measured the differences between various populations of northern pike
living in a lake in Germany.
By assessing the differences, researchers hoped
to understand the effects on populations that had been heavily fished.
So, for four years, they caught fish, marked them, and collected data on them.
Then they released them back into the water.
By the end of the study, they found that they had
caught, and marked, bigger, bolder fish,
and the population not sampled was smaller and shyer.
Had they actually been removing those fish, rather than releasing them,
the small, shy fish would have been the only ones left to breed.
This shows how, over time, fishing practices have changed the course of this species’ evolution,
and the same may be true of other commonly fished species too.
This may not seem like a big deal, and researchers
haven’t yet explored the impacts in detail.
But one thing we do know is that food webs are incredibly complex,
and a shift in the size and behavior of a population could have far-reaching consequences
for both this species and the ones that depend on it.
These are some of the less obvious consequences of fishing and hunting by humans.
But the northern pike isn’t the only species to go through a change like this.
The bighorn sheep, a species found in mountainous regions in North America,
went through a similar population shift.
From the early 1970s until 2011, people heavily hunted rams, or male bighorn sheep,
living on Ram Mountain in Alberta, Canada.
These rams were killed for their horns, which are famously long and curly.
But only certain rams were legally allowed to be hunted.
Their horns had to reach a certain length and curl before they could be killed as a trophy.
It takes time to grow horns that long, and some rams grow them faster than others.
The big guys with the fanciest horns were
between 4 and 7 years old by the time their horns reached the legal length.
The problem was, by this point, the rams hadn’t reached
the peak of their success in mating, which comes between the ages of 8 and 10.
So trophy hunting wiped out the large-horned males
before they came of age and could pass on their genes to the next generation.
A group of researchers in Canada analyzed almost 40 years’ worth of data,
including 23 years of intense hunting
, to better understand the consequences of this selective pressure on bighorn sheep populations.
And they found that the average size of horns in their study area declined
by over 20% in the 40-year study period.
That happened because hunting practices
were knocking out the larger-horned males before they could reproduce,
while the smaller males kept contributing to the gene pool.
Not only that, but since the most intensive hunting stopped in 1996,
bighorn sheep’s horns have yet to return to their previous length,
hinting at a permanent change in the genetic makeup of this population.
These sheep are just one example of many animals being hunted
for their size and paying the price evolutionarily.
And it underscores just how wide-ranging and profound humans’ effect on other species can be.
By selectively killing organisms that have traits we value,
or by building cities in their natural habitats,
we accelerate changes that would otherwise happen through natural selection.
Almost everything we do as humans has the potential
for an accidental evolutionary consequence.
So, it’s important to remember and factor into our conservation plans,
every time we harvest resources and develop land.
While some harvests may impact evolution, they’re still a huge part of our daily lives.
After all, we’ve got to eat.
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