How animals and plants are evolving in cities Menno Schilthuizen
Transcriber: Ivana Korom
Reviewer: Krystian Aparta
This is where I grew up.
A small village near the city of Rotterdam
in the Netherlands.
In the 1970s and 1980s,
when I was a teenager,
this area was still a quiet place.
It was full of farms and fields
and swampland,
and I spent my free time there,
enjoying myself,
painting oil paintings like this one,
collecting wildflowers, bird-watching
and also collecting insects.
And this was one of my prized finds.
This is a very special beetle,
an amazing beetle called an ant beetle.
And this is a kind of beetle
that lives its entire life
inside an ant’s nest.
It has evolved to speak ant.
It’s using the same chemical signals,
the same smells as the ants do,
for communicating,
and right now, this beetle
is telling this worker ant,
“Hey, I’m also a worker ant,
I’m hungry, please feed me.”
And the ant complies,
because the beetle is using
the same chemicals.
Over these millions of years,
this beetle has evolved a way
to live inside an ant society.
Over the years,
when I was living in that village,
I collected 20,000 different beetles,
and I built a collection
of pinned beetles.
And this got me interested,
at a very early age, in evolution.
How do all those different forms,
how does all this diversity come about?
So I became an evolutionary biologist,
like Charles Darwin.
And like Charles Darwin,
I also soon became frustrated
by the fact that evolution is something
that happened mostly in the past.
We study the patterns that we see today,
trying to understand the evolution
that took place in the past,
but we can never actually see it
taking place in real time.
We cannot observe it.
As Darwin himself already said,
“We see nothing of these slow
changes in progress,
until the hand of time
has marked the lapse of ages.”
Or do we?
Over the past few decades,
evolutionary biologists
have come to realize that sometimes,
evolution proceeds much faster
and it can actually be observed,
especially when the environment
changes drastically
and the need to adapt is great.
And of course, these days,
great environmental changes
are usually caused by us.
We mow, we irrigate, we plow, we build,
we pump greenhouse gases
into the atmosphere
that change the climate.
We release exotic plants and animals
in places where they didn’t live before,
and we harvest fish and trees and game
for our food and other needs.
And all these environmental changes
reach their epicenter in cities.
Cities form a completely new habitat
that we have created.
And we clothe it in brick and concrete
and glass and steel,
which are impervious surfaces
that plants can only root in
with the greatest difficulty.
Also in cities, we find
the greatest concentrations
of chemical pollution,
of artificial light and noise.
And we find wild mixtures
of plants and animals
from all over the world
that live in the city,
because they have escaped
from the gardening
and aquarium and pet trade.
And what does a species do
when it lives in a completely
changed environment?
Well, many, of course, go, sadly, extinct.
But the ones that don’t go extinct,
they adapt in spectacular ways.
Biologists these days
are beginning to realize
that cities are today’s
pressure cookers of evolution.
These are places
where wild animals and plants
are evolving under our eyes very rapidly
to suit these new, urban conditions.
Exactly like the ant beetle did
millions of years ago,
when it moved inside an ant colony.
We now find animals and plants
that have moved inside the human colony
and are adapting to our cities.
And in doing so,
we’re also beginning to realize
that evolution can actually
proceed very fast.
It does not always take
the long lapse of ages;
it can happen under our very eyes.
This, for example,
is the white-footed mouse.
This is a native mammal
from the area around New York,
and more than 400 years ago,
before the city was built,
this mouse lived everywhere.
But these days, they are stuck
in little islands of green,
the city’s parks, surrounded by a sea
of tarmac and traffic.
A bit like a modern-day version
of Darwin’s finches on the Galapagos.
And like Darwin’s finches,
the mice in each separate park
have started evolving,
have started to become
different from each other.
And this is my colleague,
Jason Munshi-South,
from Fordham University,
who is studying this process.
He is studying the DNA
of the white-footed mice
in New York City’s parks,
and trying to understand
how they are beginning to evolve
in that archipelago of islands.
And he’s using a kind of
DNA fingerprinting, and he says,
“If somebody gives me a mouse,
doesn’t tell me where it’s from,
just by looking at its DNA,
I can tell exactly
from which park it comes.”
That’s how different they have become.
And Jason has also discovered
that those changes,
these evolutionary changes,
are not random, they mean something.
For example, in Central Park,
we find that the mice have evolved genes
that allow them to deal
with very fatty food.
Human food.
Twenty-five million people
visit Central Park each year.
It’s the most heavily visited park
in North America.
And those people leave behind snack food
and peanuts and junk food,
and the mice have started feeding on that,
and it’s a completely different diet
than what they’re used to,
and over the years,
they have evolved to suit
this very fatty, very human diet.
And this is another city slicker animal.
This is the European garden snail.
A very common snail,
it comes in all kinds of color variations,
ranging from pale yellow to dark brown.
And those colors are completely determined
by the snail’s DNA.
And those colors also determine
the heat management of the snail
that lives inside that shell.
For example, a snail
that sits in the sunlight,
in the bright sun,
if it has a pale yellow shell,
it doesn’t heat up as much as a snail
that sits inside a dark brown shell.
Just like when you’re sitting
in a white car, you stay cooler
than when you’re sitting
inside a black car.
Now there is a phenomenon called
the urban heat islands,
which means that in the center
of a big city,
the temperature can be
several degrees higher
than outside of the big city.
That has to do with the fact
that you have these concentrations
of millions of people,
and all their activities
and their machineries,
they generate heat.
Also, the wind is blocked
by the tall buildings,
and all the steel and brick
and concrete absorb the solar heat
and they radiate it out at night.
So you get this bubble of hot air
in the center of a big city,
and my students and I figured
that maybe those garden snails,
with their variable shells,
are adapting to the urban heat islands.
Maybe in the center of a city,
we find that the shell color is evolving
in a direction to reduce
overheating of the snails.
And to study this, we started
a citizen-science project.
We built a free smartphone app,
which allowed people
all over the Netherlands
to take pictures of snails
in their garden, in their street,
also in the countryside,
and upload them to a citizen
science web platform.
And over a year, we got 10,000 pictures
of snails that had been photographed
in the Netherlands,
and when we started analyzing the results,
we found that indeed,
our suspicions were confirmed.
In the center of the urban heat islands,
we find that the snails have evolved
more yellow, more lighter-colored shells.
Now the city snail and the Manhattan mouse
are just two examples
of a growing list of animals and plants
that have evolved to suit
this new habitat,
this city habitat that we have created.
And in a book that I’ve written
about this subject,
the subject of urban evolution,
I give many more examples.
For example, weeds that have evolved seeds
that are better at germinating
on the pavement.
Grasshoppers that have evolved a song
that has a higher pitch
when they live close to noisy traffic.
Mosquitoes that have evolved
to feed on the blood of human commuters
inside metro stations.
And even the common city pigeon
that has evolved ways to detox themselves
from heavy-metal pollution
by putting it in their feathers.
Biologists like myself,
all over the world,
are becoming interested
in this fascinating process
of urban evolution.
We are realizing that we’re really
at a unique event
in the history of life on earth.
A completely new ecosystem
that is evolving and adapting
to a habitat that we have created.
And not just academics –
we’re also beginning to enlist
the millions of pairs of hands
and ears and eyes
that are present in the city.
Citizen scientists, schoolchildren –
together with them,
we are building
a global observation network
which allows us to watch this process
of urban evolution taking place
in real time.
And at the same time,
this also makes it clear to people
that evolution is not
just some abstract thing
that you need to travel
to the Galapagos to study,
or that you need to be a paleontologist
to understand what it is.
It’s a very ordinary biological process
that’s taking place
all the time, everywhere.
In your backyard,
in the street where you live,
right outside of this theater.
But there is, of course,
a flip side to my enthusiasm.
When I go back to the village
where I grew up,
I no longer find those fields and swamps
that I knew from my youth.
The village has now been absorbed
by the growing
conglomeration of Rotterdam,
and instead, I find shopping malls
and I find suburbs and bus lanes.
And many of the animals and plants
that I was so accustomed to
have disappeared,
including perhaps that ant beetle.
But I take comfort in the fact
that the children growing up
in that village today
may no longer be experiencing
that traditional nature
that I grew up with,
but they’re surrounded
by a new type of nature,
a new type of ecosystem,
that, to them, might be just as exciting
as the old type was to me.
They are living in a new,
modern-day Galapagos.
And by teaming up with citizen scientists
and with evolutionary
biologists like myself,
they might become the Darwins
of the 21st century,
studying urban evolution.
Thank you.
(Applause)