BBC Wildlife - UK (2020-04)

BBC Wildlife 77

EVOLUTION

April 2020

and their ‘big tusk genes’ fromthe

gene pool. Now elephants areevolving

smaller tusks, or sometimes,no

tusks at all. Over a period of 20 years,

the proportion of tuskless female

elephants in Zambia’s SouthLuangwa

National Park increased from 10 to 40

per cent, all because of ivory poaching.

Invasive species are leaving their

mark, too. Venomous Argentine fire ants

were introduced to the southern United

States more than 70 years ago, where

they now prey on the resident fence

lizards. In response, the lizards have

evolved longer hind legs to help them run

away. Cane toads are also evolving longer

limbs, which are helping them expand

their range in Australia. Meanwhile, two

Australian snake species that eat cane

toads have evolved smaller heads. These

petite-skulled reptiles can’t physically eat

the larger, more toxic amphibians, so they

are more likely to survive.

When Darwin thought about evolution,

he envisaged changes taking place over

achingly long time periods. He wrote,

“We see nothing of these slow changes

in progress, until the hand of time has

marked the long lapse of ages,” and for

In New York, it seems

white-footed mice have

been evolving the ability

to eat pizza and peanuts.

the most part this is true. However, when

the environment changes rapidly, the

pressures driving natural selection are

so persistent and intense, that evolution

shifts from first into fifth gear. We are

now witnessing evolutionary change

over human time frames of decades and

centuries, rather than geological time

frames of millennia and millions of years,

all because of human activity. The world

hasn’t seen evolutionary change on this

scale since the demise of the dinosaurs.

For better or worse?

When we breed domestic species or

tweak the DNA of animals in laboratories,

we change evolution on a local scale. The

genetic fallout is limited to those animals

that we can physically touch, but now, as

we alter the world at a global level, we are

inadvertently influencing the evolution

of all living things, near and far. There

may well be some ice-dwelling Antarctic

microbe that is blissfully immune to

our actions, but as the world warms and

the ice melts, this innocence will not

last. Humans are now influencing the

evolution of all life on Earth.

So what to make of it all? Some species

will evolve themselves out of trouble, but

many will not. The large and slow-

breeding are most at risk, butit’snotall

doom and gloom. Conserva

stories, like the recent rise

numbers, teach us how do

evolutionary spirals can sometimes be

rerouted onto a positive incline. Humans

are fuelling the demise of the natural

world, but we are unique in that our

species has the insight and technology to

turn things around. Life is always

changing, but with humans at the helm

• guided by science and the need to
  protect the planet we live on – we can
  help life to change for the better.

HELEN PILCHER explores these
ideas further in her new book, Life
Changing: How Humans are Altering
Underground: Getty; feeder: Tim Gainey/Alamy; swallows: Marie Read/NPL/Alamy; ferret: USDA Photo/Alamy; lizard: Robert Eastman/Alamy Life on Earth, published by Bloomsbury.

becameeroded,groupsofmice found

themselvesisolatedinthecity’s various

parks.They,too,evolvedalong different

trajectories,andnowmicein Manhattan

aregeneticallydifferentto mice from

QueensandtheRockawayPeninsula.

Not just that, the critters also show

signs of adapting to city life. White-

footed mice in Central Park carry

unusual versions of genes that help

them process fatty foods and neutralise

a toxic fungus found on mouldy nuts.

In the time since the mice have been

isolated in the city’s famous green space,

it seems they have been evolving the

ability to eat pizza and peanuts!

Size is everything

Meanwhile in Nebraska, American cliff

swallows have evolved smaller wings,

which help them to dodge the traffic

on the busy roads and bridges where

they build their nests. In Puerto Rico,

city-dwelling crested anole lizards have

evolved longer legs and stickier toes to

help them cling to buildings, whilst

on our own home turf, great tits are

evolving longer beaks because it helps

them snaffle peanuts from bird feeders.

Urban life is causing species to change.

Hunting is another human activity that

is causing animals to evolve. In Africa,

when poachers target the elephants with

the biggest tusks, they remove them

Right: things are

looking up for the

crested anole lizard,

which has evolved to

scale buildings.

Far left: Tube stations sheltered

many (including mosquitoes)

during the Blitz. Bottom left:

American cli swallows are

downsizing their wings. Below: a

longer beak benefits the great tit.