Discover - USA (2020-01 & 2020-02)

74 DISCOVERMAGAZINE.COM

FRO

M^ T

OP

:^ M

AU

RIC

IO^

AN

TO

N;^

MIR

IAN

KI

LAD

ZE

,^ GE

OR

GIA

N^ N

ATI

ON

AL

MU

SEU

M;^

NA

TU

RA

L^ H

IST

OR

Y^ M

US

EU

M^ O

F^ D

EN

MA

RK

An Old Tooth and a New

View of Evolution

BY GEMMA TARLACH

i

A really old rhino tooth has opened

a new path toward understanding

the tree of life — including, poten-

tially, our own branch.

In September, researchers detailed

in Nature how, using the tooth of a

1.77-million-year-old rhino from the

Republic of Georgia, they were able to

revise its family tree. The team’s success

has implications far beyond rhino ances-

try: It’s proof of concept that it’s possible

to map out evolutionary relationships

between species, with confidence and on

a molecular level, without DNA.

Instead, the team extracted and

sequenced proteins preserved in the

rhino’s tooth enamel.

“Protein sequences are the best

proxy [for DNA],” says University of

Copenhagen’s Enrico Cappellini, lead

author of the study. Cappellini is a special-

ist in paleoproteomics, the study of ancient

proteins preserved in fossils. “In a way,

you can read [proteins] like a text. If you

retrieve only a few words, you can’t read

the story. If you retrieve more words, you

start to understand. And if you have the

ancient and the modern text side by side,

you can see the differences between them.”

Each protein is a unique chain of amino

acids arranged in a specific order. Like

DNA, over time these complex chains

accumulate small changes that can pro-

vide clues to the evolution of a species.

Unlike fragile DNA, ancient proteins can

last for millions of years in fossilized tis-

sues, including bones and teeth.

For years, researchers have been able

Stephanorhinus

called southwestern

Asia home nearly

2 million years ago

(top). The skull of

one of the ancient

rhinos (above)

included a tooth

(left) with preserved

enamel proteins that

researchers could

read like DNA.