discovered so far (Nature Genetics, DOI: 10.1038/ng1914). Some were

expressed very rarely.

“The brain has 10,000 cell

types,” says team member Edwin

Cuppen. “Perhaps that is because

of all these micro-RNAs.” Many

were unique to chimps and

humans, and some only to

humans. So even though we share

most of our DNA with chimps,

small genetic changes that fine-

tune its expression might account

for the radical differences in our

brains. “This is the playground of

evolution,” says Cuppen.

the messenger RNA that

translates DNA into protein.

This allows them to fine-tune

gene expression. Discovered only

a few years ago, micro-RNA has

been shown to determine what

cell types form, and, for example,

whether sheep become muscular

or puny.

Now, researchers at the

Hubrecht Laboratory in Utrecht,

the Netherlands, have combed

painstakingly through the RNA

in human and chimp brains,

and found 447 new micro-RNAs,

more than doubling the number

HOPES of a male contraceptive

with no serious side effects have

come a step closer to fulfilment.

Chuen-Yan Cheng at the Center

for Biomedical Research in New

York City and his colleagues have

previously found that a drug

called Adjudin blocked fertility

in male rats by disrupting the

interaction between the germ

cells that produce sperm and the

Sertoli cells that nurture their

development. But when given to

rats orally, Adjudin caused liver

inflammation and muscle

deterioration. “Even though it was

very effective, we couldn’t make

use of it,” says Cheng.

His team has now coupled

Adjudin to a mutant form of

follicle-stimulating hormone

(FSH), a hormone that targets

the testes and triggers sperm

development, and says this

avoided the side effects (Nature Medicine, DOI: 10.1038/nm1420).

When they injected it into the

rats it stopped sperm production,

rendering the rats infertile about

4 weeks later. The effects of the

drug wore off about 8 weeks after

that. Since regular injections of

contraceptive are unlikely to

prove popular in people, the team

is now developing a gel patch.

Sperm blocker beats side effects

IT HAS been described as a snake

threaded through the body of a turtle,

and some imaginative people think

there’s one living in Loch Ness.

The plesiosaur, a marine reptile

that lived 160 million years ago,

looked like nothing alive today, with

a neck that was some 2 metres long,

the length of the body and tail

combined. Why it needed such a long

neck has been a mystery, but now

Leslie Noè of the Sedgwick Museum in

Cambridge, UK, has an answer.

Plesiosaurs used their long

necks to reach down and feed on

soft-bodied animals living on the

sea floor, Noè told the Society of

Vertebrate Paleontology meeting in

Ottawa, Canada, last month.

He examined fossils of a plesiosaur

called Muraenosaurus, and by

calculating the articulation of the

neck bones he concluded the neck

was flexible and could move most

easily when pointing down. “The

neck was a feeding tube, collecting

soft-bodied prey,” he says. The small

skulls of plesiosaurs couldn’t cope

with hard-shelled prey.

He also has some disappointing

news. “The osteology of the neck

makes it absolutely certain that the

plesiosaur could not lift its head up

swan-like out of the water,” Noè says,

ruling the reptile out as a candidate

for the Loch Ness monster.

APES do it, we do it… and so, it seems,

do elephants. They can recognise

themselves in a mirror, passing a test

of self-awareness that is failed even

by most of our primate relatives.

Until recently, this ability was

thought to be the exclusive preserve

of humans and great apes.

Then in 2001, Diana Reiss of Columbia

University in New York showed

that dolphins tended to position

themselves to view a mark on their

bodies that would not otherwise be

visible, showing that they too could

recognise their own reflections.

Like humans and apes, dolphins

are highly social animals with large

brains, and seem to show empathy

towards one another. So Reiss turned

her attention to another large-brained

and apparently empathetic species –

the Asian elephant. Teaming up with

Frans de Waal and Joshua Plotnik of

Emory University in Atlanta, Georgia,

Reiss presented three elephants at

the Bronx Zoo in New York City with

a mirror. They began inspecting

themselves with their trunks while

staring at their reflections, and one

repeatedly touched a mark painted

onto its head (Proceedings of the National Academy of Sciences, DOI:

10.1073/pnas.0608062103).

A previous attempt to investigate

self-recognition failed, apparently

because the mirrors used were too

small. “Elephants don’t have the best

eyesight,” de Waal says. “It’s

important that the mirror is the size

of an elephant and is accessible.”

MICRO-RNA, snippets of RNA

that control gene expression,

could be what makes the difference

between us and chimps.

Variation between individuals,

in traits ranging from pigment

to behaviour, is the raw material

of evolution. The difference can

be down to very subtle changes:

the genes involved may code for

exactly the same proteins but

make them at other places and

times. So could micro-RNA be

the determining factor?

Micro-RNAs are a mere

22 nucleotides long and block

THEO

ALL

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Humans left chimps behind in ‘evolution’s playground’

www.newscientist.com 4 November 2006 | NewScientist | 17

Elephants recognise their mirror image

Why Nessie is no plesiosaur

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