New Scientist - USA (2013-06-08)

8 June 2013 | NewScientist | 9

In this section

n Deadly skin cancer reversed by immune therapy, page 12

n Time cloak deletes chunks of history, page 14

n Mind-controlled exoskeleton, page 19

environments to expand into.

“You get more insects and fruit

in an equatorial climate. They

benefited from that.”

How, then, did Africa end up

being the cradle of humanity?

If the out-of-Asia hypothesis is

correct, early monkey-like

primates must have moved from

Asia over to Africa, sometime

around 40 million years ago,

Beard says. The hypothesis must

still explain how they made the

move, crossing the vast Tethys Sea

which separated Asia and Africa.

As Jaeger puts it: “It is difficult

to imagine small mammals

surviving on a raft for two weeks

in the sun.”

However, the extreme heat of

the PETM, and the lingering

warmth over the next few million

years, could have helped, says

Thierry Smith of the Royal Belgian

Institute of Natural Sciences in

Brussels. The high temperatures

would have created lush tropical

forests that spanned continents.

Early tree-dwelling primates

could only have spread through

such forests. “A tarsier on the

ground is prey, because it cannot

walk. It’s like a crab, it’s terrible.”

However it happened, the

move would prove to be a pivotal

moment in our history.

“[Primates] underwent a real

starburst of evolution in Africa,

which eventually led to apes and

humans,” says Beard.

We can expect to hear much

more about that first colonisation

of Africa in the near future.

“Humanity’s spread out of Africa

was undoubtedly very important,

but it wouldn’t have happened if

our primate ancestors hadn’t got

into Africa in the first place,” says

Beard. “The ‘Into Africa’ story is

very big right now – and it’s only

going to get bigger.” n

Additional reporting by Michael

Marshall

Finding Archie

The fossil of Archicebus achilles is the oldest primate skeleton ever found. Analysis

so far places it in the tarsier lineage but it may yet turn out to be a human ancestor

Monkeys

Tarsiers

Lemurs

and lorises

Dinosaur extinctionPalaeocene-EoceneThermal Maximum

Archicebus achilles

?

“Lucy”

70 60 50 40 30 20 10 0

Millions of years ago

“Ida” Darwinius masillae

Homo

sapiens

Homo erectus

Homo habilis

Australopithecus

Chimpanzee

Gibbons

Orang-Utan

Gorilla

“Humanity’s spread out

of Africa wouldn’t have

happened if primates

hadn’t got into Africa first”

Since Archicebus is so old, many will

wonder if it is a “missing link” – the

species that gave rise to all primates

alive today. The answer is a confusing

mix of “yes”, “no” and “maybe”.

No Archicebus is probably not the

ultimate link in our primate family

tree. Finding that animal is remarkably

difficult, because the earliest

chapters of the primate story have

left hardly any good fossils. While

Archicebus is an exciting find, it is not

an ancestor of lemurs and lorises, as

the evolutionary tree above shows.

There may be an older, more

primitive primate out there waiting

to be discovered.

Some readers may remember a

47-million-year-old fossil unveiled

in May 2009. Nicknamed Ida, it was

touted as this missing link. Most

biologists now think it is no more

than an early member of the lemur

and loris family.

YeS Archicebus lies very close to

the junction between tarsiers and

monkeys, apes and humans. It could

be as close as we are ever likely to get

to the missing link between these

two important groups of primates.

MAYbe For now, Archicebus lies on

the tarsier side of the tree. If and

when more good fossils from this

period are found, it is possible it

might flip onto our side (see main

story). Until we can fill in more of the

picture, though, it’s a bit of a stretch

to call it one of our missing links.

tHe elusIve ‘mIssIng lInk’

p 11): the trait, it seems, may trace

all the way back to an animal very

like Archicebus.

At the moment, analysis of

Archicebus places it not on our

direct line, but with our next-door

neighbours, the tarsiers of south-

east Asia (see chart, right). “But it

is incredibly close to the junction,

and it wouldn’t take much to flip

it over to our side of the tree,”

says Beard. “I wouldn’t be totally

shocked if in future we were to

find out that Archicebus is a basal

anthropoid [the group comprising

monkeys, apes and humans].”

He has one main reason for

believing Archicebus is closer

to home than he can prove at

present. Parts of its body are eerily

similar to what we would expect

to find in our oldest ancestor. Its

ankle bone, in particular, looks

just like a monkey’s – a feature

that led the team to name the

remarkable fossil after the Greek

hero Achilles.

Jean-Jacques Jaeger of the

University of Poitiers in France

agrees that Archicebus’s mix of

tarsier and anthropoid traits

make it hard to say which group it

belongs to. It could also turn out

to have belonged to a third group

that didn’t survive, he adds.

There are no other good primate

fossils from this far back in time.

Until we can compare it with its

peers, says Beard, Archicebus’s

exact place in the tree is going

to be unclear. “We’re almost

operating in a vacuum here.”

Perhaps most significantly, the

new fossil supports the idea that

primates originally evolved in

south-east Asia, and suggests the

ancestors of all monkeys and apes

had already split off from other

primates 55 million years ago –

millions of years earlier than

textbooks suggest. “Many of us

suspected that was the case,” says

Beard. “Archicebus solidifies that

this important branching event

goes right back to the beginning

of the Eocene.”

This links the birth of our

primate line to a major spike in

global temperatures known as

the Palaeocene-Eocene Thermal

Maximum (PETM). It also puts

our point of origin squarely in

the heart of the PETM furnace:

equatorial Asia. “Primates are

probably the most tropically

adapted mammals alive today,”

says Beard. It therefore makes

sense that they originated in a

warm climate.

What’s more, south-east Asia

would have offered a refuge for

tropical species to weather the

storm of cooler times: while

Earth’s drifting tectonic plates

dragged all major continents

across the latitudes, this region

remained where it was, right on

the equator.

“There were so many ecological

niches available in those forests

[after the extinction of the

dinosaurs 65 million years ago],”

says Jaeger. Hot temperatures, he

adds, may have provided primates

and other mammals with rich

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