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How well do we know

ourselves? The fossil record

of hominins, our ancestors and

closest kin, is limited, and the

exploration of our collective deep

history through genetic analysis is

still a relatively new field. Neither

excavations nor lab work has been

able to reconstruct, definitively,

the earliest chapter of the Homo

sapiens story.

For decades, two competing

models of human evolution have

dominated the field. One claims

that H. sapiens evolved in a

single place, Africa, and left that

continent only fairly recently; the

other suggests that our species

evolved in multiple regions across

both Africa and Eurasia.

While debate between

proponents of the two models

rages on, there’s one big problem:

Researchers keep finding fossil and

genomic evidence that don’t fit

either model.

A paleoanthropological review

published in Science in December

acknowledged that the evidence

had reached a tipping point. It’s

time, the authors said, for a new

model of how our species evolved

and spread across the world. But

how does this new model compare

with its predecessors?^ D

Gemma Tarlach is senior editor at Discover.

Our

New Past

Amid competing models

of human evolution,

a more complex story

of our species emerges.

BY GEMMA TARLACH

RECENT AFRICA

ORIGIN MODEL

Beginning in the mid-20th

century, fossils unearthed in

Africa showed a progression, over

millions of years, from a primitive

bipedal primate to anatomically

modern humans. Based on those

fossils, researchers developed

the Recent Africa Origin (RAO)

model for human evolution and

migration. According to the RAO

model, although some groups of

our predecessor Homo erectus

left Africa roughly 2 million

years ago, those early explorers

eventually died out and did

not contribute significantly to

modern human ancestry. Instead,

H. sapiens evolved exclusively

in Africa and left the continent

only about 60,000 years ago to

spread across Eurasia. The RAO

model has dominated Western

thinking about human evolution

for decades.

MULTIREGIONALISM

MODEL

The RAO model does not account

for some hominin fossils found

outside of Africa, especially in

China, that are 100,000 years or

older but appear to belong to

anatomically modern humans.

Based on these fossils and some

artifacts, a challenge to RAO

emerged: multiregionalism.

According to this model, after

H. erectus populations left

Africa roughly 2 million years

ago, these intrepid hominins

settled in pockets across Eurasia,

where they continued to evolve

into regional populations of H.

sapiens. Multiregionalism agrees

with one aspect of RAO: When

the relative latecomer sapiens

left Africa 60,000 years ago

and met up with other hominin

populations in Eurasia, some

interbreeding occurred. According

to multiregionalists, however, the

ancestry of human populations

outside of Africa, particularly

in Asia, is rooted in the earlier

regional H. erectus populations.

60,000

years ago

2 million

years ago

2 million

years ago

60,000

years ago

EUROPE ASIA

AFRICA

EUROPE

ASIA

AFRICA

QHOMO SAPIENS QHOMO ERECTUS Interbreeding

Anatomically modern human teeth about

100,000 years old, found in Daoxian, China,

challenge the Recent Africa Origin model.

Origin

Story