Evolution And History

206 CHAPTER 9 | The Global Expansion of Homo sapiens and Their Technology

The Recent African Origins or

“Eve” Hypothesis

The recent African origins or “Eve” hypothesis (also called

the out of Africa hypothesis) states that anatomically mod-

ern humans are descended from one specific population of

Homo sapiens, replacing not just the Neandertals but other

populations of archaic H. sapiens as our ancestors spread

out of their original homeland. This idea did not originate

from fossils, but from a relatively new technique that uses

mitochondrial DNA (mtDNA) to reconstruct family trees.

Unlike nuclear DNA (in the cell nucleus), mtDNA is

located in the mitochondria, the cellular structures that

produce the energy needed to keep cells alive. Because

sperm contribute virtually no mtDNA to the fertilized

egg, mtDNA is inherited essentially from one’s mother

and is not subject to recombination through meiosis and

fertilization with each succeeding generation as is nuclear

DNA. Therefore, changes in mtDNA over time occur only

through mutation. By comparing the mtDNA of living

individuals from diverse geographic populations, anthro-

pologists and molecular biologists seek to determine when

and where modern H. sapiens originated (Figure 9.1).

throughout the parts of the world inhabited by mem-
bers of the genus Homo. By contrast, those supporting
a theory of recent African origins argue that all contem-
porary peoples are derived from one single population
of archaic H. sapiens from Africa. This model proposes
that the improved cultural capabilities of anatomically
modern humans allowed this group to replace other ar-
chaic forms as they began to migrate out of Africa some-
time after 100,000 years ago. Both theories are explored
in detail below.

The Multiregional Hypothesis

As several anthropologists have noted, African, Chinese,
and southeastern Asian fossils of archaic Homo sapi-
ens imply continuity within these respective popula-
tions, from H. erectus through to modern H. sapiens;^4
this lends strong support to the interpretation that there
was genetic continuity in these regions. For example, in
China, Pleistocene fossils from the genus Homo consis-
tently have small forward-facing cheeks and flatter faces
than their contemporaries elsewhere, as is still true to-
day. In Southeast Asia and Australia, by contrast, skulls
are consistently robust, with huge cheeks and forward
projection of the jaws.
In this model, gene flow among populations keeps
the human species unified throughout the Pleistocene.
No speciation events remove ancestral populations such
as H. erectus or Neandertals from the line leading to
H. sapiens. Although proponents of the multiregional
hypothesis accept the idea of continuity from the earli-
est European fossils through the Neandertals to living
people, many other paleoanthropologists reject the idea
that Neandertals were involved in the ancestry of mod-
ern Europeans.

OH

OL

PH

PhePL

D-loop

Pro

Thr

Cyt b Glu

ND6

ND5

ND4

Leu(UCN)

Leu(UUR)

16S

rRNA

12S

rRNA

Ser(UCN)

His

Arg

Gly

COX III

COX II

COX I

AT P 6

AT P 8

Lys

Ty r

Asp

Tr p

ND2

ND1

Met

Ile Gly

Val

Ala

Cys

Asp

ND41

ND3

Ser(AGY)

Figure 9.1 The 16,569 bases in mitochondrial DNA

(mtDNA) are organized into circular chromosomes present

in large numbers in every cell. The human mtDNA sequence

has been entirely sequenced, with functional genes identi-

fied. Because mtDNA is maternally inherited and not subject

to recombination, it can be used to establish evolutionary

relationships. However, population size impacts the preser-

vation of variation in the mtDNA genome and complicates

using contemporary mtDNA variation to calibrate a molecu-

lar clock.

multiregional hypothesis The hypothesis that modern

humans originated through a process of simultaneous local

transition from Homo erectus to Homo sapiens throughout the

inhabited world.

recent African origins or “Eve” hypothesis The hypoth-

esis that all modern people are derived from one single popula-

tion of archaic Homo sapiens from Africa who migrated out of

Africa after 100,000 years ago, replacing all other archaic forms

due to their superior cultural capabilities; also called the out of

Africa hypothesis.

(^4) Wolpoff, M. H., Wu, X. Z., & Thorne, A. G. (1984). Modern Homo sapiens
origins: A general theory of hominid evolution involving fossil evidence
from East Asia (pp. 411–483). In F. H. Smith & F. Spencer (Eds.), The ori-
gins of modern humans. New York: Alan R. Liss; Wolpoff & Caspari; Pope,
G. G. (1992). Craniofacial evidence for the origin of modern humans in
China. Yearbook of Physical Anthropology 35, 291.