THE “OUT OF AFRICA” THEORY

Vicky Lee

CHARLES DARWIN’S PREDICTION

The Descent of Man“In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.”

BACKGROUND INFORMATION

Early species of Homo, Homo habilis, evolved in Africa around 2 million years ago

Later, Homo erectus evolved along with other hominids and migrated out of Africa

Homo erectus evolved to Homo sapiens around 100,000 to 200,000 years ago

WHAT IS THE THEORY?

A distinct group of sub-Saharan Homo sapiens inhabited Africa for about 150,000 years before migrating throughout other continents

Homo sapiens completely replaced all earlier human populations (Neanderthals and Homo erectus)

No interbreeding occurred

“OUT OF AFRICA”

FOUNDATION OF THE THEORY

Emerged in 1987 based on a study of mitochondrial DNA (mtDNA) Rebecca Cann

Genetic studies & fossil record Andrea Manica Marcus Feldman

GENETIC STUDIESCann mtDNA is key

Inherited through mother, does not recombine, and shows variation within gene pool from mutations only

Restriction mapping Analyzed mtDNA from 147 people living

among five different geographic populations All populations except African have multiple

origins implying each area was colonized repeatedly

GENETIC STUDIES

Cann Molecular clock

Assumes mtDNA sequence divergence accumulates at a constant rate

Timescale calculates age of hypothetical common ancestor “Mitochondrial Eve” to be about 140,000-225,000 years old

Evolutionary tree Diagram of 133 types of mtDNA Inferred that Africa had the most diverse

mtDNA gene pool

EVOLUTIONARY TREE

GENETIC STUDIES

Manica Found that Africans have the highest

genetic variation The further humans migrated from

Africa, the more genetic diversity was lost within those populations

GENETIC STUDIES

Feldman Studied genetic ancestry without

identifying where the population came from

Interpreted that mixed ancestries caused by recent intermixing shared common ancestry before the

divergence of two populations but without any additional gene flow between them

GENETIC STUDIES

Feldman Found same conclusion as Manica

study, less variation the further humans go from Africa

No single genetic marker can identify a person’s race patterns of thousands of genetic markers

within the group distinguishes one population from another

FOSSIL RECORD

Manica Analysis of skulls from populations on

different continents The further away from Africa the skulls came

from, the less variation found in physical features compared with African skulls

Population bottleneck As more and more groups migrated further,

smaller parts of genetic variation were taken

THE RIVAL THEORY

Multiculturalism Created by anthropologist Franz

Weidenreich Does not believe that there were two

migrations Homo erectus migrated out of Africa

and then evolved into Homo sapiens in several populations

Interbreeding did occur

MULTIREGIONALISM

SUMMARY OF “OUT OF AFRICA” THEORY Homo sapiens completely replaced all

earlier human populations (Neanderthals and Homo erectus)

No interbreeding occurred The further humans migrated from Africa,

the more genetic diversity was lost within those populations

Age of hypothetical common ancestor “Mitochondrial Eve” is 140,000-225,000 years

REFERENCES

Cann, Rebecca L., Mark Stoneking, and Allan C. Wilson. "Mitochondrial DNA and human evolution." Nature 1 Jan. 1987: 31-36.

Connor, Steve. "How old is humanity, and where did 'Homo sapiens' come from?; The big question." The Independent (London) 19 Jan. 2007: 1A.

Darwin, Charles. The Descent of Man. < http://www.literature.org/authors/darwin-charles/the-descent-of-man/chapter-06.html>.

Feldman, Marcus et al. "Worldwide Human Relationships Inferred from Genome-Wide Patterns of Variation." Science 16 Nov. 2008.

Hua Liu, et al. A Geographically Explicit Genetic Model of Worldwide Human-Settlement History. The American Journal of Human Genetics, volume 79 (2006), pages 230–237

Johanson, Donald. "Origins of Modern Humans: Multiregional or Out of Africa?" Action Bioscience. May 2001. American Institute of Biological Science. 4 Nov. 2008

<http://www.actionbioscience.org/evolution/johanson.html>. Pennisi, Elizabeth. "HUMAN EVOLUTION: Genetic Study Shakes Up Out of Africa Theory."

Science 19 Mar. 1999: 1828. Roach, John. "Massive Genetic Study Supports "Out of Africa" Theory." National Geographic

21 Feb. 2008. Templeton, Alan R. "GENETICS AND RECENT HUMAN EVOLUTION." The Society for the

Study of Evolution 2007: 1507-1519. Wong, Kate. "Is Out-of-Africa Going Out The Door?" Scientific American Aug. 1999.