Out-of-Africa Theory:
The Origin Of Modern Humans
Presented By
Adrian Padilla
Background Information
• First species of Homo, Homo habilis,
evolved in Africa around 2 million years
ago.
• Later, a descendant of Homo habilis,
Homo erectus evolved (along with other
hominids), and spread out of Africa.
• Homo erectus gave rise to Homo sapiens
around 100,000 to 200,000 years ago.
Two Main Theories
• Out of Africa Theory (OOA) – suggests that
Homo erectus evolved into Homo sapiens in
Africa, and then ventured out of Africa and
dispersed to all around the world.
• Multi-regional Evolution Theory – suggests
that Homo erectus ventured out of Africa and
then evolved into modern man in several
different locations through out the world.
Genetic Tools to Find the Answer
• Fossil records
• DNA sequencing
– Mitochondrial DNA analysis (mtDNA)
• Maternally inherited, therefore telling the story from the
female side of human history
– Y Chromosome analysis
• Inherited down the paternal line, complementing the mtDNA
– Microsatellite DNA analysis
• Segments of tandemly repeated DNA with a short repeat
length, usually 2-5 nucleotides
Polymorphisms
• Polymorphism - Existence of a gene in
several allelic forms.
• Polymorphic regions provide a very unique
set of genetic markers for studying human
origin and migratory patterns.
• Used to construct a global evolutionary
tree of modern man
Mitochondrial DNA
• Out-of-Africa hypothesis was first sketched
out in 1987, based on mitochondrial DNA
analysis
• Suggested that modern man first
appeared on the scene in eastern Africa
about 150,000 years ago, and left
between 35,000 and 89,000 years ago,
eventually conquering the globe.
Y Chromosomal DNA Study
• Researchers looked at DNA samples from
12,000 male Y chromosomes in Asia.
• Looking for 3 specific mutations on the Y
chromosome known to have originated in
Africa.
• Researches found that every one of the
12,000 samples carried one of the three
mutations or polymorphism
Conclusion to the Y Chromosome
Study
• Little or no interbreeding of Homo erectus and
•
•
•
Homo sapiens.
Individuals are descendants from Africa
Likely that the early African man emigrated to
North Africa and made the leap to Asia and then
to the rest of the world.
Indicates that modern humans of African origin
completely replaced earlier populations in East
Asia.
More Y Chromosomal Studies
• Samples were taken from men in 22 different
geographical areas.
– In countries that included Pakistan and India,
Cambodia and Laos, Australia and New Guinea,
America, Mali, Sudan, Ethiopia and Japan.
• Researchers identified 167 polymorphic markers
•
on the Y chromosome.
Markers were then assembled into 10 types,
called haplogroups.
Findings from Y Chromosomal
Analysis
• Assembled a phylogenetic tree showing a migration from eastern
Africa into the Middle East, then southern and southeast Asia, then
New Guinea and Australia, followed by Europe and Central Asia.
• Some modern day men in Sudan, Ethiopia and southern Africa are
the closest lineal descendants to the first Homo sapiens who left
Africa
• New Guinea and Australia were settled early in the process
• Japan has remained in genetic isolation. Mutations are strikingly
different from those of surrounding populations, they account by
themselves as a specific haplogroup
• Native Americans have a common ancestry with Eurasians and East
Asians
Microsatellite DNA Analysis
• Researchers tried to find the estimated
time of the deepest split of the human
population.
• Applied a genetic distance measurement
to 30 microsatelite regions to construct a
pylogenetic tree for 14 world-wid human
populations
What did they find?
• In the tree obtained, the deepest root
separated Africans from non-Africans.
• Their calculations suggest the split
ahppened an en estimated 115,000 to
156,000 years ago.
mtDNA Analysis
• Study on the complete mitochondrial
genome.
• 16,500 base pairs in each sequence
• 53 people diverse from different
geographical, racial, and linguistic
backgrounds.
Results
• A tree rooted in Africa
• Tree suggests that some Africans are
closer to Europeans and Asians than to
other Africans.
Fossils
• Archeologists find a fossil in Herto,
Ethiopia dating about 160,000 years old
• The oldest fossil found of Homo sapiens
dates back 115,000, and is found in Israel.
• Researches link the fossil found in Israel to
the fossil in Herto, Ethiopia and other
fossils found in Africa, based on physical
characteristics of the skull.
Conclusion
• DNA sequencing evidence shows that
modern humans originated in Africa and
migrated north out of African, then
eventually to the rest of the world.
• Oldest fossils of modern humans are
found in Africa dating around 160,000
years old.