Out-of-Africa Theory:Out-of-Africa Theory:The Origin Of Modern The Origin Of Modern

HumansHumans

Presented ByPresented By

Adrian PadillaAdrian Padilla

Background InformationBackground Information

• First species of Homo, Homo habilis, First species of Homo, Homo habilis, evolved in Africa around 2 million years evolved in Africa around 2 million years ago.ago.

• Later, a descendant of Homo habilis, Later, a descendant of Homo habilis, Homo erectus evolved (along with other Homo erectus evolved (along with other hominids), and spread out of Africa.hominids), and spread out of Africa.

• Homo erectus gave rise to Homo Homo erectus gave rise to Homo sapiens around 100,000 to 200,000 sapiens around 100,000 to 200,000 years ago.years ago.

Two Main TheoriesTwo Main Theories

• Out of Africa Theory (OOA)Out of Africa Theory (OOA) – suggests that – suggests that Homo erectus evolved into Homo sapiens in Homo erectus evolved into Homo sapiens in Africa, and then ventured out of Africa and Africa, and then ventured out of Africa and dispersed to all around the world.dispersed to all around the world.

• Multi-regional Evolution Theory Multi-regional Evolution Theory – – suggests that Homo erectus ventured out of suggests that Homo erectus ventured out of Africa and then evolved into modern man in Africa and then evolved into modern man in several different locations through out the several different locations through out the world.world.

Genetic Tools to Find the Genetic Tools to Find the AnswerAnswer

• Fossil recordsFossil records

• DNA sequencingDNA sequencing– Mitochondrial DNA analysis (mtDNA)Mitochondrial DNA analysis (mtDNA)

• Maternally inherited, therefore telling the story from Maternally inherited, therefore telling the story from the female side of human history the female side of human history

– Y Chromosome analysisY Chromosome analysis• Inherited down the paternal line, complementing the Inherited down the paternal line, complementing the

mtDNAmtDNA

– Microsatellite DNA analysisMicrosatellite DNA analysis• Segments of tandemly repeated DNA with a short Segments of tandemly repeated DNA with a short

repeat length, usually 2-5 nucleotidesrepeat length, usually 2-5 nucleotides

PolymorphismsPolymorphisms

• Polymorphism - Existence of a gene Polymorphism - Existence of a gene in several allelic forms.in several allelic forms.

• Polymorphic regions provide a very Polymorphic regions provide a very unique set of genetic markers for unique set of genetic markers for studying human origin and migratory studying human origin and migratory patterns.patterns.

• Used to construct a global Used to construct a global evolutionary tree of modern man evolutionary tree of modern man

Mitochondrial DNAMitochondrial DNA

• Out-of-Africa hypothesis was first Out-of-Africa hypothesis was first sketched out in 1987, based on sketched out in 1987, based on mitochondrial DNA analysismitochondrial DNA analysis

• Suggested that modern man first Suggested that modern man first appeared on the scene in eastern appeared on the scene in eastern Africa about 150,000 years ago, and Africa about 150,000 years ago, and left between 35,000 and 89,000 years left between 35,000 and 89,000 years ago, eventually conquering the globe.ago, eventually conquering the globe.

Y Chromosomal DNA StudyY Chromosomal DNA Study

• Researchers looked at DNA samples Researchers looked at DNA samples from 12,000 male Y chromosomes in from 12,000 male Y chromosomes in Asia.Asia.

• Looking for 3 specific mutations on Looking for 3 specific mutations on the Y chromosome known to have the Y chromosome known to have originated in Africa. originated in Africa.

• Researches found that every one of Researches found that every one of the 12,000 samples carried one of the 12,000 samples carried one of the three mutations or polymorphismthe three mutations or polymorphism

Conclusion to the Y Conclusion to the Y Chromosome StudyChromosome Study

• Little or no interbreeding of Homo erectus Little or no interbreeding of Homo erectus and Homo sapiens.and Homo sapiens.

• Individuals are descendants from AfricaIndividuals are descendants from Africa• Likely that the early African man Likely that the early African man

emigrated to North Africa and made the emigrated to North Africa and made the leap to Asia and then to the rest of the leap to Asia and then to the rest of the world.world.

• Indicates that modern humans of African Indicates that modern humans of African origin completely replaced earlier origin completely replaced earlier populations in East Asia.populations in East Asia.

More Y Chromosomal More Y Chromosomal StudiesStudies• Samples were taken from men in 22 Samples were taken from men in 22

different geographical areas. different geographical areas. – In countries that included Pakistan and India, In countries that included Pakistan and India,

Cambodia and Laos, Australia and New Guinea, Cambodia and Laos, Australia and New Guinea, America, Mali, Sudan, Ethiopia and Japan.America, Mali, Sudan, Ethiopia and Japan.

• Researchers identified 167 polymorphic Researchers identified 167 polymorphic markers on the Y chromosome.markers on the Y chromosome.

• Markers were then assembled into 10 Markers were then assembled into 10 types, called haplogroups.types, called haplogroups.

Findings from Y Chromosomal Findings from Y Chromosomal AnalysisAnalysis• Assembled a phylogenetic tree showing a migration from eastern Assembled a phylogenetic tree showing a migration from eastern

Africa into the Middle East, then southern and southeast Asia, Africa into the Middle East, then southern and southeast Asia, then New Guinea and Australia, followed by Europe and Central then New Guinea and Australia, followed by Europe and Central Asia.Asia.

• Some modern day men in Sudan, Ethiopia and southern Africa Some modern day men in Sudan, Ethiopia and southern Africa are the closest lineal descendants to the first Homo sapiens who are the closest lineal descendants to the first Homo sapiens who left Africaleft Africa

• New Guinea and Australia were settled early in the processNew Guinea and Australia were settled early in the process

• Japan has remained in genetic isolation. Mutations are strikingly Japan has remained in genetic isolation. Mutations are strikingly different from those of surrounding populations, they account by different from those of surrounding populations, they account by themselves as a specific haplogroupthemselves as a specific haplogroup

• Native Americans have a common ancestry with Eurasians and Native Americans have a common ancestry with Eurasians and East AsiansEast Asians

Microsatellite DNA Analysis Microsatellite DNA Analysis

• Researchers tried to find the Researchers tried to find the estimated time of the deepest split of estimated time of the deepest split of the human population.the human population.

• Applied a genetic distance Applied a genetic distance measurement to 30 microsatelite measurement to 30 microsatelite regions to construct a pylogenetic regions to construct a pylogenetic tree for 14 world-wid human tree for 14 world-wid human populationspopulations

What did they find?What did they find?

• In the tree obtained, the deepest root In the tree obtained, the deepest root separated Africans from non-separated Africans from non-Africans.Africans.

• Their calculations suggest the split Their calculations suggest the split ahppened an en estimated 115,000 ahppened an en estimated 115,000 to 156,000 years ago.to 156,000 years ago.

mtDNA Analysis mtDNA Analysis

• Study on the complete mitochondrial Study on the complete mitochondrial genome.genome.

• 16,500 base pairs in each sequence16,500 base pairs in each sequence

• 53 people diverse from different 53 people diverse from different geographical, racial, and linguistic geographical, racial, and linguistic backgrounds.backgrounds.

ResultsResults

• A tree rooted in AfricaA tree rooted in Africa

• Tree suggests that some Africans are Tree suggests that some Africans are closer to Europeans and Asians than closer to Europeans and Asians than to other Africans.to other Africans.

FossilsFossils

• Archeologists find a fossil in Herto, Archeologists find a fossil in Herto, Ethiopia dating about 160,000 years oldEthiopia dating about 160,000 years old

• The oldest fossil found of Homo sapiens The oldest fossil found of Homo sapiens dates back 115,000, and is found in dates back 115,000, and is found in Israel.Israel.

• Researches link the fossil found in Israel Researches link the fossil found in Israel to the fossil in Herto, Ethiopia and other to the fossil in Herto, Ethiopia and other fossils found in Africa, based on fossils found in Africa, based on physical characteristics of the skull.physical characteristics of the skull.

ConclusionConclusion

• DNA sequencing evidence shows that DNA sequencing evidence shows that modern humans originated in Africa modern humans originated in Africa and migrated north out of African, and migrated north out of African, then eventually to the rest of the then eventually to the rest of the world.world.

• Oldest fossils of modern humans are Oldest fossils of modern humans are found in Africa dating around 160,000 found in Africa dating around 160,000 years old.years old.