This is the story of the most extraordinary journey in the history of mankind.The journey of maybe a couple of thousand Africans
across the Bab el mandeb(the tiny outlet of the red sea into the Indian ocean) fifty thousand years ago.What prompted them to leave their home in eastern Africa and set out on this journey is not certain-it could be a major climate change or rapidly declining food supplies.What is clear though is the fact that scientists all over the world have been trying to trace the movement of this tribe of Africans for decades.Their clues till now were hidden in skeletons and spearheads unearthed in various parts of the world.Genetics has provided some new clues.Clues that are slowly helping them follow the tribe on their relentless journey of colonization spanning continents.
The tools helping them unearth clues have varied through the past few decades-from DNA passed solely from mother to daughter and from father to son,to thousands of nucleotide found in bits all over the genome.Research using these tools have corroborated the fact that the first migration was from Africa and that this tribe was a storehouse of genetic diversity.
Mitochondria are unique cellular organelles which have their own DNA(albeit consisting of a meager 16,000 nucleotides)and are passed down maternally.Studies of neutral mutations (neither beneficial nor harmful) in mitochondrial DNA have shown that humans all across the world all descended from a single female in Africa-the mitochondrial Eve.Comparing the number of mitochondrial mutations between two races help us place them on a genetic family tree and trace that tree back to a common ancestor.
The male sex chromosome passed from father to son and containing a few million nucleotides was used next enabling the use of even more genetic markers.
More recently Single Nucleotide Polymorphisms(SNPs) or changes scattered troughout the genome’s three billion nucleotides began to be used as tools for tracing the genetic tree backwards.Haplotypes and copy number variations are also looked at.Similar studies on bacteria which reside in the human bbody as normal flora( for example,Helicobater pylori ) further confirmed the notions that these studies gave rise to.
The result of these analyses gave rise to some revelations and some theories.
It is now known that native South Americans have their roots in Siberia and other parts of Asia,the ethnic Han tribe of China has distinct southern and northern populations,and Bedouins are related to tribes from Pakistan,Europe and the Middle East.
The studies also gave rise to three distinct theories about the origin and migration of humns:
1: The Out of Africa hypothesis-a small group of people moved out of Africa and grew in size until a smaller group of people split from them and moved to a new destination.Every time a group split off they carried with them a bit of the original genetic diversity.With time and increasing number of splits, the diversity decreased in the newer tribes.Native Americans,one of the last tribes to migrate,have much less diversity than the Africans did.
2:The Multiregional Hypothesis-Populations originated in different locations across the globe from the older species like Homo erectus and gradually evolved as Homo sapiens.
3: This is a newer theory which has bits of both the previous theories.It explains that the first tribe came out of Africa and bred extensively with the older species like Homo erectus.A set of beneficial genes might have brought selective advantages to them.These genes were probably related to childbearing.This resulted in the resulting population resembling the original African tribe more than it was actually supposed to.