Human history and genetics

 # Science in the news

Human history, so less known

Origin of humans: Human species (Homo sapiens sapiens) evolved some 160,000-200,000 years ago from Homo erectus, from a small community in Africa continent. This modern human species may have been the cause of obliteration of it's own predecessor, i.e. Homo erectus and Homo neanderthal. This was the place in Africa from where human species spread to other parts of the world and became master today.

History books hardly tell anything about our 'most earlier ancient time'. In Indian context, they only start from 'Indus Valley Civilization' period, which was a civilization of city settlement. And traditional history says that Aryans from mid Asia invaded, destroyed IVC. There started Vedic period, Vedas as their main books, and Sanskrit-a language of Indo European group as their main language.

New tools from genetics to trace the human history:

Epic history stored in our cell

We have got our history recorded in trillions of tiny cells of the body. 
Scientists have started exploring the DNAs of the:
1. Mitochondria: as this cell organelle is being solely contributed by the mother only through the cytoplasm of her egg to her child.

2. Y Chromosome (male sex chromosome), as this chromosome is being contributed to the boys of F1 generation by the father only.

3. Haplogroups: the giant molecule of DNA is like a talismatic book. 
Mutation in longer course of time, set during cell division, growth and development of a body. 
These mutational changes in one community, may be the easy factor to co-relate the other community member for it's affinity.

The Y chromosome and speciation 

Hybridization is a natural process happening with or without human intervention. It is an important evolutionary phenomenon that helps understanding complex mechanisms such as speciation. Hybrid zones between related species are thus regarded as “natural laboratories”. So mating between genetically divergent species or populations is quite common in nature.

credit:khaled

Comparisons of introgression levels between the Y chromosome, the X chromosome, the autosomes, and mitochondrial DNA are essential to the knowledge of speciation genetics. Particularly, the important role of the sex chromosomes in reproductive isolation predicts that genetic markers found on these chromosomes will often show restricted gene flow compared to other loci.

An alternative explanation can also be suggested. Relative levels of differentiation might simply echo the rate of ancestral lineage sorting (due to differences in effective population size) which is expected to be fastest for the Y and the mitochondrial DNA, followed by the X chromosome, and finally the non-sexual chromosomes. Crossing test can be useful to assess the validity of either hypothesis.(http://www.webscienceman.com/2009/01/08/the-y-chromosome-mystery/)

The mapping of human history in terms of gene flow

Ancestral codes: Modern genetics is throwing light on our common ancestors.

Steve Olson

When a sperm fertilises an egg, the egg gets its share of the DNA in the sperm's nucleus to pair with its own. But eggs are more than just DNA - they are cells rich with enzymes, and especially the tiny particles called mitochondria, which serve as cellular energy converters.

Mitochondria also contain DNA (itself there as an evolutionary relic from some time close to the origin of life on earth) - and this we inherit only from our mothers. Analysing the variations in mitochondrial DNA from modern humans makes it possible to detect our maternal relationships.

Similar calculations can be made for the Y-chromosome that males inherit from their fathers. It is based on such analyses that it can be calculated that all modern human DNA is derived from something like 86,000 individuals, living in Africa, of whom the hypothetical Eve and Adam were the two whose lineages made it into the present day, all other lines having gone extinct.

Knowing approximately the frequency with which genetic mutations occur in mitochondrial and Y-chromosome DNA, and the number of these tiny genetic differences between one population group and another, enables one to guess when the populations diverged. These divergences can in turn be related to population movements, the great migrations which carried our many ancestors from humanity's birthplace in Africa on the long treks into Asia, Europe, Australia, and America.(http://www.theguardian.com/books/2002/jul/06/featuresreviews.guardianreview4)

link of a related topic http://sciencedoing.blogspot.in/2014/06/human-history-through-genetics.html