Our species the Homo sapiens dates back to 2 to 2.5 lakh years and originated in East Africa. All of us can be traced back to a single female. It is not that she was the only female at that time, there were others before her but we are taken to be the descendants of that particular female who is also called the mitochondrial eve by the scientists. But how is it possible? Scientists assume that the likeliest possibility could be the evolutionary bottleneck. It happens when majority of the populations dies, not due to lack of adoptability but due to natural catastrophe. In such case only a few survive to start the process again and that lucky female gets the honor to be the mother of all.
The initial population was very small with very limited genetic diversity. The low population and the disconnection between different groups slowly led to diversification of the genes. And again in the next thousands of years these groups again intermingled due to increase in population thereby creating a uniform genetic pool all over again.
For over a lakh years they roamed around in Africa and then started moving out towards Middle East. But then disaster struck in the form of a super volcanic eruption in Mount Toba, Sumatra about 70000 years ago. This reduced the human population to between 3000-10000 people. It will sound odd how this volcanic eruption so far away affected life so far but the eruption is estimated to be of the likes of 1.5 million Hiroshima level nuclear bomb. This had a deadly effect with about a 15 cm thick layer of volcanic ash settling over everything in South Asia and Eastern Africa. Also the sky was covered with volcanic ash blocking the sunlight bringing in winter for a decade. After this disaster the population though increased again. The population boom can be used to explain the next wave of migration out of Africa about 64 thousand years ago.
The humans stuck to the warmer climates and colonized the Middle East and the South East Asia and even up to Korea. About 60 thousand years ago humans crossed through the land bridge between Indonesia and the Asia and further went on to reach Australia. This may be the first sea faring expedition of humans to reach a completely cut off Island. Slowly these early people started to adapt to the colder regions of north and spread to these regions about 40 thousand years ago.
But the Homo sapiens were not the first to do this exodus out of Africa. There is strong evidence of humans met the Neanderthals and even interbred with them. About 1.5 to 2 percent of DNA of people of Eurasians has Neanderthal DNA in them.
The humans also took the perilous journey to reach America most likely through the inhospitable Bering Strait. Around 30000 years ago it is expected that humans from Siberia took this journey.
If we look back then 64 thousand years is not a long time. The second wave of migration to different parts started creating the first ethnic groups. This way the genetic pool diversified into various branches. We see certain diseases and traits common in certain group of people. The prominent observable difference is the skin color which is due to the melanin level of the skin. About 100000 years ago everyone was African and dark due to the tropical climate and sunshine. But the migration to different climatic areas with different levels of UV radiation and sunlight the changes in skin color started to appear. And this change took thousands of years. Scientists believe that till about 8 to 10 thousand years ago there were only black skinned people even in colder areas.
In the last 500 years with mobility of population around the world these ethnic distinctions are again blurring. Our DNA test may bring up surprising results. But this diversity has created a tortured history of mankind with battles and economic exploitation and slavery. Our ancestor, the primates like the monkeys and gorillas show hostility towards other primates within their own species due to completion for food and mates. These traits of hostility, fear, caution and aggression go back millions of years. The Homo sapiens are not much better except that we use logic and reason. We distinguish groups by physical appearance, language which was otherwise ethnically indistinguishable and this led to war and rivalries to control the resources.
In the last 150 years before scientists started understanding genetics one thing that happened is what is called scientific racism. Certain group of scientists started questioning the unified origin of humans and postulated theories that tried to justify the diversity of humans to diverse origin. Some started to describe superiority and inferiority based on such origin. The race for colonization around the world gave impetus to such views. Some even differentiated the superiority and inferiority within the Europeans and this was one of the reasons for the increase in fascism. It can also be found in the Sino-Japanese war and also the conflicts within countries in Africa like Sudan and Rwanda. If we keep ignoring our common ancestry then even today we may have consequences.
As the world is moving towards a global society, it in even more important now that we remember our common ancestry. The diversity which we see today is a totally cultural one and we should rather celebrate this diversity and not make it a reason for differentiation. And more important is the genetic diversity within us which is especially important for the survival of the human species.
Thank you Telesfor sir