Have you ever thought about your first ancestor from where your all the generation has evolved. We generally know about our grand-grandparent. But very few goes beyond that. What if we go back long enough to actually discover our first ancestor? That would be whole of a pleasing discovery. However, what if all the people around you also starts there journey to discover the numero uno ancestor and they all ends up with the same person like yours ?

Common descent is the scientific theory that all living organisms on Earth descended from a common ancestor. Although evolution had been suggested as far back as Ancient Greece; the first proponent of common descent appears to have been Erasmus Darwin, the grandfather of Charles Darwin, back in 1796 .

When you draw your genealogy, you make two lines from yourself back to each of your parents. Then you have to draw two lines for each of them, back to your four grandparents.Each generation back, we multiply the number by two. This leads to what is called an exponential increase: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 and so on. Hence, then eight great-grandparents, sixteen great-great-grandparents, and so on. But not so on for very long. If you go back to the time of forty generations or so, you should get to a generation of a trillion ancestors. That's far more than the total population of the world, forty generation back. This is known as genealogical paradox. The only way out of this paradox is to assume that our ancestors are not independent of one another. Actually, Many of these ancestors are duplicates; the same person can be found through multiple routes in the family tree. As the family tree grows beyond a generation (say 40-50 generation back) more and more overlapping of ancestors start to take place. That is, if you trace their ancestry back, eventually, you loop back to a common ancestor.

Let's Imagine the simplest case of a population of a constant size. For an example say a million. If people in this population meet and breed at random, it turns out that you only need to go back an average of 20 generations before you find an individual who is a common ancestor of everyone in the population. If you go back on average 1.77 times further again (35 generations) everyone in the population will have exactly the same set of common ancestors (although they will be related, of course, through different routes in all the different family trees).

In fact about 80% of the people at that time in the past will be the ancestors of everyone in the present. The remaining 20% are those who have had no children, or whose children have had no children, and so on - in other words, people who were genetic dead-ends.

How far do we have to go back to find the most recent common ancestor of all humans alive today? Again, estimates are remarkably short. Even taking account of distant isolation and local inbreeding, the quoted figures are 100 or so generations in the past: a mere 3,000 years ago. And one can, of course, project this model into the future, too. The maths tells us that in 3,000 years someone alive today will be the common ancestor of all humanity. A few thousand years after that, 80% of us (those who leave children who in turn leave children, and so on) will be ancestors of all humanity. What an inheritance!