Dear Piyush ji,
Sai Ram. Thanks for bringing up a question that is very relevant not only today but has been relevant from the time the universe came into existence and will continue to remain relevant till the universe lasts. Whether you go from the spirituality route or the scientific route, the picture is clear and is consistent in the main points, and differs only in details. Let me share both the views.
If you read our Vedas, Upanishads and Puranas, you will find that the creation started from almost nothing (From the Mahapralaya) and in the beginning as the creation progressed, there was not much noticeable diversity, but the diversity went on increasing leading to the complexity of today, which is expected to increase for many more millenia before the next cataclysms catch up and start reducing the diversity and bring the Pralaya again. Sai Ram.
The scientific theory also is remarkably similar. The Big Bang theory, which is well respected, postulates that all the known universe (and much more which is not seen but is postulated to exist) has originated from a point sized singularity! As the universe went on expanding, the cooling resulted in localised clumping, the clumps became further subdivided and became galaxies, stars, planets, satellites etc., and as the cooling progressed, the primordial soup was rich in organic nutrients and some where life started and as life became more complex, the diversity has increased. The entropy of the universe is also going up and some day the universe will reverse the expanison and the Big Crunch will take place and all the known universe will collapse into a point sized singularity where space and time also vanish!
At a more modest scale, observe the growth of a fertilised egg in a womb. Initially the cells keep on dividing unformly but later on specialised structures such as bones, blood, muscles, heart etc., start developing. It is as if the building blocks remain the same but the structures differ. Is that not what is happening in society also today?
It is said that the macrocosm (the external universe) is but a reflection of the microcosm (the internal universe). And the mind of the modern man is today so complex and outward driven that the forest is not seen because it is so vast and you can see only the trees! Simlarly, each social group is seeing the differences more than the underlying unity. Sai Ram.
An example of today's divisive thinking is that people see the islands as separate land masses divided by sea but fail to see the underlying continuity of the land! Similarly, we are seeing the differences of size, shape, color, caste and creed and are forgetting the underlying unity of not only the human race but all creation. After all, all creation is made of matter and matter is just a condensed state of energy! Similarly the universal consciousness is One but appears as many.
Why this state of affairs? Again our scriptures provide the answer. Kali Yug. It is like a pendulum swinging between unity and diversity, just as the universe is oscillating. There are sub-cycles within cycles. This is one such.
Science and spirituality have a lot in common and education will help the individual, 'remember' - yes, re-member, i.e. realise his / her role as a building unit of the structure. So, while preserving one's habits, customs and culture, one also tolerates all others. Sai's philosophy is that only.
Pl. feel free to continue this dialogue. Sai Ram.
My spiritual background thanks to the grace of Sadguru Sai.