10 avatar are highly scientific representing the key evolution sequence of life on planet Earth.
Initially there was no life for billions of years after cosmos.
Even earth evolved just 5 billion years before; although by now, it has been about 14 billion years since bigbang.
Again there was no life on earth for billions of years. Life evolved quite late in history of earth say about 650 million years before that too not on land rather water.
Earlier life was not visible to eyes as it was microscopic.However fishes were one of the very first life member of water club life.
Then life initially evolved as single cell algae and later on multiple fishes evolved in sea water (near volcanoes and hot regions of sea water).Thus later comes the first MATSAYA AVTAR of Lord Hari in sea.
This was followed by second sequence of life shift from sea to land. The second Avatar comes as turtle capable of living in sea as well as land . It is very relieving to understand that turtles are the only reptiles that survived the destruction of dinosaurs. Also important to note that turtle existed before 200 million years along with the dinosaurs. People often wonder that Hindu scriptures although talk of billions year long cosmic cycles and remain ignorant of dinosaurs.This stands very important information regarding same.
The third evolutionary aspect of life on earth was arrival of hairy animals. Avatar of varaha, the wild boar or Warthog, with very few hairs represent the evolution of first mammal.
The fourth Avatar of lion the Narsimha represent the the well evolved mammals full of hairs as lion has largest mane ( tuft of hairs around face ).
Fifth Avatar of the little man Vaman represent the evolution of humans from chimpanzees then and not the bigger Gorilla or orangutans apes. The Chimpanzees like early man was called HOMINIS and developed ANTI- GRAVITY muscles supplied by L2,L3,L4,L5 lumbar spinal nerves ( left and right side ). Interestingly L4,L5 segment of spinal cord nerves have no autonomic nerve supply. This evolutionary advantage of ANTIGRAVITY muscles gave humans a great advantage of walking on the ground and also allowed feasibility of upper limbs to engage in hunting or farming rather then engaging all four limbs for walking alone.
Sixth Avatar of Parshuram represent the evolution of higher yoga cum Tantric traditions and contemporary Vedic lifestyle as Parshuram ji was a student of Dattatraya Maharaj priciple and worshipped the Bhagwati Tripura sundari where as Parshuram ji father called Rishi Attari promoted Rigveda. This was just around the end of descending Satya Yuga (11,500 BC to 6700 BC) around 6700 BC.
Seventh Avatar Ram ji Maharaj existed in start of Treta Yuga and was disciple to Parshuram ji.The descending Treta Yug extended from 6700 BC to 700 BC that is for 2400 years.Thus Ramayana happened around 6700 BC.
Eighth Avatar of Shri Krishna existed around finishing of descending Dwapar Yug ( 3100 BC to 700 BC ) say around 700 BC. Thus there was a gap of about 6000 years in events of Ramayana and Mahabharata.
The ninth Avatar of Buddha born at Kapilvastu of present Nepal existed in start of descending Kali yug (700 BC to 500 AD) that is around 480 BC to 400 BC.
The tenth Avatar of Kalki Maharaj is in ascending Dwapar yug (1700 AD to 4100 AD) similar to that of Bhagwan Swami Narayan Maharaj of Akshardham ( 1781AD to 1830 AD).