Historically speaking vegetarianism is the natural way of life for the human race. Vegetarian food conforms to the anatomy and physiology of the human body ideally, while a flesh diet is a carriage to develop complications in the body, in one form or the other.
  “ I have no doubt, that it is a part of destiny for the human race in its gradual development to leave off the eating of animals in the natural process, as the savage tribes have left off eating each other, when they came into contact with the more civilized.”  - the above quotation of Thoreau only reinforces our views and the findings of Dr. Allan Walker of the Maryland John Hopkins University, a further elaborate extension of the notion. Dr. Walker maintains in his works that the history of mankind on earth is as old as fifteen crore years. Out of this total of fifteen crore years, for fourteen crore ninety five lac years, mankind have lived on a vegetarian diet of fruits, nuts, roots, leaves and plants.
  The research of Dr. Walker further states the compelling circumstances under which, man had to switch over to animal food and is still continuing with it, in portions along with vegetarian food or sometimes even in Toto.
  He reveals that a massive feminine struck the earth at the end of fourteen crore ninety five lac years, since mankind came into existence; and as such, man was compelled by the nature to switch-over to animal food in order to get his daily diet requirements fulfilled. Now, a perturbing question poses itself to us, which shakes us to our roots! we are at a loss to give any explanation as to why, man has not reverted his eating habits back to total vegetarianism, whereas he is still carrying on with flesh diet, when become self - sufficient or rather more than self - sufficient of grains, vegetables, fruits, nuts, seeds and roots?
  This attitude of man is all the more confusing and difficult to comprehend, when we know that human physiology is designed to be conducive to vegetarian diet. This turning of a blind eye to the sickening offshoots of meat eating habits by the civilized world perplexes thinkers of human welfare increasingly.
Civilizations aplenty, have faced extinction and a near pre-mature demise, by the over-grazing, caused the cattle raised for meat. An erosion of the top-soil, entails eradication of civilizations. This trend of gradual downfall and decay, points its dreadful finger to an habit of meat-eating and reminds the human species, to revert back to vegetarianism and subsequently, prevent it from complications, decay of the human body system and extinction of certain species.
  Ultimately to drive home our considered views and stand, we recommend that you also consider the mind - bogging statement of a learned writer of US , John Robbins, Who says Throughout history, there have been people who have chosen to be vegetarians, because they did not feel, it was right to kill animals for food when this was not necessary and when, there was other nourishing food available.”  
  The above revelation by John Robbins brings us back to ponder on the earlier quoted lines of Thoreau, which also echoes the same thoughts.
  John Robbins in his famous book Diet for a New America further stresses - “Main cause of demise of all the great civilizations in the world has been the meat eating habits of its people.”  To further elaborate, we should consider the eating habits of mankind at the time of advent of civilization or in the stone age. Initially, man used to kill animals and eat raw meat, With the discovery of fire, they started cooking raw meat before eating. As days went by, man developed means to grow things from the earth , resulting in agricultural activities.
  Thus, with the advancement of civilization, human beings switched back to vegetarianism. Killing of animals for consumption of their meat was a barbaric act only for a span of time in-between, in the absence of alternatives. If we believe in the Darwin theory of Evolution of Mankind, we will observe that the first form of men on earth, our very first ancestors Apes and their kin, happen to be strictly vegetarians.  Adam and Eve also ate only apple fruit, initially.
  Hence, we see that the progress of civilization, brings with it the natural trends of vegetarianism. we have also witnessed that in the case of any diversion in the eating habits of mankind, specially to meat, there was no stopping to be inevitable destruction of civilizations and cultures.