I was thinking about the origins of mankind- as we know it now, living in organized society with language, and how sefer bereshis relates to this emergence.

Animal sacrifice is clearly a very powerful cathartic method for most, if not all ancient peoples.  But why is this?

In Judaism sacrifice acts as a way to give a gift to God, and also a vessel for teshuvah.

The first place in the bible that sacrifice is mentioned is concerning Cain and Abel.  That Abel brought an animal sacrifice and God was pleased, and God was displeased with Cain's agricultural sacrifice (did not seem too upset about it though).  Cain killed Abel and mankind proceded from Cain and Seth after him.

I think that in the history of mankind from an evolutionary stand point animal domestication, and certainly hunting preceded agriculture.  This was an older lifestyle.  Animal consumption was necessary for early humans to survive because of the energy and nutrients it provides.  As mankind became more civilized living in communities, a more substantial conception of morality emerged.  With this emergence perhaps came the idea that it was 'wrong' or 'unfair' to kill animals. However at this point it was a necessary and ingrained part of life and was not going to be abandoned.  Therefore a guilt association became permanently bound with meat consumption.

Now how meat consumption became the vessel for teshuvah I have no idea, I'm sure Freud would have some insight into how a source for guilt could become the absolver.  Also not sure how the story of Cain and Abel would fit into this paradigm exactly.  I do think it makes sense though to say that Abel represented an older, antiquated lifestyle.