Human history started when the humans learned to write, it was more than 300 B.C, and after Cristo's death a new calendar has been writen, so whe celebrate not only a new year. Whe celebrate 1 more year of health, peace and many other good stuff that happened on ur life, and many others preffer to celebrate in a church so they can pray for their departed family members, so celebrating 1 year is much more than celebrating a new year, its like celebrating a new era and hoping for even better year.
300 BC? not true. Thats too early. Greeks like Aristotle, Plato or Socrates are older than that and yet we have a rich collection of their works. (thanks to people like Averroes - look it up on wikipedia)
The first organized writings were *probably* produced around 3500 B.C... Back then they used cuneiform script.