It's my mom's birthday today (Happy Birthday Mom!) and my daughter's a week from today, so I was wondering about the tradition of celebrating the day one was born.
I wasn't able to find a whole lot of 'official' information about birthdays, but I did find this website
Part of the reason birthdays are a big deal is because sociologically, almost all cultures celebrate 'rites of passage', and the day of birth is the first 'rite'. While Jehovah's witnesses are famous for NOT celebrating birthdays (as well as other holidays like Christmas, the 4th of July etc.,), most other religious groups and cultures consider them to be an important day.
From what I can find, most research agrees that birthdays were not celebrated until society began to use calendars to mark time, as before that time, it would have been difficult to pinpoint a 'day' of birth. That seems only logical, but it's interesting to think that there was a time when cultures did not pay attention to specific days, and had no concept of days of the week or months and instead simply passed through life from season to season.
A diplomat is a man who always remembers a woman's birthday but never remembers her age
— Robert Frost.