Summary - A quick random bit of introspection from the Doc's point of view on a simple concept of human life. Unbeta'd, like all my quickie-ideas.
Birthdays. He'd never quite understood the human fascination - nay, obsession, with such a vague concept. A birth-day was the date of one's arrival, in the universe. So, was it the day you were born? The day you were concieved? The day the sonogram showed others just what you would be when you left the womb?
(Jack swears he posed for THAT camera, one late night in the kitchen, while Martha points out it's not a camera. He finishes off the last of the birthday-celebration ice cream while they bicker about the differences between sonar equipment and telephoto lenses and the technological distance between the twenty-first century and the fifty-first.)
The celebration of one's birth-day is another mystery. If the date is a certain day in the calandar Earth year, but you're no longer on earth, can you claim to be one year older? If you land on the planet Seberentis P'kariana, where three solar years are the equivilent of one earth day, do you age three years by default?
(Martha comes into the Zero Room one evening while he's clearing his head, and asks how long she's traveled with him; the calander she brought with her isn't accurate anymore. He gets her a new one, one that updates automatically to Earth time. It sits forgotten on her bedstand, unopened, because she likes the feeling of timelessness.)
But the mystery deepens when his human companions try to compare his own lifespan to their rules, and it forces him to stop and think. When is his birth-day? Was it the day his genetics were picked for looming? The day the weavers stopped, and he was handed to his cousins' care? Was it the first time he regenerated? The last? Could each regeneration count as a new birth-day? And without a planet to call home, to count the days as the suns never rose and set, could he even age?
(He still lets them bake him a cake, one night, and licks frosting off his fingers, while Martha sings Happy-Birthday through a fit of giggles, and Jack hands him a gift wrapped in luminescent paper purchased from an outerworld bazzar.
That the paper is home to a colony of rather irate microscopic life forms, they'll find out later. For now, he lets them have their silly customs.)