why do we...?

okay, this is filling in for jane's topic:
i'm sure i've mentioned the half-marathon a few times. i ran it last weekend in tucson, and didn't do so badly, if i do say so myself. i hadn't trained enough though(read: had barely trained at all) so my muscles paid for the run all this week. and yet, i'm already excited about the next run. "Next?!?!? i catch myself asking,'what the hell is wrong with you?!?"
which brings me to this week's topic: hobbies. why do we (personally or humanity as a whole) do all those weird things that have no practical value? stamp collecting? genealogcal research? playing musical instruments when one isn't any good? watching/following professional sports... what's the motivation?
sure, some things are for therapy or entertainment.
i guess i'm asking:
1)what are your hobbies/why? and
2)what reasons do you think there are for hobbies to exist as part of the human experience/what actual purpose does the practice of a hobby serve?

i've already mentioned running, which i forsee becoming more of a hobby than it has been. i'm excited to train this time instead of dreading it - look for me in the san diego rock 'n' roll marathon next june if i don't get some kind of an injury before then...
then there's the writing. i've yet to gain any money/fame/what have you from the writing, and if i'm depressed/angry and i write about it i generally get more frustrated, so i don't see a physical or mental benefit, but i continue to scribble or type random snippets, poems, short prose, chunks of historical fiction novels, etc. i have no clue why i so often want to put things on paper/screen.
i also like baking. this has a benefit: i get to eat yummy stuff. i could, however, purchase very nearly as yummy and significantly cheaper goodies at the dollar store. since i'm fairly poor, that might be a more reasonable option, but i don't take advantage of it. i stand on the hard floor until my legs and feet ache stir and knead until my hands hurt, burn myself pretty often, risk knife cuts, and get dry skin on my hands from washing/drying so often. then sometimes whatever i'm making doesn't turn out and i waste everything. there might be some instinctive domestic urges involved in this hobby, since my ancestors have been "happy" homemakers for pretty much all of recorded history. i like to think that i choose to bake though - maybe so i can share the goodies and feel important when people like them...?
last hobby to mention is that i voluntarily go clean up animal poop on a regular basis. sure, there's some fun stuff connected with that: i get to interact and play with most of the animals, and i get to spend time outdoors using the muscles that would atrophy with my desk job (if i hadn't just taken up running). the fact is though, that most of the time i spend working at the wildlife center is scooping poop and other debris up from enclosures and putting it in a dumpster. this one, i know why i do it. humans create false environments and put animals in them. now the animals don't know how to survive in their natural habitats and are past the age where they could learn how, so they have to remain in captivity. since humans created the problem, it's up to humans to take care of it. i'm a human. thus i feel a sense of responsiblity to help out however i can - especially when i see how it hurts the animals to be captive: they'll get frustrated and pace around their enclosure when i know if they were free they'd be running miles on end just because they could. then i really don't like people. i could go on for hours about how much it bugs me when people don't take responsibility for their actions, but hey, this is about hobbies. so i clean up poop, refill food and water dishes, hand out snacks, and give whatever kind of attention each animal seems to want (sometimes i get it wrong and get beat up). in return - they look forward to seeing me. there is nothing in the world like a cougar recognizing your car and running to fence to greet you, or like a wild fox finally (after 4 years) letting me touch her and feel that stunningly gorgeous fur. i know most people don't have the opportunity to interact with cougars, but so many people keep domestic pets - why?

there are my hobbies, how about yours?
ready, set, go!