Why do kids climb?!?!?!

Got home from work tonight to hear Peter shouting "I'm here mummy" as i turned the corner in the hall, this is how i found him. On top of a 3 foot high box with a plasma screen t.v in it!!!!!!!!!!!!!!!!!!!!!
(Granted, a broken plasma) It was the bedroom t.v that broke this time folks, but had the replacement delivered, phhhewww!
Anyway Peter told me this is his new bed, lol, I told him it wouldnt be very nice to sleep there and he replied "no mummy, see me sleep!"
Why do little boys climb???????