Quick suggestion: Have one bike follow *exactly* the route of the previous best, with no variation, and make it obvious (colour it red and place it on a higher z-plane than the others, for example), so that we can better track how much each generation is varying from the 'best'.
Given that this is, more-or-less, just a little story told through the medium of a game, you might want to check your spelling. There are some glaring errors in there. Also, putting a low 'ceiling' surface over an area that must be jumped doesn't really make it more challenging, just more annoying. Beyond that, I would say it is a good effort :)
Super tower seems a wee bit broken. It is supposed to cost $500, and you do need to have $500 before it is available to buy, but it only actually charges you $50 when you place the tower :P