X-Selector

Flash
Replace all instances of the variable "X" in all other textboxes with Y, where Y is the amount of mana paid to cast X-Selector. (This does not affect Xs in mana costs.) (For example, if you cast X-Selector for X= 0 in response to the card Gelatinous Genesis, 0 0/0 green Ooze creature tokens would be created instead, no matter how much mana was spent to cast Genesis.)
Natural SeleXtion - {x}{x},{t}: Change the value of
Y to X.

No, it's a different X to the casting cost -