Thanks Ayan for helping me understand this question. As Ayan said, higher evolutions tend to giveout more Experience, and while this is 100% true, I happen to know why. The way the Exp mechanics work, if you defeat a higher level Pokemon with a lower level Pokemon, the lower level Pokemon will gain more Exp than if they were the same level, because it was alower level. If a higher level Pokemon beats a lower level Pokemon, the same thing is applied, just backwards. The higher level Pokemon would gain less Exp than normal because it was a higher level, and the fight would have been easier, meaning it wouldnt get much experience from an easy fight. Since second and third evoltion Pokemon are almost always found in the wild at higher levels than their previous evolutions, more Exp will be gained, simply because their levels are higher. This is also a good deal part to the fact that higher evolutions have higher Base EXP (Thank to No1974 for that little tidbit).
