Most? You mean evolutions of pre-existing Pokemon, right? Eh.. no... not even half of them are evolutions.
Azurill was the only one in 3rd gen that was related to pre-existing Pokemon.
4th gen has Ambipom, Mismagius, Honchkrow, Bonsly, Mime Jr., Happiny, Munchlax, Mantyke, Weavile, Magnezone, Lickilicky, Rhyperior, Tangrowth, Electrivire, Magmortar, Togekiss, Yanmega,
Leafeon, Glaceon, Gliscor, Mamoswine, and Porygon-Z as new stages of evolution for 1st and 2nd gen Pokemon. Chingling, Gallade, Probopass, Dusknoir, and Frosslass are also included as new stages to 3rd gen Pokemon.
It does appear to be a lot. 3rd and 4th gen cover numers 252-493. 4th gen is 387-493, which is still 106 new Pokemon, and 27 of those are new stages to pre-existing Pokemon. Not quite, but right around one-fifth.