Does Alter Self remove a creature's existing abilities?

Question

Alter Self allows the caster to assume the form of a small or medium, humanoid-type creature. It explicitly states that it's even adding corresponding abilities:

If the form you assume has any of the following abilities, you gain the listed ability: darkvision 60 feet, low-light vision, scent, and swim 30 feet.

This makes me wonder whether, even though it's not exlicitly mentioned, it will also take abilities away that the casting creature already has - in other words, if the casting creature is a Dwarf (which by default has 60ft darkvision) and turns itself into a human, does it lose darkvision?

Is there any other kind of ability that is taken away by it without being explicitly mentioned by the spell? I'm thinking primarily of racial traits such as the Catfolk's Sprinter ability (10-foot racial bonus to their speed under certain conditions), which seem to make no more sense after altering oneself.

Answer 1

Alter Self is from the Transmutation (Polymorph) magic school, as such, you lose all extraordinary and supernatural abilities that depend on your form:

While under the effects of a polymorph spell, you lose all extraordinary and supernatural abilities that depend on your original form (such as keen senses, scent, and darkvision), as well as any natural attacks and movement types possessed by your original form. You also lose any class features that depend upon form, but those that allow you to add features (such as sorcerers that can grow claws) still function. While most of these should be obvious, the GM is the final arbiter of what abilities depend on form and are lost when a new form is assumed. Your new form might restore a number of these abilities if they are possessed by the new form.

About Sprinter racial trait, I would say it is also lost if you change shape to be of another race, since it grants a racial bonus to your movement speed.

Movement Racial Traits

Sprinter: Catfolk gain a 10-foot racial bonus to their speed when using the charge, run, or withdraw actions.

A racial bonus comes from the culture a particular creature was brought up in or because of innate characteristics of that type of creature. If a creature’s race changes (for instance, if it dies and is reincarnated), it loses all racial bonuses it had in its previous form.