Does Humility affect the power and toughness granted by another continuous effect applied in a later layer?

Continuous effects that modify power and toughness are all applied in Layer 7, which is subdivided into 7a (setting P/T to specific values), 7b (applying effects that set P/T, like Humility), 7c (+X/+X modifications), and 7d (switching P/T). Within the same sublayer, effects are applied in timestamp order — the most recent effect wins.

Humility sets each creature's power and toughness to 1/1 (a layer 7b effect). If another continuous effect also sets a creature's P/T to a specific value in layer 7b (e.g., a static ability or an Aura), the one with the later timestamp wins. So if Humility entered the battlefield after the other effect, Humility's 1/1 overrides it. If the other effect has a later timestamp, it overrides Humility's 1/1.

However, the dependency system (CR 613.7) can alter this. If one effect's existence or application depends on the other, the dependent effect is applied after the effect it depends on, regardless of timestamp. For example, if a lord or anthem modifies P/T in layer 7c (+X/+X), those are additive modifications applied after all 7b setting effects and so are unaffected by Humility's 1/1 reset — they still add to whatever 7b left the creature at.

Concrete example: Suppose Humility is in play (entered first), and you then put a Godhead of Awe into play (entered later, also sets all other creatures to 1/1 in 7b). Because Godhead has a later timestamp, its 1/1 effect overrides Humility's 1/1 for those creatures — but both set to 1/1 anyway, so the result is identical. Now consider a creature enchanted with Giant Strength (+4/+4, layer 7c): even with Humility in play, the creature ends up 5/5, because the +4/+4 is applied in 7c after Humility's 7b effect sets it to 1/1.

In summary: Humility competes in layer 7b by timestamp and dependency rules, and it does not override additive P/T modifications that occur in layer 7c or later sublayers. (CR 613.1, 613.3, 613.7)