Mine are pretty full but have only gotten fuller over time. From an evolutionary standpoint, the lips are the most visible signs of sexual fitness in women. The fullness of the lips is tied to consistently high estrogen levels, which is why they're considered more attractive. There's also the theory that they resemble and remind men of vaginas, and the redder and fuller they are the more they're indicators of readiness for copulation.
Brow thickness as you all know is indicative of testosterone, but did you know that testosterone also increases the gap between the top of the lip and the bottom of the nose? Women with small gaps in that area are considered more attractive (Penelope Cruz, Julia Roberts, etc.)
[says the former cognitive science research assistant.)