-Appreciation of human beauty is related to health and fertility. People say beauty is in the eye of the beholder, which is partly true, but on a statistical level, some traits are almost universally attractive, and even babies respond differently to what is largely considered an attractive face compared to an unattractive face. Youth, symmetry, clear skin, healthy hair, bright eyes, waist/hip ratios for women and v-shaped torsos for men, height for men, athleticism for men and also for women, absence of noticeable disease or trouble, and defined secondary sexual characteristics, are very commonly thought of as attractive and are also related to health and fertility. A child's face is beautiful in the sense that we're drawn to nurture things that are cute, like kittens and especially our own children.
-Beauty in nature is often related to survival. As a species, we love flowers and pretty colors, and sunny days in lush environments, and they're associated with living, healthy environments. People are repulsed by feces, swampy poisonous water, signs of disease in people or animals or plants, lifeless and dirty environments, etc. We're inclined to move away from ugly situations towards beautiful situations. Even beautiful wintertime scenes or deserts are typically quite alive and healthy environments.
-A subset of that last point is that humans are drawn towards open spaces. We love being on mountains, standing on open fields, sitting in clearings in forests, and other spaces where we can see for a fair distance. Some people believe this is related to the fact that when we can see further, we are more protected from predators, because a human group with weapons can pretty much only be brought down by predators if surprised, like in a jungle.
There are probably differences between visual beauty and intellectual or emotional beauty, like we may enjoy a painting of something ugly because it speaks to us in some way. Beyond a certain point, and when you start getting into the rarer exceptions, it gets complicated.