Life requires contrast to emerge. The earliest components of life on Earth seem to have been formed as sulfur-metal compounds in the heat and pressure of hydrothermal vents. These wouldn't have done anything much, had they not been launched out through the vents and onto the seabed, where the cooler temperatures and minerals allowed organic complexes to arrange themselves. If not for that contrast of temperatures and available chemical elements, cell components would likely not have arisen.
Maintaining life also requires a balance of opposing forces. A long time later, early life (plant-like) started consuming the CO2 that filled the early atmosphere, and created a ton of useless Oxygen as a waste product... but as CO2 levels and their population dwindled, new lifeforms (animal-like) started seizing the growing abundance of O2, using it for energy production instead. Though they operate on different metabolic pathways, and food for one is garbage for the other, Plants and Animals require this contrast of chemicals and metabolic pathways to support one another's continued existence. Without it, both would die off.
Ecologically speaking, life thrives on beaches where ocean and land meet, near the treeline where forests and grasslands meet, in the space where dark caves connect to the surface world, and so on. Most critters that live primarily on one of those sides requires something that the other area has to survive. Seabed plants need soil and water from the silt below, and light from above (which too much water blocks). Predatory birds take advantage of flight to hide in tall trees for shelter, but use the speed and range of vision flight gives them to track and hunt animals in wide-open grasslands... but flying through the woods at high speed is a very dangerous and meandering affair at best, and if they fly above it the canopy makes their airborne visibility useless.
Even more abstract concepts rely on contrast, like the human mind itself. We understand the world around us in terms of contrast, by comparing new experiences to past experiences, and seeing how they differ. Say you introduce a girl to a small Dog for the first time, and teach her the word. Her brain will look at this "Dog," and maybe categorize it as a thing that has 4 legs, short fur, pointy ears, and a tail. Then, when you introduce that girl to a Cat and ask her what it is, she might say "Dog" again... after all, it too has 4 legs, pointy ears, short fur, and a tail. You and she might go through what makes Cats different than Dogs then; they have softer fur, more flexible tails, claws they can hide, etc. Eventually, when she encounters a hairless Sphynx Cat on her own when she's older, she'll have enough contrasting ideas to decide whether it's a Dog or Cat, or maybe something else entirely. Without these contrasting characteristics to compare, relative to one another, this kind of intelligent reasoning is impossible.
I think this concept even applies to things beyond life as well... order and entropy, and opposing forces seem to be a pretty common trend just about everywhere. I'll have to mull on this part some more, though.