Eric Schneider and James Kay contend

¹

that life is evolved to most efficiently execute the second law of thermodynamics to produce maximum entropy. Could biological diversity "be driven by a simple physical law? In the realm of ecology, at least, there's evidence that it is." Life will take advantage of any energy gradient, tending to reduce it to equilibrium.

"To understand why, consider what it means to be out of equilibrium. To describe the quality of energy in a system, the portion of some lump of energy that you can extract as useful work is called exergy. At equilibrium you can't extract any more work, so that the exergy is zero."

In any ecosystem there is an energy-chain from high to low, just as there is a food-chain. Humans are consumers of energy in wide variety; at each extraction point, work is done at some level of efficiency accompanied by production of lower grade energy, usually in the form of heat. All living things consume energy, the useful work being maintenance of each entity's bodily functions. Life is as diverse as there are viable energy gradients to exploit.