But mammals have at their disposal ten times the resources, they
Essentially all life uses redox chemistry to generate a gradient of protons across a membrane. Why on earth do we do that? 
Without programmed cell death, the bonds that bind cells in complex multicellular organisms might never have evolved.
A piece of bad news wrapped in a protein coat.
The igneo-aerial food. In other words, despite
multicellular life. All animals, all plants, all of them depend on 
Our terminal decline into old age and death stems from the fine print of the contract that we signed with our mitochondria two billion years ago. 
But whatever our beliefs, this richness of understanding should be a cause for marvel and celebration. 
One begins to wonder if all the most interesting problems in physics are now in biology. 