The Vital Question: Why is life the way it is? is a new book by Nick Lane that is due out on April 23rd. His question is not one for a static answer but rather one for a series of ever sharper explanations—explanations that apply at different resolutions to specific increments in the continuous chain of life, to the whole, and to generalizations of the process to other instances. For example, we might now boldly assert that an explanation for whether life evolved, or could have evolved, in the same way more than once on our own planet might also describe the same for any other planet. In reading Nick's staggeringly broad and indelible new synthesis, we reach the conclusion that in it's most rough top-level form this explanation must be that any sufficiently advanced chemiosmotic geochemistry is indistinguishable from life.

Chemiosmosis refers to the movement of ions down an electrochemical gradient and across a selectively permeable membrane. This process was there at the begining in what is now widely held to be life's most diffuse state, the alkaline hydrothermal vent. The incidentals of a chemiosmotic lifestyle have continued to exert their influence at every major subsequent induction of new form since, each time further encapsulating both the primal elements of, and various substitutions in the original geochemistry. The explanation for why all life conserves energy in the form of proton gradients across membranes contains within itself the reason why one bacterium was ultimately able to get comfortable living inside another.

As Nick details, the constraints imposed on the evolution of life by chemiosmotic coupling ultimately dictate what he calls the greatest paradox in biology: that all life on earth is divided into prokaryotes, which lack morphological complexity, and eukaryotes, which share a massive number of perplexing traits never found in bacteria or archaea, including genome-wide sex, two sexes, and ageing. The gulf between the two families, and also among individual prokaryotic domains accordingly had less to do with adaptations for unique or extreme environments and more to do with the divergence of a group whose 'membranes were obliged to remain leaky for bioenergetic reasons.'

The main idea here is that without leaky membranes, the accumulation of protons inside a cell (or on the relavent side of a vent system operating at a specific pH) would quickly lead to a buildup of positive charge that opposes the influx of more H+. In this seemingly trivial description at least, activity across primitive membranes would eventually grind to a halt. In recent times Lane and his group have taken to the computer to provide insight into some of these effects, running all kinds of simulations to vet their hypotheses. We might mention here that these same simplistic intuitions apply to ATP accumulation in mitochondria. If ATP is generated at a higher rate than it is used, respiration grinds to a halt through the action of various inhibitory feedbacks. Low ATP consumption drives higher membrane potentials to higher levels making it even harder to pump protons. The respiratory complexes therefore gradually back up with excess electrons and leak away free radicals.

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