Shades of Gray

“What is Life?” is a difficult question to answer, perhaps because there is no clear boundary between life and non-life.

 

An alternative approach is to posit a continuum between life and non-life – shades of gray between the clear black and white cases. A month ago, a raft of sixteen co-authors published a perspective article: “The Grayness of the Origin of Life” (Smith et. al., Life 2021, 11, 498). They see this continuum in five areas of chemistry: organic molecules (biotic and abiotic), information storage systems (nucleic acids and derivatives), metal catalysts, energy-transduction molecules, and compartment-building molecules. In each case, there’s a continuum composed of different shades.

 

Their conclusion: “A grayness persists throughout biology. This is particularly true in life’s earliest transition from geochemistry to biochemistry. This grayness is associated with the degree of chemical disequilibrium. Life exists in disequilibrium from the environment and maintains this disequilibrium, using it to perform work. While the equilibrium state might be clearly abiotic, there is no inherent threshold to cross into the biological. Of these gray intermediate states, the distinction between proto-life at disequilibrium and a metastable mineral, for instance, is hard to discern.”

 

The practical outworking of this might be to come up with a question list. Does it reproduce? Is it self-sustaining? Does complexity increase? Is evolutionary change and adaptation possible? Is energy transduced? Are there cells or compartments? Clear-cut cases would check all the boxes or none of them. Shades of gray would be checking some of these boxes. Life-like might be what we call these systems or organisms. Are some of these check-boxes more important than others? I suppose there’s the rub. We might not be able to come to agreement on these, and perhaps that’s as it should be – if indeed the complex is not reducible to parts.

 

At the end of his book, Life’s Edge, Carl Zimmer posits an analogous question to make the point that such ambiguous questions are common. “What is a game?” As someone whose hobby once-upon-a-time was playing board-games and card-games, I found this an interesting question to ponder. Presumably a board-game is a game that has a board; a card-game is a game that uses cards. So those were easy to define. But what is a game? (You might also ask: what is a board? what is a card?) That’s not so easy to define. Not all games have boards or cards or counters or dice, and some may not require any “equipment”. But they do all have rules or some sort of constraint. These rules are idiosyncratic to each game. Presumably they have players that engage the game, either solo or with a crowd.

 

To play a game, you learn the rules, and if the game is interesting and engaging, there will be multiple potential outcomes and layered strategies. You won’t appreciate these without multiple plays. Is our present “game” of life one of the more engaging ones? I think so, or I wouldn’t be studying it. Are we pawns in this game? I don’t know. Can some of the rules be bent or broken? I suppose it depends on the open-endedness of the system. That’s what makes it complicated. And perhaps shades of gray is the appropriate approach to such questions. Or Venn Diagrams.