Charlie Wood in Quanta:
If you could shrink small enough to descend the genetic helix of any animal, plant, fungus, bacterium or virus on Earth as though it were a spiral staircase, you would always find yourself turning right — never left. It’s a universal trait in want of an explanation.
Chemists and biologists see no obvious reason why all known life prefers this structure. “Chiral” molecules exist in paired forms that mirror each other the way a right-handed glove matches a left-handed one. Essentially all known chemical reactions produce even mixtures of both. In principle, a DNA or RNA strand made from left-handed nucleotide bricks should work just as well as one made of right-handed bricks (although a chimera combining left and right subunits probably wouldn’t fare so well).
Yet life today uses just one of chemistry’s two available Lego sets. Many researchers believe the selection to be random: Those right-handed genetic strands just happened to pop up first, or in slightly greater numbers. But for more than a century, some have pondered whether biology’s innate handedness has deeper roots.