Geology Reference
In-Depth Information
ofthesesecond-generationvariantsbindmuchbetterthananyofthefirstgeneration.Some
of the mutant daughter strands significantly outperform their parents. Repeat the whole
process a few more times, and the resultant RNA strands get better and better at binding,
until the best mutants are perfectly functional: they lock on to their targets with the highest
possible binding energy.
Thewholeexperimenttakesafewdays—lessthanaweekfromrandomstrandstoaper-
fect binding molecule. But if you were to ask a team of the world's most brilliant chemists
to design such a functional RNA strand from scratch, they would find the task to be virtu-
ally impossible with any known computational method. No current method can predict ex-
actlyhowalongRNAstrandwillfoldup,orhowitmightattachtoothercomplexlyshaped
molecules. Molecular evolution, not intelligent design, is by far the fastest and most reli-
able path to achieving function. (That'swhywe say if Godcreated life, she'ssmart enough
to use evolution.)
Life's Explosion
In the prebiotic broth, a collection of molecules with even the slightest useful function had
anadvantage.Butthesemoleculargamesofwarpaledbesidetheadvantageconferredupon
the RNA strand that had a useful function
and
could make copies of itself. Such a self-
replicating molecule ensured its own survival by producing more or less identical daugh-
ters. What's more, the molecular copying process was inevitably messy, so some of those
RNA copies were mutants. And while most mutations were lethal or conferred no signi-
ficant advantage, a few fortuitous individuals outshone their parents, and thus the system
evolved.Simplybychancecopyingerrors,theoriginalself-replicatingmoleculemusthave
produced offspring that tolerated more extreme conditions of pressure or heat or salt, or
replicated faster, or found new sources of food, or destroyed their less fit neighbors. Even
greater advantages were enjoyed by those RNA strands that found protection on a mineral
surface or refuge within a safe, encapsulating membrane.
Without competition, the first self-replicating molecules engulfed Earth's nutrient-rich
zones in a geological instant. It's perhaps counterintuitive to think of a microscopic object
taking over, but say, just for argument, that the first relatively inefficient self-replicating
moleculetookaweektoduplicateonce.(Manymodernmicrobes,bycontrast,canreplicate
in a matter of minutes.) Week by week, two strands became four, four became eight, and
so forth. At that rate, it would have taken about half a year to form a clump of one hundred
million self-replicating molecules—an object just large enough to see with the naked eye.
In another twenty weeks, the mass of RNA would have expanded to fill a thimble. And at
this rate, it would take yet another twenty weeks for all of life's earliest manifestation to
fill a good-size bathtub.
