to his “neutral theory of molecular evolution.” This is a staid name for what many scientists consider the most interesting revision of evolutionary theory since Darwin. Kimura’s discovery began with a paradox. Starting in the early 1960s, biologists could finally measure the rate of genetic change in species undergoing natural selection. As expected, the engine of evolution was random mutation: double helices suffered from a constant barrage of editing errors. Buried in this data, however, was an uncomfortable new fact: DNA changes way too much. According to Kimura’s calculations, the average genome was changing at a hundred times the rate predicted by the equations of evolution. In fact, DNA was changing so much that there was no possible way natural selection could account for all of these so-called adaptations.
But if natural selection wasn’t driving the evolution of our genes, then what was? Kimura’s answer was simple: chaos. Pure chance. The dice of mutation and the poker of genetic drift. At the level of our DNA, evolution works mostly by accident.* Your genome is a record of random mistakes.
But perhaps that randomness is confined to our DNA. The clocklike cell must restore some sense of order, right? Certainly the translation of our genome — the expression of our actual genes — is a perfectly regulated process, with no hint of disarray. How else could we function? Although molecular biology used to assume that was the case, it isn’t. Life is slipshod. Inside our cells, shards and scraps of nucleic acid and protein float around aimlessly, waiting to interact. There is no guiding hand, no guarantee of exactness.
In a 2002 Science paper entitled “Stochastic Gene Expression in a Single Cell,” Michael Elowitz of Caltech demonstrated that biological “noise” (a scientific synonym for chaos) is inherent in gene expression. Elowitz began by inserting two separate sequences of DNA stolen from fireflies into the genome of E. coli. One gene encoded a protein that made the creatures glow neon green. The other gene made the bacteria radiate red. Elowitz knew that if the two genes were expressed equally in the E. coli (as classical biological theory predicted), the color yellow would dominate (for light waves, red plus green equals yellow). That is, if life were devoid of intrinsic noise, all the bacteria would be colored by the same neon hue.
But Elowitz discovered that when the red-and green-light genes were expressed at ordinary levels, and not overexpressed, the noise in the system suddenly became visible. Some bacteria were yellow (the orderly ones), but other cells, influenced by their intrinsic disorder, glowed a deep turquoise or orange. All the variance in color was caused by an inexplicable variance in fluorescent-protein level: the two genes were not expressed equally. The simple premise underlying every molecular biology experiment — that life follows regular rules, that it transcribes its DNA faithfully and accurately — vanished in the colorful collage of prokaryotes. Although the cells were technically the same, the randomness built into their system produced a significant amount of fluorescent variation. This disparity in bacterial hue was not reducible. The noise had no single source. It was simply there, an essential part of what makes life living.
Furthermore, this messiness inherent in gene translation percolates upward, infecting and influencing all aspects of life. Fruit flies, for example, have long hairs on their bodies that serve as sensory organs. The location and density of those hairs differ between the two sides of the fly, but not in any systematic way. After all, the two sides of the fly are encoded by the same genes and have developed in the same environment. The variation in the fly is a consequence of random atomic jostling inside its cells, what biologists call “developmental noise.” (This is also why your left hand and right hand have different fingerprints.)
This same principle is even at work in our brain. Neuroscientist Fred Gage has found that retrotransposons — junk genes that randomly jump around the human genome — are present at unusually high numbers in neurons. In fact, these troublemaking scraps of DNA insert themselves into almost 80 percent of our brain cells, arbitrarily altering their genetic program. At first, Gage was befuddled by this data. The brain seemed intentionally destructive, bent on dismantling its own precise instructions. But then Gage had an epiphany. He realized that all these genetic interruptions created a population of perfectly unique minds, since each brain reacted to retrotransposons in its own way. In other words, chaos creates individuality. Gage’s new hypothesis is that all this mental anarchy is adaptive, as it allows our genes to generate minds of almost infinite diversity.
And diversity is a good thing, at least from the perspective of natural selection. As Darwin observed in On the Origin of Species, “The more diversified the descendants from any one species become in structure, constitution and habits, by so much will they be better enabled to seize on many and widely diversified places in the polity of nature.” Our psychology bears out this evolutionary logic. From the moment of conception onward, our nervous system is designed to be an unprecedented invention. Even identical twins with identical DNA have strikingly dissimilar brains. When sets of twins perform the same task in a functional MRI machine, different parts of each cortex become activated. If adult twin brains are dissected, the details of their cerebral cells are entirely unique. As Eliot wrote in the preface to Middlemarch, “the indefiniteness remains, and the limits of variation are really much wider than anyone would imagine.”
Like the discovery of neurogenesis and neural plasticity, the discovery that biology thrives on disorder is paradigm-shifting. The more science knows about life’s intricacies, about how DNA actually builds proteins and about how proteins actually build us, the less life resembles a Rolex. Chaos is everywhere. As Karl Popper once said, life is not a clock, it is a cloud. Like a cloud, life is “highly irregular, disorderly, and more or less unpredictable.” Clouds, crafted and carried by an infinity of currents, have inscrutable wills; they seethe and tumble in the air and are a little different with every moment in time. We are the same way. As has happened so many times before in the history of science, the idée fixe of deterministic order proved to be a mirage. We remain as mysteriously free as ever.
The lovely failure of every reductionist attempt at “solving life” has proved that George Eliot was right. As she famously wrote in 1856, “Art is the nearest thing to life; it is a mode of amplifying experience.” The sprawling realism of Eliot’s novels ended up discovering our reality. We are imprisoned by no genetic or social physics, for life is not at all like a machine. Each of us is free, for the most part, to live as we choose to, blessed and burdened by our own elastic nature. Although this means that human nature has no immutable laws, it also means that we can always improve ourselves, for we are works in progress. What we need now is a new view of life, one that reflects our indeterminacy. We are neither fully free nor fully determined. The world is full of constraints, but we are able to make our own way.
This is the complicated existence that Eliot believed in. Although her novels detail the impersonal forces that influence life, they are ultimately celebrations of self-determination. Eliot criticized all scientific theories that disrespected our freedom, and instead believed “that the relations of men to their neighbours may be settled by algebraic equations.” “But,” she wrote, “none of these diverging mistakes can co-exist with a real knowledge of the people.” What makes humans unique is that each of us is unique. This is why Eliot always argued that trying to define human nature was a useless endeavor, dangerously doomed to self-justification. “I refuse,” she wrote, “to adopt any formula which does not get itself clothed for me in some human figure and individual experience.” She knew that we inherit minds that let us escape our inheritance; we can always impose our will onto our biology. “I shall not be satisfied with your philosophy,” she wrote to a friend in 1875, “till you have conciliated Necessitarianism … with the practice of willing, of willing to will strongly, and so on.”
As Eliot anticipated, our freedom is built into us. At its most fundamental level, life is full of leeway, defined by a plasticity that defies every determinism. We are only chains of carbon, but we transcend our source. Evolution has given us the gift of infinite individuality. There is grandeur in this view of life.
* Newton himself wasn’t so naïve: “I