In search of a possible mechanism that could explain just how the environment might do this, McFadden’s mind turned to popular accounts he had read about quantum computing that explained how superposition could significantly speed up otherwise slow processes. With that vague thought, McFadden asked his university’s physics department if quantum processes might explain the TB adaptations. His audience did not welcome the idea. “Most of my physicist colleagues thought he was naïve, and the idea that quantum effects might play a role in adaptive mutations was ridiculous,” recalls Al-Khalili.
Yet Al-Khalili — no stranger to potentially embarrassing questions — was intrigued enough to discuss the problem. “Don’t imagine that we sat there with some grand vision that we were pioneering quantum biology,” laughs Al-Khalili. “Really we just enjoyed meeting up once a week at Starbucks to chat through things we both found fascinating.” It paid off. Over the course of a year, they hashed out a theory using quantum mechanisms to explain how adaptive mutations occur.
The Quantum Solution
DNA’s twisted ladder structure requires rungs of hydrogen bonds to hold it together; each bond is essentially made up of a single hydrogen atom that unites two molecules. This means sometimes a single atom can determine whether a gene mutates. And single atoms are vulnerable to quantum weirdness. Usually the single atom sits closer to a molecule on one side of the DNA ladder than the other. Al-Khalili and McFadden dug out a long-forgotten proposal made back in 1963 that suggested DNA mutates when this hydrogen atom tunnels, quantum-mechanically, to the “wrong” half of its rung. The pair built on this by arguing that, thanks to the property of superposition, before it is observed, the atom will simultaneously exist in both a mutated and non-mutated state — that is, it would sit on both sides of the rung at the same time.
In the case of the fast-adapting E. coli, that would correspond to its DNA being primed to both enable the bacteria to eat lactose and also not be able to eat lactose. Al-Khalili and McFadden mathematically analyzed the interactions between the single hydrogen atom in the germ’s DNA and its surrounding lactose molecules. The presence of the sugar molecules jostling the atom have the effect of “observing” it, they argue, forcing the hydrogen to snap into one position, just as measuring the state of any quantum particle will fix it to one set location. What’s more, their calculations showed that the mutation that would enable E. coli to digest lactose would occur at a faster rate than in the absence of sugar. “It was hand-waving, but we had an inkling that something quantum was happening at the level of DNA,” says Al-Khalili. He and McFadden had joined a small group of mavericks who dared to link biology and quantum physics.
Not everyone was convinced. Many of Al-Khalili’s colleagues advised him to drop this fool’s errand, arguing that no experiments had definitively shown that quantum effects play a role in biological molecules. Given the state of biological imaging at the time, verifying the pair’s theory directly seemed impossible. In the meantime, Cairns’ original E. coli study had also come under close scrutiny. The increased rate of lactose-digesting mutations was independently reproduced a number of times, says McFadden, but there were suggestions that other non-beneficial mutations might also be enhanced, too — possibly obviating the need to invoke quantum mechanics. “It was around then that we lost interest in the subject,” says McFadden. Both he and Al-Khalili forgot their lofty ambitions and returned to their day jobs.
The Work Continues
Looking back, Al-Khalili admits they were too easily swayed. In the following years, a host of experimental results sprang up hinting that quantum effects may be at work in many different corners of the biological world. The most significant appeared in 2007 and involved photosynthesis, the process by which chlorophyll molecules in plants convert water, carbon dioxide and sunlight into energy, oxygen and carbohydrates.
Photosynthesis achieves a whopping 95 percent energy transfer efficiency rate, “more efficient than any other energy transfer process known to man,” says McFadden. Within chlorophyll, so-called antenna pigments guide energy from light-collecting molecules to nearby reaction-center proteins along a choice of possible pathways. Biologists had assumed that the energy hopped from molecule to molecule along a single pathway. But calculations showed that this could account only for about a 50 percent efficiency rate. To explain the near-perfect performance of plants, biophysicists reasoned, the energy must exist in a quantum superposition state, traveling along all molecular pathways at the same time — similar to the quantum computer that could simultaneously search all entries in a database. Once the quickest road is identified, the idea goes, the system snaps out of superposition and onto this route, allowing all the energy to take the best path every time.
In the 2007 experiment, University of California, Berkeley, chemist Graham Fleming and colleagues ran experiments on green sulfur bacteria that appeared to suggest this quantum approach. Fleming’s work took place at minus 321 degrees Fahrenheit, but similar effects appeared three years later in experiments with marine algae carried out at room temperature by a team led by Gregory Scholes, a chemist at the University of Toronto in Ontario. “These were jaw-dropping experiments,” says McFadden. “Physicists had been battling for years to build a quantum computer — and now it seemed that all that time they may have been eating quantum computers for lunch, in the leaves in their salad!”
Vlatko Vedral — a physicist who whimsically describes himself as being quantum superimposed at both the University of Oxford in the U.K. and the Centre for Quantum Technologies in Singapore — took notice. “Up to then, all these ideas in quantum biology sounded good, but they lacked experimental evidence,” he recalls. “The photosynthesis experiments changed people’s minds.” Although, he adds, critics have pointed out that the tests use artificial light from lasers, rather than natural sunlight. It remains unclear whether the same quantum effects observed in tightly controlled lab conditions really do occur outdoors in our gardens.
The experiments were enough to set Vedral wondering if he and his colleagues could find quantum effects within the animal equivalent of photosynthesis. The energy factory in animal cells like our own is the mitochondrion, a repository for channeling energy from glucose harvested from food into electrons. These high-energy electrons are then shuffled through a cascade of reactions to make adenosine triphosphate (ATP), the molecule that fuels most cellular work. Conventional biological models described the electrons as hopping from molecule to molecule within mitochondria, but — once again — this simple picture cannot account for the speed at which ATP is spit out.
Vedral’s team has come up with a model in which, rather than hopping, the electrons exist in a quantum superposition, smeared out at once across all the molecules in the ATP production line. Their calculations predicted a boosted ATP production rate, as seen in experiments. Once again, it was a quantum solution to a biological mystery.
Though still tentative, the possible health ramifications of these theories have not gone unnoticed. Vedral notes that failure in electron transfer in mitochondria has been linked to Parkinson’s disease and to some cancers. The connection is still speculative, he admits, because the precise cause-and-effect relationship between the two is murky. “Does the failure of electron transfer lead to the disease, or does the disease cause the breakdown of electron transfer?” Vedral asks. “That’s something biologists don’t know, and we have to look to them for an answer.”
Nonetheless, because the payoff could be so high, the conjecture has attracted the first major research grant enabling the Oxford group, led by Oxford physicist Tristan Farrow, to run their own experiments into quantum biology. The grant stands as one of the biggest stamps of approval for this controversial discipline, which until now has largely been a topic for researchers’ spare time. As Farrow walks me around the darkened lab where these tests will take place, he explains that it’s arduous work, and it can take up to five years to prepare.