Controversial New Theory Suggests Life Wasn't a Fluke of Biology—It Was Physics
This actually makes sense. Then you combine survival of the fittest (in other words having some survival strategy whether that be speed, or fast propagation or in humans intelligence you see where we all have wound up here on earth today as all the species that have survived still alive here on earth. And we are now in the 6th Great extinction where even humans might go extinct this time too sort of like the dinosaurs when the asteroid hit the Gulf of Mexico 65 million years ago.
Controversial New Theory Suggests Life Wasn't a Fluke of Biology—It Was Physics
Shayla Fish for Quanta Magazine
The biophysicist Jeremy England made waves in 2013 with a new theory that cast the origin of life
as an inevitable outcome of thermodynamics. His equations suggested
that under certain conditions, groups of atoms will naturally
restructure themselves so as to burn more and more energy, facilitating
the incessant dispersal of energy and the rise of “entropy” or disorder
in the universe. England said this restructuring effect, which he calls
dissipation-driven adaptation, fosters the growth of complex structures,
including living things. The existence of life is no mystery or lucky
break, he told Quanta in 2014, but rather follows from general physical principles and “should be as unsurprising as rocks rolling downhill.”
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Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation
whose mission is to enhance public understanding of science by covering
research developments and trends in mathematics and the physical and
life sciences.
Since then, England, a 35-year-old
associate professor at the Massachusetts Institute of Technology, has
been testing aspects of his idea in computer simulations. The two most
significant of these studies were published this month—the more striking
result in the Proceedings of the National Academy of Sciences and the other in Physical Review Letters.
The outcomes of both computer experiments appear to back England’s
general thesis about dissipation-driven adaptation, though the
implications for real life remain speculative.
“This is obviously a pioneering study,” Michael Lässig, a statistical physicist and quantitative biologist at the University of Cologne in Germany, said of the PNAS paper written by England and an MIT postdoctoral fellow, Jordan Horowitz.
It’s “a case study about a given set of rules on a relatively small
system, so it’s maybe a bit early to say whether it generalizes,” Lässig
said. “But the obvious interest is to ask what this means for life.”
The
paper strips away the nitty-gritty details of cells and biology and
describes a simpler, simulated system of chemicals in which it is
nonetheless possible for exceptional structure to spontaneously
arise—the phenomenon that England sees as the driving force behind the
origin of life. “That doesn’t mean you’re guaranteed to acquire that
structure,” England explained. The dynamics of the system are too
complicated and nonlinear to predict what will happen.
The
simulation involved a soup of 25 chemicals that react with one another
in myriad ways. Energy sources in the soup’s environment facilitate or
“force” some of these chemical reactions, just as sunlight triggers the
production of ozone in the atmosphere and the chemical fuel ATP drives
processes in the cell. Starting with random initial chemical
concentrations, reaction rates and “forcing landscapes”—rules that
dictate which reactions get a boost from outside forces and by how
much—the simulated chemical reaction network evolves until it reaches
its final, steady state, or “fixed point.”
Jeremy
England, an associate professor of physics at the Massachusetts
Institute of Technology, thinks he has found the physical mechanism
underlying the origin of life.
Katherine Taylor for Quanta Magazine
Often,
the system settles into an equilibrium state, where it has a balanced
concentration of chemicals and reactions that just as often go one way
as the reverse. This tendency to equilibrate, like a cup of coffee
cooling to room temperature, is the most familiar outcome of the second
law of thermodynamics, which says that energy constantly spreads and the
entropy of the universe always increases. (The second law is true
because there are more ways for energy to be spread out among particles
than to be concentrated, so as particles move around and interact, the
odds favor their energy becoming increasingly shared.)
But
for some initial settings, the chemical reaction network in the
simulation goes in a wildly different direction: In these cases, it
evolves to fixed points far from equilibrium, where it vigorously cycles
through reactions by harvesting the maximum energy possible from the
environment. These cases “might be recognized as examples of apparent
fine-tuning” between the system and its environment, Horowitz and
England write, in which the system finds “rare states of extremal
thermodynamic forcing.”
Living creatures also
maintain steady states of extreme forcing: We are super-consumers who
burn through enormous amounts of chemical energy, degrading it and
increasing the entropy of the universe, as we power the reactions in our
cells. The simulation emulates this steady-state behavior in a simpler,
more abstract chemical system and shows that it can arise “basically
right away, without enormous wait times,” Lässig said—indicating that
such fixed points can be easily reached in practice.
Many
biophysicists think something like what England is suggesting may well
be at least part of life’s story. But whether England has identified the
most crucial step in the origin of life depends to some extent on the
question: What’s the essence of life? Opinions differ.
Form and Function
England,
a prodigy by many accounts who spent time at Harvard, Oxford, Stanford
and Princeton universities before landing on the faculty at MIT at 29,
sees the essence of living things as the exceptional arrangement of
their component atoms. “If I imagine randomly rearranging the atoms of
the bacterium—so I just take them, I label them all, I permute them in
space—I’m presumably going to get something that is garbage,” he said
earlier this month. “Most arrangements [of atomic building blocks] are
not going to be the metabolic powerhouses that a bacterium is.”
It’s
not easy for a group of atoms to unlock and burn chemical energy. To
perform this function, the atoms must be arranged in a highly unusual
form. According to England, the very existence of a form-function
relationship “implies that there’s a challenge presented by the
environment that we see the structure of the system as meeting.”
But
how and why do atoms acquire the particular form and function of a
bacterium, with its optimal configuration for consuming chemical energy?
England hypothesizes that it’s a natural outcome of thermodynamics in
far-from-equilibrium systems.
The
Nobel-Prize-winning physical chemist Ilya Prigogine pursued similar
ideas in the 1960s, but his methods were limited. Traditional
thermodynamic equations work well only for studying near-equilibrium
systems like a gas that is slowly being heated or cooled. Systems driven
by powerful external energy sources have much more complicated dynamics
and are far harder to study.
The situation changed in the late 1990s, when the physicists Gavin Crooks and Chris Jarzynski
derived “fluctuation theorems” that can be used to quantify how much
more often certain physical processes happen than reverse processes.
These theorems allow researchers to study how systems evolve—even far
from equilibrium. England’s “novel angle,” said Sara Walker,
a theoretical physicist and origins-of-life specialist at Arizona State
University, has been to apply the fluctuation theorems “to problems
relevant to the origins of life. I think he’s probably the only person
doing that in any kind of rigorous way.”
Coffee cools down because nothing is heating it up, but England’s calculations suggested
that groups of atoms that are driven by external energy sources can
behave differently: They tend to start tapping into those energy
sources, aligning and rearranging so as to better absorb the energy and
dissipate it as heat. He further showed that this statistical tendency
to dissipate energy might foster self-replication.
(As he explained it in 2014, “A great way of dissipating more is to
make more copies of yourself.”) England sees life, and its extraordinary
confluence of form and function, as the ultimate outcome of
dissipation-driven adaptation and self-replication.
However, even with the fluctuation theorems in hand, the conditions on
early Earth or inside a cell are far too complex to predict from first
principles. That’s why the ideas have to be tested in simplified,
computer-simulated environments that aim to capture the flavor of
reality.
In the Physical Review Letters
paper, England and his coauthors Tal Kachman and Jeremy Owen of MIT
simulated a system of interacting particles. They found that the system
increases its energy absorption over time by forming and breaking bonds
in order to better resonate with a driving frequency. “This is in some
sense a little bit more basic as a result” than the PNAS findings involving the chemical reaction network, England said.
We need chemical reaction networks that can get up and walk away from the environment where they originated.
Crucially,
in the latter work, he and Horowitz created a challenging environment
where special configurations would be required to tap into the available
energy sources, just as the special atomic arrangement of a bacterium
enables it to metabolize energy. In the simulated environment, external
energy sources boosted (or “forced”) certain chemical reactions in the
reaction network. The extent of this forcing depended on the
concentrations of the different chemical species. As the reactions
progressed and the concentrations evolved, the amount of forcing would
change abruptly. Such a rugged forcing landscape made it difficult for
the system “to find combinations of reactions which are capable of
extracting free energy optimally,” explained Jeremy Gunawardena, a mathematician and systems biologist at Harvard Medical School.
Yet
when the researchers let the chemical reaction networks play out in
such an environment, the networks seemed to become fine-tuned to the
landscape. A randomized set of starting points went on to achieve rare
states of vigorous chemical activity and extreme forcing four times more
often than would be expected. And when these outcomes happened, they
happened dramatically: These chemical networks ended up in the 99th
percentile in terms of how much forcing they experienced compared with
all possible outcomes. As these systems churned through reaction cycles
and dissipated energy in the process, the basic form-function
relationship that England sees as essential to life set in.
Information Processors
Experts
said an important next step for England and his collaborators would be
to scale up their chemical reaction network and to see if it still
dynamically evolves to rare fixed points of extreme forcing. They might
also try to make the simulation less abstract by basing the chemical
concentrations, reaction rates and forcing landscapes on conditions that
might have existed in tidal pools or near volcanic vents in early Earth’s primordial soup (but replicating the conditions that actually gave rise to life is guesswork). Rahul Sarpeshkar,
a professor of engineering, physics and microbiology at Dartmouth
College, said, “It would be nice to have some concrete physical
instantiation of these abstract constructs.” He hopes to see the
simulations re-created in real experiments, perhaps using biologically
relevant chemicals and energy sources such as glucose.
But even if the fine-tuned fixed points can be observed in settings that
are increasingly evocative of life and its putative beginnings, some
researchers see England’s overarching thesis as “necessary but not
sufficient” to explain life, as Walker put it, because it cannot account
for what many see as the true hallmark of biological systems: their
information-processing capacity. From simple chemotaxis (the ability of
bacteria to move toward nutrient concentrations or away from poisons) to
human communication, life-forms take in and respond to information
about their environment.
To
Walker’s mind, this distinguishes us from other systems that fall under
the umbrella of England’s dissipation-driven adaptation theory, such as
Jupiter’s Great Red Spot. “That’s a highly non-equilibrium dissipative
structure that’s existed for at least 300 years, and it’s quite
different from the non-equilibrium dissipative structures that are
existing on Earth right now that have been evolving for billions of
years,” she said. Understanding what distinguishes life, she added,
“requires some explicit notion of information that takes it beyond the
non-equilibrium dissipative structures-type process.” In her view, the
ability to respond to information is key: “We need chemical reaction
networks that can get up and walk away from the environment where they
originated.”
Gunawardena
noted that aside from the thermodynamic properties and
information-processing abilities of life-forms, they also store and pass
down genetic information about themselves to their progeny. The origin
of life, Gunawardena said, “is not just emergence of structure, it’s the
emergence of a particular kind of dynamics, which is Darwinian. It’s
the emergence of structures that reproduce. And the ability for the
properties of those objects to influence their reproductive rates. Once
you have those two conditions, you’re basically in a situation where
Darwinian evolution kicks in, and to biologists, that’s what it’s all
about.”
Eugene Shakhnovich,
a professor of chemistry and chemical biology at Harvard who supervised
England’s undergraduate research, sharply emphasized the divide between
his former student’s work and questions in biology. “He started his
scientific career in my lab and I really know how capable he is,”
Shakhnovich said, but “Jeremy’s work represents potentially interesting
exercises in non-equilibrium statistical mechanics of simple abstract
systems.” Any claims that it has to do with biology or the origins of
life, he added, are “pure and shameless speculations.”
Even if England is on the right track about the physics, biologists want more particulars—such as a theory of what the primitive “protocells” were
that evolved into the first living cells, and how the genetic code
arose. England completely agrees that his findings are mute on such
topics. “In the short term, I’m not saying this tells me a lot about
what’s going in a biological system, nor even claiming that this is
necessarily telling us where life as we know it came from,” he said.
Both questions are “a fraught mess” based on “fragmentary evidence,”
that, he said, “I am inclined to steer clear of for now.” He is rather
suggesting that in the tool kit of the first life- or proto-life-forms,
“maybe there’s more that you can get for free, and then you can optimize
it using the Darwinian mechanism.”
Sarpeshkar
seemed to see dissipation-driven adaptation as the opening act of life’s
origin story. “What Jeremy is showing is that as long as you can
harvest energy from your environment, order will spontaneously arise and
self-tune,” he said. Living things have gone on to do a lot more than
England and Horowitz’s chemical reaction network does, he noted. “But
this is about how did life first arise, perhaps—how do you get order
from nothing.”
Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation
whose mission is to enhance public understanding of science by covering
research developments and trends in mathematics and the physical and
life sciences.
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