When Science is a Matter of Life and Death

Even those of us steeped in the world of science may stop in our tracks when confronted with the fact that we still don’t know what defines ‘life’. What does it mean to be ‘living’? And how simple can life get?

Viruses are a great example of particles that skirt the border of living and non-living. After the havoc they created during the pandemic, rapidly evolving new and more powerful strains, it’s incredible that there is still debate on whether they are living organisms. Many biologists now believe that viruses are not a form of life but organic structures that interact with living organisms. For an entity to qualify as living, they must be able to reproduce independently, and we know that viruses cannot. Others like virologist David Bhella believe that the only satisfactory definition of life lies in “the most critical property of genetic heredity: independent evolution… Viruses fulfil this definition.”

Entities like viruses and prions lie in this transition zone between the non-living and the living. If we move further towards the non-living end of the spectrum, we encounter the complex organic chemicals that form the precursors of life ‒ amino-acids for example. In a letter to his friend the botanist Joseph Dalton Hooker, Charles Darwin mused: “But if (and oh what a big if) we could conceive in some warm little pond with all sort of ammonia and phosphoric salts, ‒ light, heat, electricity present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present such matter would be instantly devoured, or absorbed, which would not have been the case before living creatures were formed”

Decades later, chemists Stanley Miller and Harold Urey practically recreated Darwin’s pond, and found that his scenario was remarkably astute. Their classic experiment, at the University of Chicago, proved that amino acids are indeed created when inorganic molecules swimming in a ‘primordial soup’ are exposed to electricity. This was a giant breakthrough in the study of the origin of life, or abiogenesis.

Once scientists demonstrated how the building blocks of life may have come about on earth, they moved on to the question of what next. “We assume we have the chemical building blocks of life: the question we’re looking at is what do we need to do to make these chemicals get together and work like a cell?” asks biochemist Jack Szostak. That’s precisely what his lab, situated in the University of Chicago just like Urey’s, is trying to do ‒ bring molecules to life, or as he calls it, “that transition from chemistry to biology”. In the 2000s, he had some success with this. His team was able to synthesize “protocells”, extremely simple cells that are able to assemble from the chemical precursors that were present in early Earth.

A Rocky Start

In 1969, residents of the town of Murchison in Australia observed a bright fireball hurtling through the sky and, shortly after, heard the crash. When geologists and biologists collaborated to study fragments of the Murchison meteorite, they discovered that it contained amino acids, hydrocarbons and other chemicals considered as the precursors of life. There was adequate proof that these chemicals originated extraterrestrially. Since then, there has been mounting evidence that the building blocks of life not only formed on earth, as Miller and Urey demonstrated, but also came from space via meteorites and asteroids. As NASA astronomer Scott Sandford reportedly said, “It’s a lot easier to build a house out of Legos when they’re falling from the sky”.

With the advances in space technology, scientists no longer need to wait around for meteorites to strike earth to study extraterrestrial material. In 2020, a NASA spacecraft touched down on an asteroid named Bennu, collected a sample from its surface, and dispatched this back to earth in a capsule that landed in 2023. Upon subjecting this pristine sample to analyses, the team of scientists were thrilled to discover that the asteroid’s dust was rich in carbon and nitrogen, and it also contained organic compounds such as amino acids! More recent studies on the Bennu sample have detected sugars that are essential for life “including ribose and, for the first time in an extraterrestrial source, glucose.”

Intriguingly, it seems that the amino-acids in Bennu were formed in frozen conditions ‒ very different from the “warm soup” that we believed was a critical requirement for life to evolve. And so it turns out that there may be multiple recipes to cook up the building blocks of life. Naturally, this has gotten astronomers excited about the possibility of past or present life in exoplanets, i.e. planets outside the solar system. There has been a flurry of discoveries of Earth-like planets which may have environments suitable for life. As astronomer Didier Queloz asks, “Why should Earth be a kind of strange system with life?”

Smashing Boundaries

It is no wonder that “Life” is a key theme at this year’s interdisciplinary Lindau Nobel Laureate Meeting. As the advances discussed above illustrate, it is not only biologists and chemists who are asking grand questions about what life means, how it came about, what keeps us living and why it’s got to end. When it comes to studying “life”, researchers are collaborating across disciplines, giving birth to new fields of science that blur the borders between the physical, chemical and biological sciences. And it’s hard to ignore the philosophical implications of all this work. Chemist Jean-Marie Lehn likes to challenge the dominant belief that human beings represent the most advanced evolution of life: “On other planets there may be even more complicated organisms than we are, or whatever, something more complicated.” He believes that science can “contribute to understanding how the universe has led to this very complex state and preparing the next complex state.”

The physicist Erwin Schrodinger mused on the subject of life as early as in 1944, with the publication of his book What is Life. The central question of the book was, according to him, “how can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?” He presented the notion of an “aperiodic crystal”, a physical manifestation of hereditary material, years before we knew about the double helical structure of DNA. The ideas in this book are often credited for kicking off the field of molecular biology.

For a discipline younger than a century, molecular biology has given us an overwhelming number of breakthroughs that throw light on the mechanisms that keep life ticking. Arguably, the most famous of these is the discovery of DNA’s structure by Rosalind Franklin, James Watson, Francis Crick and Maurice Wilkins. They were able to explain how hereditary information is transferred. Interestingly, all three who won a Nobel for the discovery have stated that their interest in DNA was sparked by Schrodinger’s book. “It looks as though your term ‘aperiodic crystal’ is going to be a very apt one,” they wrote in a letter to Schrodinger in 1953.

Since then, scientists have deciphered the genetic code, uncovered mechanisms by which proteins are made and broken down, and revealed how cells regulate their own death. These are all discoveries in fundamental science, but their implications go beyond knowledge gathering. We now know more about the biology of aging than at any point in history, and the prospect of manipulating these pathways has opened up tantalising possibilities while fuelling the imagination. However, most scientists studying aging stress that the point is not to discover the secret to living forever, but to understand why cells age and use science to improve and prolong the healthy, active years of life.

For all our ability to zoom out to the scale of galaxies and zoom in to the scale of molecules, it is humbling that the answer to the most fundamental question of all, i.e. “What is life?”, still eludes us. But maybe this inability is our strength. As philosopher of science Carol E. Cleland writes, “Life is not the sort of thing that can be successfully defined. In truth, a definition of life is more likely to hinder than facilitate the discovery of novel forms of life.”

This year’s meeting at Lindau will explore the theme of life in exhilarating detail. Talks and discussions by Laureates will bridge cosmology, chemistry, molecular biology, and aging research, to trace the arc of existence from the birth of galaxies to the biological rhythms that define our mortal condition.