Published On: Tue, Jun 11th, 2019

In Search of Life’s Beginnings

It’s no secret that scientists like to argue—publishing competing theories, shouting ideas at conferences and even debating one another on Twitter. These arguments are useful for weeding out bad ideas. But every now and then, a worthwhile idea is discarded.

That’s what happened to an idea proposed almost a century ago by Soviet scientist Aleksandr Oparin about how life first formed on Earth. Now his idea is being resurrected, and arguments in favor of it are winning.

Oparin predicted that the first life forms were free-floating liquid clusters in a primordial soup of life’s building blocks: methane, ammonia and a mix of other organic substances suspended in water. He suggested these clusters spontaneously separated from their surroundings, like oil droplets in water, and grabbed building blocks as they passed by—making contact between key ingredients happen more easily inside the droplet than would happen outside. Extra contact between ingredients, he proposed, made chemical reactions possible that were necessary for life to form.

Oparin went on to perform basic chemical reactions inside test-tube droplets that would confirm his theory. His experiments showed that close proximity between ingredients inside the droplets could form a short sequence of RNA, which is one of the molecules that stores information in modern cells (similar to DNA). His idea was elegant and simple; it makes sense that crowded building blocks are more likely to interact than spread out ones, just like how people are more likely to talk on a crowded bus than when they can sit alone on an empty one.

And where cells in bacteria, plants and our bodies have membranes or cell walls that define the inside and outside of the cell, Oparin’s clusters separate from their surroundings without boundaries. The droplets are more viscous than their environment—meaning they have the thick, gooey consistency of oil while their surroundings are like water. Different textures mean that those oil-like droplets favor interacting with each other over interacting with their watery surroundings. Primitive organisms that separated from their surroundings like this needed to evolve fewer parts than modern cells with membranes—an advantageous step in the formation of life.  

Unfortunately, politics and a limited understanding of biology prevented the scientific community from embracing Oparin’s droplet ideas, no matter how elegant they were. At first, his ideas were published in Russian and didn’t get much attention outside his home country. Once they were translated, scientists around the world began to debate his work. But as he was a Soviet scientist, much of what he proposed was couched in Marxist philosophy, leading Western scientists to reject his ideas during the Cold War. And it was hard to understand how Oparin’s clusters would lead to evolution of a modern cell; parts of the droplets he used contained ingredients that aren’t present in our cells today. So, biologists forgot Oparin.

Fast-forward to 2018: two collaborating scientists, Jared Schrader of Wayne State University and Seth Childers of the University of Pittsburgh, noticed something interesting inside their favorite bacteria. The protein they were studying formed clusters inside the body of the bacteria—and they conducted experiments showing that these clusters are spontaneously separating liquid droplets like the clusters Oparin proposed as the first life forms.   

Soon after, across the world in Germany, researchers at the Max Planck Institute of Biochemistry found more clusters. They were studying a different type of bacteria that performs carbon fixation—the process of taking carbon dioxide from the atmosphere and converting it into oxygen and sugar molecules that fuel the bacteria. When these researchers mixed carbon-fixing protein parts, they were surprised by what they found. The mixture clumped together, and they found out that the clumps were liquid droplets that spontaneously separate, just like Oparin’s clusters and those that Childers and Schrader found only a few months before.

These discoveries bring Oparin’s predictions back into modern debates about the origins of life. It’s easier to envision a free-floating droplet as the ancestor of life when modern cells use droplets inside their bodies to organize important reactions.

Finding droplets inside bacterial cells is especially exciting for understanding how life began. Although the droplets researchers found in bacteria aren’t the first examples of droplets in modern cells—a Princeton scientist named Clifford Brangwynne saw them in worm cells a few years earlier— it stands to reason that those inside bacteria are closer relatives of a free-floating ancestral droplet than any in the cells of more complicated animals and plants. 

But even bacterial droplets are many steps of evolution beyond Oparin’s free-floating ancestors. To fully understand early droplets, scientists need to study a large number of droplets across a variety of species. In doing so, they hope to identify features that are shared by all modern droplets. These might be inherited from a common, free-floating ancestor. For now, finding more droplets to compare shouldn’t be too challenging: the metabolic processes leading to droplet formation are performed by many types of bacteria, all of which could form droplets for scientists to compare.

It may turn out that Oparin was right—that somehow, a century before biological evidence supported his idea, he predicted a fundamental step in the evolution of life. The scientific community of Oparin’s day had reason to question his ideas because evidence was lacking. But the political agendas of Western scientists ensured he vanished from debates about the origin of life for years. Today, with new evidence and a more tolerant political climate, Oparin has a seat at the table once again. But before the scientific community fully confirms his ideas, the debate will continue.

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Scientific American Content: Global

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In Search of Life’s Beginnings