“Complexity reduces itself”

When the Earth was formed about 4.6 billion years ago, it was still uninhabited. Only with time did the first life forms emerge from the so-called primordial soup – a mixture of water and randomly distributed atoms and molecules. However, it is not yet clear how exactly this process took place. In an interview with Welt der Physik, biophysicist Dieter Braun of the Ludwig Maximilians University in Munich reports how this question can be investigated with new experiments that combine physics, chemistry and biology.

The world of physics: You investigate the origin of life. What questions exactly are you dealing with?

Portrait of scientist Dieter Braun

Dieter Braun: The great mystery is that the origin of life seems so incredibly improbable. If you look at how complex even the simplest life forms are—that is, how much genetic information is contained in, for example, algae and protozoa—then these life forms cannot simply arise from a primordial soup. So, either it’s a huge coincidence that life originated on Earth – we may even be alone in the universe. Or we don’t yet understand the early processes that make the origin of life much more likely than previously thought.

What might such processes look like?

In any case, these must be abiotic processes, which means that these processes must be free of biological molecules and proteins. Because they are created only by living things. However, what did exist in the primordial soup were certain organic molecules such as amino acids or nucleotides – the building blocks of DNA and RNA. We and other research groups are investigating such molecules. We want to find out how these simple organic molecules combine to form more complex ones. If these connections could somehow perform processes such as selection, mutation, and even replication, then a possible way for life to evolve from non-living would be revealed.

Multi-rail machine

How to implement it experimentally?

We allowed certain oligomers – molecules made up of several identical or similar units – to react with each other. We are particularly interested in molecules composed of twelve nucleotides – so-called dodecamers. However, we do not use all four naturally occurring nucleotides, but initially only two. In our experiments, we pour a mixture of such nucleotide oligomers into a reaction vessel, which is repeatedly heated and cooled, causing the molecules to bind to each other. In order to speed up these long-term processes, which in nature lasted for millions of years, we also use a biological catalyst. Although this did not exist in ancient times, it does not change the results, it just speeds up the chemical processes.

And how do the oligomers react to each other?

We found interesting patterns during the analysis. A surprisingly large proportion of oligomers linked together to form long-chain molecules. On the other hand, those dodecamers whose start and end match are stuck to themselves and are eliminated from the reaction structure. In long-chain oligomers, on the other hand, we noticed that in some places they mostly have a certain nucleotide, while in other places patterns are formed in which these two nucleotides alternate – like in a zebra.

What does this result say about the origin of life?

It is important that even with such simple physico-chemical processes, the complexity automatically decreases and certain structures appear. Special oligomers are pre-selected, so to speak. This makes it much more likely that other selection mechanisms will come into play at some point—until a point is reached where such molecules can replicate and mutate. There is still a long way to go until then. But experiments like ours show ways to reduce the gigantic complexity of the primordial soup—and with it the gigantic improbability that the first life forms could have arisen from this mixture of molecules.

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