The origin of life: without egg to chicken

The origin of life: without egg to chicken

Scheme according to which the first complex molecules could have been formed within a day-night cycle (Graphic: Brookhaven National Laboratory)

How simple molecules evolved into more complex variants that could self-replicate? Researchers provide a surprising new answer

The search for the origin of life is much more complicated than the search for a needle in a haystack: The researchers have to search for a needle, of which they do not know exactly what it looks like, in a haystack that existed 4 billion years ago and of which no one has taken a photo. Worse, even the exact conditions on the early earth are not known with certainty today.

For example, when did the magnetic field that protects the surface from some of the cosmic rays develop?? Nevertheless, there are a few clues, because at least the final result of the development is known. We know that DNA and RNA are the foundations of life. There was probably a time when the simpler RNA dominated the "RNA world".

But there had to be preconditions for its formation as well. The atmosphere of the earth, as much as we know, consisted of methane (CH4), ammonia (NH3), water and hydrogen. Energy was added in the form of powerful electrical discharges – and the result was an experiment by Harold Urey and Stanley Miller that was sensational in its time. In 1953, the two researchers showed that amino acids – the building blocks of life – can be formed from substances in the Earth’s atmosphere when energy is added.

The existence of amino acids is not enough yet

Only a year ago, researchers showed with the help of computer simulations that the sequence of events recreated in the Miller experiment was not only a possibility, but must necessarily have taken place in this way – provided that the circumstances were actually as is now assumed with a high degree of certainty (evolution in the primordial soup).

But the existence of amino acids is not yet enough for life to come into being. The self-duplication of life today is carried out according to a very successful and at the same time safe scheme: We have a polymer strand, which serves as a pattern for duplication. But this seems to be a chicken-and-egg problem: no pattern, no duplicate.

This was exactly the question that researchers Sergei Maslov and Alexi Tkachenko from Brookhaven National Laboratory asked themselves with the help of a computer simulation. The result has now been published in the Journal of Chemical Physics.

A compelling development

The surprising answer: In this case, too, it can be shown that the development is, to a certain extent, obligatory. The chicken definitely hatches even without an egg, and it has no other choice. The physicists show that, under certain conditions, polymers are automatically formed in a soup of simple molecules – and with them a kind of memory.

The researchers base their system on a simple day-night cycle. During the day, more complex molecules break up into smaller ones, and at night they come together again. In the simulation, a process now takes place that could very well have led to the emergence of life: The molecular strings that remain at the end of the day serve as patterns for new molecules at night, so that the length of the strings gradually increases.

Already a small amount of more complicated molecules is enough to start this process. A special molecule is not required – this kind of chemical evolution would be possible with RNA as well as with DNA (or other forms which we do not know, but which could have existed until they were wiped out by RNA and DNA life).

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