The problem of the origin of life

In a previous post titled Paul Davies, popularizer of science, I mentioned the two hard problems of modern science, so called because after several centuries trying to solve them, and although considerable progress has been made, the solution to these problems seems to recede further as we move forward, a paradigmatic case of the horizon effect, which I discussed in another post in this blog with the same title. These problems are: on the one hand, the origin of life, and on the other, the origin of free will, which is sometimes identified with the problem of consciousness, although they are not exactly the same, but are closely related. In this post, I will discuss the first problem. The next post will deal with the second.

The problem of the origin of life is not scientific. It is historical. Happened only once in the history of our planet, and is impossible to reproduce, so it is beyond the reach of experimental science. Even if we were able to create synthetic life (not to be confused with artificial life, a branch of computer science), we would not know if that method of generating life was the same as what took place shortly after the origin of the Earth.

The origin of eukaryotes

John Maynard Smith

As I have said several times in this blog, the theory of evolution is now well established. However, it is far from explaining everything. Many mysteries still remain. I listed some of them in a previous post. A book by J. Maynard Smith and E. Szathmáry, The Major Transitions in Evolution (Oxford University Press, 1995), describes them in more detail.

One of these problems refers to the changes of level that have taken place in the history of life, which I made the central idea of ​​my book The Fifth Level of Evolution. As its title implies, during evolution, things have not happened in an orderly or stable manner. At various points, there were changes of state (similar to those in physics) where evolution passed a critical point that made it possible to reach higher levels and opened up huge new fields in the configuration space. These points are the following:

Water and the origin of life

All living beings, from microbes to humans, live in water or contain water. All chemical reactions that take place inside cells are carried out in water.

Liquid water is an extraordinary compound, with strange properties. It has one of the highest specific heats of all substances. This means that when heat is added to or removed from a body of water, the temperature varies more slowly than in any other liquid. This is important for living beings, as water acts as an environmental stabilizer. Also, it is the non-metallic liquid with the highest thermal conductivity, so local temperature variations are balanced very quickly.

Most liquids contract when they solidify, but water is an exception. It has its maximum density at a temperature of 4°C. The density of ice is lower, 0.92 times lower, so ice floats on water. So, when the temperature drops, water freezes from top to bottom, while other liquids solidify from bottom to top. This also has important biological consequences. In polar seas and in fresh waters of cold regions, when the temperature drops below the freezing point, the surface layer of ice insulates the water below from the cold, so that it never freezes and the beings that live there can remain alive and active, despite the harsh environmental conditions.

Probability of the existence of extraterrestrial life

In a previous post I talked about the probability of the existence of extraterrestrial intelligence and mentioned the difficulty of its calculation, as we don’t know of any planet where they exist, apart from Earth, and to calculate the probability of an event one must know the number of favorable cases and the number of possible cases. For extraterrestrial life, we ​​don’t know either.

In another post I detailed the conditions that should be necessary if life similar to ours were to be possible on a planet similar to Earth. These conditions are many, which reduces the probability that we will find life on some extrasolar planet located in our vicinity. In fact, among the almost 10,000 planets detected so far (of which just over half have been confirmed), 65 are at a distance from their star that could be favorable for life (the Goldilocks zone), but only three of them orbit around stars similar to the Sun (of the stellar class G).

Giant Viruses

John Maynard Smith

In 1966, H.J. Muller defined living beings as follows: Any being capable of multiplying with inheritance and variation. With this definition, which prioritizes reproduction and evolution as the definition of life, viruses should be considered as living beings. Other biologists, such as John Maynard Smith, thought that this criterion was too broad. It would mean that nucleic acids are alive, since they are capable of reproducing with inheritance and variation. That is why they propose adding another criterion: A living being is capable of reproducing and metabolizing. This would exclude nucleic acids, and therefore viruses, which are nucleic acids enclosed in a protein capsule, and viroids, which are isolated nucleic acids.

The tree of life, the family tree of all species of living beings, seems to indicate that all beings formed by one or more cells descend from a single individual, the first living being, which is called LUCA (Last Universal Common Ancestor). As I said in another post, some think that perhaps LUCA was not a single individual, but a network of individuals. But where do viruses come from?

The limits of biology

The limits of biology are practical, rather than theoretical, although some biological problems are so difficult, that it seems unlikely that we’ll be ever able to solve them. Among these problems, I will select the following:

·         The origin of life. The possibility of replicating an experiment is one of the fundamental principles of scientific method, as it is applied in the experimental sciences. No discovery is considered valid until it has been confirmed by an independent team. If an experiment cannot be replicated, it is not considered scientific.

The origin of life took place only once in the history of the Earth. Obviously, it cannot be replicated. Therefore, it is not a scientific fact, but a historical fact. Historic facts are treated in a different way than scientific facts: documents are sought that confirm that the fact did happen and describe how it happened. The credibility of these documents is then estimated. In the case of the origin of life, the documents would be fossil remains, but it’s practically impossible to find them, so it’s very likely that this problem will never be solved.

Is there a tree of life?

Tree of life

Many biologists would not hesitate to answer this question in the affirmative. However, in these lines I am going to raise the possibility that the answer should be negative. Let us see why.

First of all, what is a tree? When we use this term, talking about the tree of life, we don’t mean a biological tree, i.e. a plant with a woody trunk that grows to a height of several (or many) meters. We mean a mathematical tree. But what is that?

Scientific facts, historical facts

The possibility of repeating an experiment is one of the fundamental principles of the scientific method. No discovery is considered final until it has been confirmed by an independent team or researcher. If this happens, it becomes part of the scientific heritage. It follows, therefore, that a fact can only be considered scientific if it can be reproduced.

Historical facts are treated in a very different way. Documents describing the event are sought to confirm that it actually happened. Those documents are analyzed to estimate their degree of credibility. A historical fact will be more credible as a function of the number of independent documents that tell about it. The assassination of Julius Caesar is a well-documented historical fact, but it is not scientific, as it cannot be reproduced.

The origin of life is an event that most likely happened only once in Earth's history. It is impossible to repeat it, so as to study how it happened, therefore it is not a scientific fact. It is a historical fact.

What would be the documents, in the case of the origin of life? Fossil remains. But it is practically impossible to find them. Therefore, the origin of life will most likely be an insoluble problem forever.

But what if one day we make synthetic life in the laboratory? Wouldn’t we know then how the origin of life took place? Well no, for we wouldn’t be sure that the way in which we had made synthetic life were the same as when it appeared spontaneously, a few hundred million years after the origin of the Earth.

The same post in Spanish

Thematic thread on primitive life: Previous Next

Thematic thread on synthetic and artificial life: Previous Next

Manuel Alfonseca

Synthetic life, is it possible?

Frankenstein's monster

In the previous two posts in this series we have seen that the generation of synthetic life in the laboratory is probably a process more difficult than some optimists imagine.

Let’s look at one of the latest experiments in synthetic biology: George Church and Nili Ostrov, Harvard biologists, are trying to build a strain of the bacterium Escherichia coli immune to all existing viruses. How? By changing its genetic code so that viruses do not understand it and cannot use the bacterial cellular machinery to reproduce. Since the genetic code is redundant, it is possible to replace one of the codons encoding the amino acid arginine (AGA) with another that also encodes the same amino acid (CGC), and all the genes of the bacterium would go on generating the same proteins. This would be done with several rare codons. But since viruses would continue to use the substituted codons, the bacterial cell machinery would no longer be able to understand the DNA of the virus. This part of the job is almost finished. When it is done, it would also be necessary to eliminate the transfer RNAs of the missing codons and ensure that they are not remanufactured, so that the cellular machinery can no longer use them.

Note that the work done so far is the manipulation of the data recorded in the DNA. It is equivalent to changing the information contained in the hard disk of a computer so that it stops using a certain instruction of the language of the machine, by replacing it with another equivalent instruction. We are still very far from synthetic biology in the strict sense. Will it be possible to synthesize life in the near future?

Outstanding problems in the history of life

Gregor Mendel

In a previous article I wrote about the origin of life and related problems. That is only the first of the outstanding issues regarding evolution. There are many more, for we are far from having an explanation for everything that happened during the history of life.

The theory of evolution through natural selection was first proposed by Darwin and refined by his followers when new discovered biological phenomena solved some of the problems posed since the beginning of the theory:

1.      The laws of heredity (Mendel, 1865).

2.      Mutations (Hugo de Vries, 1900).

3.      The laws of genetics (Thomas Hunt Morgan, early twentieth century).

4.      The synthetic theory of evolution (Simpson, Dobzhansky and others, around 1930)

5.      The transmission of inheritance through DNA (Oswald Avery, 1944).

6.      The structure of DNA and the deciphering of the genetic code (Watson, Crick, Rosalind Franklin and others).

7.      The neutral theory of evolution (Motoo Kimura, 1968).

8.      Punctuated equilibrium (Stephen Jay Gould, 1972).

9.      Epigenetics (early twenty first century).

Rosalind Franklin