THE ORIGIN OF LIFE

First of all a definition : what is life ?

Philosophically : A system able to assume its own destiny.

Or :

An organization whose only goal is the exploitation of natural laws for selfish purposes.

Scientifically : A self-governing system able to act on its environment in order to extract the necessary substances for its construction, its functioning, and its reproduction.

All of that is explained in more learned terms by Jacques Monod (Nobel Prize) :

According to him, three fundamental properties characterize life :

- Teleonomy
- Self-governing Morphogenesis
- Reproductive Invariance

More clearly :
Teleonomy is the ability of objects able to carry out a project for themselves (reproduction) and on their environment (artefacts). However, for Monod and many others, the fact that living objects have a project does not imply that nature itself has had one in creating them. To admit that would be anti – scientific. Monod recognizes, however modestly, that one can not prove the non-existence of a project. But does one ever know ? (maybe)

Self-governing morphogenesis is the ability of objects to organize themselves (such as crystals, for example).

Reproductive invariance is the capacity of living objects to reproduce themselves and to transmit, without error, information corresponding to their own structures.

Remark 1 : Monod’s definitions do not explain the manner in which new species (as compared to what ?) could appear.
Remark 2 : The preceding remark makes obvious that we should not confuse inherent questions on the apparition of life with those that concern evolution, the progression from simple beginnings, created by nature, to more complex structures. Evolution accounts for only the potential of life, adaptaion, and selection of innumerable species (10^9 or one billion).

Preamble, to put everyone at ease : we still do not know the solution to the problem posed by the apparition of the first living object.

Preliminary paradox :

To build something, a plan and a worker are necessary And to have a plan and a worker, it is necessary to build them

This is the well-known paradox of the egg and the chicken.

Let us try nevertheless.

For life to appear, it is necessary that an autonomous system correspond to the above- mentioned definitions, and that it contain :

- a plan of manufacture (management and reproduction)
- an energy center
- a factory of organic material production (proteins, nucleic acids , hormones etc…)

All of which is contained in a "modern"cell representing a miracle of complexity and efficiency, an incredible ingenuity. In other words, an "Enigma of perfection " according to Denton (this chapter should be read without fail).

The material of life

Life is nothing more than chemistry, even if this displeases the " pure spirits " !

A typical cell comprises ten thousand billion atoms, not a single one of which is arranged by chance.

Quid of these atoms ?

Atoms : an arrangement of neutrons, protons and electrons in variable proportions and according to very rigorous rules of quantum mechanics. The first atom created in the universe was hydrogen : 1 proton + 1 electron. All the other known natural atoms were formed in the stars from hydrogen. Stars are, therefore, the plants for the basic constituents of raw material : Carbon, Nitrogen, Oxygen, Iron, Silica, Phosphorus, Sodium……..

Molecules : each different atom created in the stars has specific properties which allow it to combine with other atoms into molecules : H2O (water), HCONH2 (formamid), HCN (cyanhydric acid), CO2 (carbon dioxide), HCOOH (formic acid), CH3COOH (acetic acid), NH3 (ammonia) ….. one finds such structures in interstellar spaces … one finds even amino acids of structures analogous to the amino acids of life.

Molecules of life : among all possible collections, we find two important families :
- amino acids
- nucleotides
These molecules display the ability to form long chains. Schematically, amino acids build the basis of the construction of proteins, while nucleotides support genetic information by generating nucleic acids (RNA and DNA).

Nucleic acids show the remarkable capability to duplicate themselves. But they can not construct organisms directly. They have circumvented this obstacle, (clever, nevertheless !) by manufacturing other smaller nucleic acids able to carry the necessary information for specialized proteins in order to begin the work of construction (one calls them RNA messengers).

Remark : by ascending in the chain of elementary beings, one arrives at viruses, which are made only of DNA and can reproduce only by injecting their genetic patrimony in a host-cell. Viruses are not exactly considered living beings. These structures are, however, a key to understanding the origin of life. But this has not yet been determined.

The first instants of life

It would have been necessary to unite, in a closed space, the following essential elements of organic molecules, accumulated in sufficient concentrations : amino acids, sugars, bases, nucleotides, metals, catalysts… The ocean of « primordial » soup does not correspond to this model.
In order for the basic constituents to associate and « create » life, it would have been essential that they be gathered inside an hydrophobic membrane. Fatty compounds, lipids, know how to do this by spontaneous organization in liposomes, microemulsions, which allow isolation from the external world. Nevertheless, to allow exchanges it would have been necessary for the liposomes to link to the hydrophilic molecules, the proteins…

A mystery again : capsules, OK, but by what fortunate chance did the capsule appear at the right place, at just the right moment ? ? ? No answer at the moment ….

So, the first living being was composed of a waterproof external membrane associated with proteins to insure exchanges with the outside. Inside the membrane we find DNA, enzymes (highly specialized structures so complex that we still do not know how to synthesize them), and stocked energy in chemical form (ATP : molecules able to provide energy by reaction with the water). This first being, a thousandth of millimeter in size, is called :

LUCA
Last Universal Cell Ancestor

It and its similar unicellular descendants were the only living beings to populate the Earth for three billion years.

Bibliography

Title Author Editor Year Kind Interest

L'Origine de la Vie Robert Shapiro Flam 86-94 Bio/chem ***
Une Histoire de la Vie Gilles Macagno Ellipses 99 Bio/Ev ***
La Légende de la Vie Albert Jacquard Flam 92-99 Bio/Ev/His *
La Vie dans la Matière Gilbert Chauvet Flam 95 Bio/Maths **
Au Cœur de la VieLa Cellule Boyce Rensberger De Boeck 99 Bio ***
La Terre est un être vivant James Lovelock Flam 79-90 Bio **
Le Hasard et la Nécessité Jacques Monod Seuil 70 Bio *
La Logique du Vivant François Jacob Gallimard 70 Bio/Ev **
Evolution Michael Denton Flam 85-92 Bio/Ev ****
L'Emancipation de la Vie Josef Reichholf Flam 92-93 Bio/Ev
La Sixième Extinction Leaky/Lewin Flam 95-97 Ev
La Vie est belle S.J. Gould Seuil 91 Ev ***
Darwin et les Grandes Enigmes de la Vie S.J. Gould Seuil 77-97 Bio/Ev **
Le Darwinisme en question Phillip E. Johnson Exergue 93-96 Ev **
Le Darwinisme ou la fin d'un mythe Rémy Chauvin Rocher 97 Bio/Ev *
L'Horloger Aveugle Richard Dawkins Laffont 86-89 Ev *
Les Origines Cosmiques de la Vie Armand Delsemme Flam 94 Bio/Chem
Théorie Neutraliste de l'Evolution Motoo Kimura Flam 94 Ev
Le Livre de la Vie S.J. Gould Seuil 93 Ev **