What is the correct definition of life

Basic principles of life

What life is still cannot be defined, but it can at least be described precisely

The conference participants had spent hours discussing a catchy definition of life. Finally a catchy phrase emerged: "The ability to reproduce is the essential characteristic of life." Yeah, that sounded good. Until a low voice rang out: "Then a rabbit is dead. Two, males and females, are alive, but each one is dead."

Although everyone knows what life is - or at least believes they know it - there is currently no generally binding definition (what is life?). A deficiency that becomes more and more apparent through research on extraterrestrial and artificial life (Frankenstein's heirs). In the science magazine Science, the molecular biologist and former editor-in-chief Daniel E. Koshland, who teaches at Berkeley, has now attempted to identify seven fundamental principles of life. He calls them the after their first letters PICERAS principles.

The "P" stands for Program: Koshland understands this as a "plan that describes both the components of a living system and their interactions with one another". In earthly life this program is stored in the DNA, but there may also be other mechanisms for it.

The program must be able to adapt to changing conditions. Koshland refers to this second pillar of life as improvisation. On earth, such program changes take place in the interplay of mutation and selection.

The third pillar is Compartmentalization: According to Koshland, all living organisms are concentrated in a certain space and surrounded by a shell that closes them off from the outside world. Larger living beings, in turn, are divided into smaller units, such as cells or organs that take on special functions. These closed units are necessary in order to allow the substances necessary for life processes to react with one another in the correct quantities and concentrations.

Energy is the fourth principle of life and probably the most indisputable: life involves movement - of molecules, bodies, body parts - and movement requires energy. The earthly living beings obtain this energy almost exclusively from the sun and to a small extent from the hot interior of the earth.

Fifth, because the metabolism must inevitably lead to thermodynamic losses, life must have a system of regeneration that compensates for these losses. A heart muscle can only beat over 90 million times during a person's lifetime because it is constantly being renewed. But because this renewal process is also not perfect and aging losses occur in the long term, life can also be regenerated through reproduction.

Because living beings have to be able to adapt to sudden changes in their environment, Koshland names Adaptability as the sixth pillar of life. In contrast to the second pillar improvisation, which involves long-term adaptations through changes in the program, this adaptability is itself part of the program - a distinction that Koshland considers universal:

"In our terrestrial system, these two requirements are regulated by two different mechanisms. I believe it will be the same with any newly discovered or developed system."

The seventh and final principle of life is Seclusion. Koshland understands this to mean the ability of living systems to allow a large number of chemical reactions to take place simultaneously without interfering with one another. It is comparable to preventing short circuits by isolating electrical lines.

"The list of the seven pillars of life allows us to rethink goals and therapeutic concepts in current research."

These seven principles are necessary for a living system, but the mechanisms by which they work could be varied and, under certain circumstances, improved in a targeted manner. It is conceivable that people will replace the mechanism of natural selection with targeted changes to their life program.

"I am not recommending such a drastic change in the current mechanism of improvisation, which has served us very well over the centuries. I only point out that there is the possibility of changing certain mechanisms as long as we uphold the basic principles ourselves."

Koshland has not yet found a catchy definition for life with the PICERAS principles. But they always offer a useful basis for further research, especially on artificial life. If one day life can really be proven on other celestial bodies and studied more precisely, everything may look completely different. (Hans-Arthur Marsiske)

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