What Does it Mean to Be Alive?

What Does it Mean to Be Alive?

You are on one of those trips where the travel is so tedious that even your cell phone looks boring. Not being able to sleep, you look out the window to distract yourself. You see lots of plants, people along the road, birds disappearing in the distance, and you just can’t stop wondering — how did all this life come to be? The theory of evolution explains that life adapts to its surroundings as it is selected by the environment. But how do you explain the way life itself works? How do we define the fundamental feature of life?

You could say it is the cell, but that wouldn’t help to distinguish between similar bacteria that are only one cell to begin with. How about metabolism? This is possible, except viruses aren’t able to metabolize anything without the help of another living being — the host. If you think about it, all organisms require the instructions contained in their DNA — that long twisted molecule inside the cell — to command all activities that living things do. So, what if the information coded in our genes is the underlying principle in biology, responsible for the complexity of life as we know it? Paul Davies and Sara Imari Walker of Arizona State University propose in their recent paper that information, not cells or metabolism, is the underlying principle of life.

If information is the underlying principle for the development of life, how does that information differ from the electronic information in my cell phone? On its own, the DNA can’t do anything but store the information. It is like a sentence, which does nothing until someone reads it. This is important to allow the biological system to work in a top-down manner, where all actions of the system are the result of one master control center. A skin cell can turn on a gene that produces a compound called melanin, a pigment that protects the skin from sunlight. It is because of a top-down organization that an organism can control its cells’ functions through a hierarchy of information control.

This same information flow can also be observed in biological organizations like flocks of birds, where the synchronized movement of the birds appears to have been perfectly designed. The birds communicate information to one another on how to fly and where. And just like that, information seems to play a causal role in the dynamics of biological systems, where the signals from the environment and the instructions from the genetic material act on dynamics of the individual and of the population. That certainly sounds complex!

Life forms also copy themselves, either through cell division or sexual reproduction. Life depends not only on the physical and chemical properties of the environment, but also on its own genetic material, whose instructions specify which components are to be built. And, when copying itself, the DNA molecule has the dual role of instructing which protein to build and to be blindly copied by some of those proteins, acting both as software and as hardware.

Lastly, the whole biological system is self-referential, always working through feedback loops that allow the organism to change its activity to individually adapt to the ever-changing environment. That way, organisms are always in a constant co-evolution between their physical structure and their genetic material.

The question that remains, then, is: does natural selection operate on software (information architecture) as well as on hardware (physiological architecture) of living beings? Does it happen in the same manner? It seems that there is no general agreement on how to answer those questions, but one thing is for sure: following the information may lead us to a universal principle of biology.

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