To many, DNA represents the definitive code which governs all life.  It has been compared to a sophisticated computer program from which every aspect of an individual organism is built.

Equally it has been stated that DNA is not destiny, so there is some basic recognition that DNA is not the absolute arbiter of everything biological.

However, we find that there is still a general reluctance to reduce the prominence of DNA from our understanding of biological systems.  There's no question that it is an important central figure in development, but it is only part of the process.  From this perceived role of central control, came ideas of the "selfish gene" and even the idea that random mutations are the driving mechanism of evolution (1).  In most cases, these views are misleading and often just wrong.  

When genomes were mapped, especially the human genome, there was the anticipation that this would unlock the secrets of biology and that all manner of understanding would suddenly be available for exploitation.  To our surprise, it was discovered that the overwhelming majority of DNA didn't code for any proteins, and was relegated to the status of "junk" in the popular view.  Of course, biologists knew that it wasn't "junk", but rather that it was simply non-coding, but there were no good ideas or explanations, initially, as to the role it might play. 

In short, it was discovered that not all DNA was necessarily utilized, and that there could be considerable variability in what a coded sequence might represent, versus what was actually expressed in the organism.  It couldn't even be fully stated that anything not encoded in DNA wasn't possible.  In fact, even foreign DNA could play a role.

Enter epigenetics.  

With epigenetics, it was discovered that possessing a particular DNA sequence didn't mean that the same results would be produced, or that any results would be produced.  The biological functions were a lot more specific than that, and so identical DNA did not produce identical results.  DNA regulation was a major factor in establishing the phenotype of an organism.

In recent years, it has also become apparent that the microbiota associated with each organism, not only influenced, but sometimes played a major role in the survival, and ultimate fitness of an organism.  In many cases, the microbiota interacted with the organism's systems [such as the immune system] and "trained" or calibrated the responses.  In some instances, the bacteria were actually capable of utilizing the system to their own purposes.

We still use terms like infection and disease to create an image that life is an "us vs them" situation, instead of recognizing that these terms really reflect a variety of interactions between organisms that are not so neatly described.  Infection may not relate to the organism, but rather where the organism is located.  Disease responses may not be the result of anything an organism is doing, but rather our immune response to it [i.e. meningitis].

To an individual that is sick, such distinctions may not be particularly relevant, but if we intend to understand the dynamics of what constitutes life, then such considerations are fundamental.  Microbiota changes, may be as fundamental to natural selection, as the previously held notions of mutations.  To further complicate matters, the microbiota are also responsive to xenobiotic influences [i.e. chemicals that are foreign to an organism, such as antibiotics, toxins, etc.], which can further modify them, their behaviors, and their impact on the host organism.

As one of the final considerations to ponder in all this, is a recent article that clearly shows that the most fundamental elements of what we consider to be "identical" are anything but. 
Over the past decade, research groups from all over the world have reported similar trends: they have for instance found that cloned pigs have as much variation in the expression of certain genes as naturally bred pigs.
There is no question that DNA is a "vital" element in encoding the necessary information required by future generations, but it should be equally apparent, that DNA is only one part of the process.  However, one of the difficulties in biology is reducing any element to the status of "vital" will be both correct and incorrect at the same time.  Is the heart more vital than the brain?  

What is becoming increasingly apparent is that life's success depends on a continuous interaction of processes that keep everything viable.  Reductionism is necessary to understand specific elements of those processes, but invariably it is also a holistic approach that will help us make sense of things.  However, no matter what is discovered or understood today, there is no guarantee that these processes will look the same in the future (2).

(1) There is often a sense that random mutations are a major force in evolution, rather than recognizing it as a relatively minor force for everything except possible novel traits.  The biggest factors are genetic drift and selection.

(2) This isn't to suggest that many biological processes are not conserved in the long-term and applicable to understanding life.  The biggest issue is in the continuous evolution and selection that is experienced by the organisms themselves and how that affects the overall nature of the biosphere.  Some effects may manifest in decades while others may take millions of years.  The only thing that is assured, is that it will continuously change.