Since the unicellular creature, going through the evolution of the living organisms, until the recently ones, with complex and different kind of neurons, the nervous system has had only one purpose; to receive a particular change of energy of the environment, integrate it as an stimulus, and give a particular response to it. The stimulus can only be of two different types, harmful or beneficial, and they can have variations according the species and the particular state of the living creature.

The purpose is to survive; if an stimulus means feeding as an example, the living organism will tend to get closer to it, and if the stimulus can produce damage, the organism will tend to run away or under some circumstances to attack. This is the work of the nervous system, going from simple forms of life to the more complexes.

The software integrated in the genes that conform the nervous system of the living creatures is directed to survive; the command is to maintain life, either it can be individual or as a group, even in a multicellular organism or in a community of organisms. 

Our frontal lobes that produce in us, between other functions, the capacity of reasoning and consciousness, allow us to integrate more complex responses to the stimulus, but also give us the capacity to be aware of this particular function. Our life, and the life of our offspring, are the most important objectives, unless a particular disorder can affect this evolutive function. We have to learn in our daily lives to avoid death, and the nervous system, with this software integrated, allow us to do it.

We are completely wrong if we assume that this is a human function; many species have learn with difficulties, to deal with the death for millions of years. But what is completely true is that it has been a challenge for many human cultures to deal with the death, because of this integrated software within the nervous system.

To extend the period of life has been a priority of many cultures, and science with social application, is the tangible and useful traduction of this desire; medications, immunizations and surgery, are good examples of real products of this evolutive desire, that allow many human societies to increase the expectancy and quality of life.

If this desire has been the stimulus for many humans to research between the natural laws trying to avoid or delay death, I enjoy asking my self if this same impulse was the one who generated many speculations regarding increasing the period of life and furthermore, to describe a life (or many lives) after the one that we are sure that we know?

I do believe that this inherent desire of a continuous living that we have imprint, is the source of the concepts of life after this life that many cultures have developed through thousands of years. Many cultures have even attached the social behaviour to the promise of a better life or lives.
But furthermore; we are complete sure about the useless of our body after the death, so the life after life should be as a disembodied spirit, or as another form of living creature, invaded by our same "disembodied spirit".

I strongly believe that this incapacity to deal with death because of our genetic programming, is the  origin of the soul, spirit or any kind of living energy capable to have consciousness.

We love to see to the humankind as a species particularly blessed with the feature of owning a spirit. As we eat different forms of living creatures daily, we don´t feel any particular pain because of their deaths, because they have not the spirit inside as we are sure we have. Even in our times, that we have corroborated that we are guided by the same natural laws that govern to every living creature, we tend to see us as an special one, because of the feature of own an spirit that can transcend our death.

I do believe that at the light of the current knowledge, that we should adopt a more mature and humble attitude. I do believe that we have to accept our selves as a part of the living creatures, governed by the same rules, with some particular features that make us different from other species, but with anything special, or better to others, just different. We have to see ourselves as a temporal byproduct of the genes, with defined cycles, so we can focus our efforts to improve our quality of our current and unique life, and to live in harmony with the other living species, improving the management of the resources.

We have to superimpose our knowledge to our genetic structure; it will be a painful experience, but at the end we can build better lives if we learn to accept that this one that we enjoy, is unique and perishable.