Dear Marcel,

Artificial is any abstract or concrete entity that is produced by human beings on basis of a naturally occurring model. Here if you consider a 'stimulus'  that is naturally occurring, except in the present situation where human beings have induced that stimulus; it would obviously be artificial. Its result will also be artificial as it would not have occurred, except for human intervention into the natural course.  

Thanks for asking this question, Marcel. Of course, humans and all we do, think, and say are part of nature. Everything is natural. The concept of the "supernatural" just reflects one's lack of comprehension of some aspect of nature. The concept of "artificial" may be of some use, though, if defined in some other way, rather than in binary opposition to "natural."

Dear Marcel,

Digestion is a natural process. If human beings make a machine that digests  outside the body it will produce artificially digested carrot. An amusing invention that would be.. carrot digester..

Why should a nest built by a human be defined as artificial and a nest built by a bird as natural?

Dear Marcel,

Your question has two forms: 1. Is a stimulus produced by humans artificial or natural?

2. Is 'artificial' an observation or an interpretation of an observation, perhaps depending on the research discipline?

1.      What do you think on a stimulus?

2.      It depends on relationships of the systems; if the observer and the subject of observation belong to the same system, the observation is not artificial. However, the limitations of systems are questionable.

Even the aim of observations may be determinant; if a human observes an animal to kill and eat it, this can be a natural observation. If a human observes birds in order to find whether birds are able to abstract reflexion, this may be artificial approach.   

In a strict sense an observation is always an interpretation of physical observation because of the long way of the physical perception until the arrival and process of primer data in the brain.

Dear Marcel,

I feel the difference lies not in human hand alone, but also in human brain. About the 'nest' and other similar examples. The difference lies in the mind. Whereas the bird's nest is something instinctive, human nest is based on cognition, discrimination and instinct. The human ability to transform nature is different from that of other animals. Hence, the need to draw a line between natural and artificial.

Dear Andras,

let say for simplicity that a stimulus provokes a reaction/response either inside or outside the biological body.

Some people would say that a smile might be artificial (faked) or natural, which implies that emotions would be involved in the definition of what is artificial or natural?

For instance, all human-made objects/products that do not express emotions are artificial, but then how to classify the digested art object 'carrot'? 

https://www.youtube.com/watch?v=9EnchawJ3pA

Dear Marcel,

A smile is natural if comes from the heart, it is artificial if it is a product of interest or bad will.

As to the digestible pseudo-art objects they are similar to the coloured sand pictures created by Buddhist monks. These pictures remember us the variability and ephemeral aspect of life. In case of carrot figures the digestibility is an additional dimension.  

It depends on the nature of human.