I read a post in facebook few minutes ago and the titular says something about a boy banging a dog, and then the boy broke the dog's leg because the dog bit her little sister and also the boy stabbed the dog many times. The boy was like 6 years and the girl is 2 years old. Some people said: "That is ok, the human is more important than a dog". I keep thinking on that, why we are more important? A friend answer me because we are rational. But with our rationality we are destroying the earth. I'm not a defender of animals but for being rational I dont feel more important. And when I was thinking in all these a question came to my mind: is the rationality an instinct?
It depends both of the definitions of instinct and rationality.
Taking Helmuth Plessner's work The Levels of the Organic and Man, Introduction to Philosophical Anthropology from 1928 [note: the translation is in the making], it is just the way you think:
In Chapter 6.4, he describes instinct as a certain predetermination of action that has broadness, i.e. leaves place for conciousness, difference, correction of behaviour. It is by this the frame/bounding of conciousness. This has to be discriminated from reflex, which is a direct reaction pattern with no broadness whatsoever. Therefore, instinct is left to animals (and humans, as animalic) that can conciously act towards their environment and not only react to changes in their environment (essentially, but not necessarily identical to the difference between animals with or without central nervous system).
Human rationality there could be defined as an ability that coincedentally emerges from having the ability to have distance from the self (self-conciousness, excentric positionality, Chapter 7) together with the ability to to idealize (Ideation is a term taken from Husserl), that is to make a true difference between the particular and a general concept of it. Only by this, we are enabled to be rational, i.e. not bounded by the situation and phenomena.
As rationality would in these terms be part of the specificity of our mode of conciousness and instinct is described as the frame/bounding of conciousness, rationality would in fact be instinct.
But this is only one, although in its total very convincing (only very sketchy here) way to define the terms.
Rationality is a cognitive capability. A capability which must be trained like the capability to speak.
Rationality is not an instinct:
Instinct or innate behavior is the inherent inclination of a living organism towards a particular complex behavior. The simplest example of an instinctive behavior is a fixed action pattern (Wikipedia)
Summing up the main difference: Rationality must be learned, instinct not.