The main characteristic of basic instinct is that it is found

Instinct, in psychology, refers to an unlearned, biologically inherited pattern of behaviour that is present in an organism from birth. It does not depend on training, teaching, or individual experience, and it is not confined to any single species -- it is a general biological phenomenon found across living creatures, including humans.

The question asks for the characteristic that captures what basic instinct actually is. Among the given options, only "in all organisms, and it is inborn and natural" names both defining properties together -- universality across living creatures (the sense in which "organisms" is used here, following the standard convention of this pedagogy/psychology exam material) and innateness (being present from birth without being learned) -- matching the definition above.

• only in human beings: restricts instinct to one species, but instinct is also observed across non-human animals -- this option mistakes learned human capacities (language, reasoning, culture) for instinct.

• only in cats and rats: narrows instinct down to two commonly cited example species rather than describing the concept itself.

• only in artists: confuses instinct with a trained, cultivated skill (artistic talent), which develops through practice and exposure rather than being present from birth.

Hence, the correct characterisation is that basic instinct is found in all organisms and is inborn and natural.