Going by that definition (and what I learned from my neuroscience degree hehe), I don't understand how humans have no instincts. I can see maybe that we often don't act on them, but even someone living a very sheltered life with no exposure to sexual language, education, whatever... will experience sexual urges starting around puberty. Isn't that instinct?
Also I'm not sure I buy the "without improvement" clause, since it seems to me that hunting is instinctual in the cat (or is it not, by this definition) yet a mature cat with some experience will be a better hunter than a kitten.