Rational human behaviour is qualitatively different from the behaviour of other forms of life. (It is not just more complicated).
This all depends on how you define "rational human behaviour"; I'm not convinced that the definition given (see below) is qualitatively different from other forms of life. Regarding the term, human behaviour is extremely diverse, and everyone seems to have their own definition. For example, in economic theory, economics is seen as a study of what constitutes rational human behaviour in the endeavour to fulfil needs and wants; it makes the assumption that human beings will aim to fulfil their self-interests. Rational behaviour can be either a term used to explain how people behave (i.e. to make a model that makes sense of their behaviour (since it makes sense to them), so that other people who do not behave that way can understand them) or behaviour that is based on reasoning (which suggests a Spock like Vulcan, devoid of emotions). When the two are confused, we are tempted to say somebody is acting "irrationally", which usually means that we cannot understand the reasoning behind it, but also tends to suggest that there is no reasoning behind it; there is an element of judgement.