Emotions are an important part of being human. The ancient Greeks saw emotion, or affect, as being one of the two main motivators driving human behaviour; the other one being conation, or intention. People vary, too, in how sensitive they are to other people's emotions, and this sensitivity also affects our everyday interactions. For the most part, social psychologists have tended to focus on the kind of personal love which occurs between two people rather than on love within families. The way in which relationships change over time, and the idea that love can grow from a positive partnership, is part of the rationale underlying arranged marriages. These have been common in many human societies- in fact, the idea of romantic love as the sole basis for entering into a long-term relationship appears to be a relatively recent phenomenon, historically speaking.