For as long as there have been humans, there have probably been ideas that we would today call humanist.
These ideas have become so widely held, in the UK and the rest of Western Europe at least, that the Oxford Companion to the Mind even goes so far as to say that it is a predominant, though unacknowledged, world view in the Western World today: "a morally concerned style of intellectual atheism openly avowed by only a small minority of individuals (for example, those who are members of the British Humanist Association) but tacitly accepted by a wide spectrum of educated people in all parts of the Western World."
People who are humanists certainly do have a view of the world that is completely naturalistic, and so they are atheists or agnostics. This is important for some humanists, for whom the non-existence of supernatural forces makes the value placed on human responsibility all the greater. For other humanists, the non-existence of gods is not so important and we may never think about it, once we’ve satisfied ourselves that it is the case. Either way, far more important to humanists than what they don’t believe in is what they do.
A humanist is someone who believes that morality does not have some supernatural origin but that it derives from our need to live together in communities. This conviction leads naturally to a concern that our actions should contribute to the happiness and welfare of both ourselves and others. When someone who is a humanist comes to consider what is right and what is wrong (not just on a grand scale but in our everyday choices), the benefit or harm that it will bring to those around us, to wider humanity - including future generations - and the world are the only factors which matter. Individual rights and freedoms are important to humanists, but individual responsibility, social cooperation and mutual respect are just as important.
A humanist is also someone who believes that the best way to understand the reality around us is through knowledge gained by experience and reason. For some humanists this is just a truth that we have to acknowledge in order to gain any meaningful understanding of how the world around us works, (though the discoveries we make by employing this method – in medicine, for example – can certainly lead to improvements in the lives of many people). For other humanists, the wonder of discovery and the excitement of invention are ends in themselves for the enjoyment and fulfilment that they bring which give meaning and purpose to life.
Meaning and purpose does seem to be what all human beings desire for their lives, but in a universe which we now know to be devoid of ultimate meaning or purpose (or where, even if there is a purpose, it certainly has little to do with humanity), the question of what meaning there can really be in our lives may seem a difficult one. A humanist, however, responds to this question positively. By adopting our own worthwhile goals, by seeking to be happy and to make it easier for others to be happy, by taking enjoyment in the wonders of nature and of human art, by valuing that inner life that makes us more than other animals, and by working together to overcome our problems and make the bad times better, human beings can give the human world a meaning and purpose of its own. In fact, the conviction that this present life is the only one we have acts as a powerful spur for humanists towards these goals.
In a godless universe, the job of advancing an increase in what makes our life worthwhile falls squarely to humanity, and humanists are generally optimistic that it is a challenge we can rise to meet.