Humans have a strong tendency towards lawful, organized societies. There is usually a noble class, which makes and enforces laws and owns all land; a bourgeois class, which manages the flow of money in towns by controlling all cosmopolitan business; a class of merchants and craftsmen who make up the lower ranks of the guilds, and a peasant class, including tenants, serfs and freeman farmers. In some places, there is also class of slaves, which has a widely varying level of rights and privileges, as dictated by local law.
Humans have no common language, and their separate languages differ so much that one must understand nearly all of them to understand the speech of all humans.
In addition to their need for understanding, humans have an unquenchable lust for land, wealth and power. Among humans, territorial wars are very common. They do not produce the finest weapons, but they produce weapons in the greatest numbers and with the most speed. A long history of war has shown that no one can stand up to a sufficiently large and determined army of humans for long, not even other humans.
Many stories tell of races which are magical by their very nature, yet when a powerful wizard is mentioned, he is almost invariably human. If magic is more than mere myth, humans are likely to be some of its greatest wielders. On the other hand, humans have a great fear of anything they can not control, and magic is exceedingly difficult to control. Some stories tell of humans destroying magical objects on sight, or engaging in massive witch-hunts, burning anyone even suspected of associating with sorcery, or of going on all-out crusades against everything magical.
Excerpt from The Eighth Life
The world holds beautiful works of art of incomparable complexity; great houses which last for hundreds of years; caves which extend so far and deep that entire civilizations can rise and fall without ever leaving; structures that serve as meeting place to dozens, but which are crafted so subtly that they are indistinguishable from natural objects. Humans produce none of these. Their life spans are short, so what they create is bound to be temporary. Artwork decays in centuries; buildings house only a few generations before they collapse; land cleared for farming reverts to its natural state within centuries.
But Man is capable of greatness. In their haste, humans have been known to create objects of finer quality and more varied use than anything another race could produce with ten times the effort. Human masonry is shoddy, but it expands so quickly that inside of a decade, a bustling town can appear out of nowhere. When buildings collapse they are replaced by new ones, and life continues. It is hardly surprising that humans have come to dominate the world.
Humans are possessed with a need to learn and understand, and to use their creativity and experimentation to create new things. Human literature and art, even if not the most beautiful, are the most varied to be found in the world. It is likely that, were Man the only intelligence in the world, he would long ago have created all the other races in his mind.