Humans

Appearance
The same as in real life, however they come in several sizes ranging from "normal" to much taller (such as in the case of the Mighty Destroyers)

Inter-species Relationships
The weakness of the humans in the One Piece world often makes other Races such as the Fishmen come to think lowly of them. Often this reaches to the point where they inflict heavy racism onto Humans themselves, although not all Fishmen typically think this.

Often this is met by humans with returned Racism towards the Fishmen, sometimes leding to bloodshed.

Overall Strength
Most of the inhabbitants of the One Piece world are Humans and are one of the weakest races on the planet.

While the average human is as weak as in Real Life, with enough training they are able to train themselves to be able to do incredible stunts such as using Super-Human Strength and incredible abilties. Humans are more likely to consider the usage of Devil Fruits then any other creature in the world, and are the leaders in Devil Fruit research.

Some humans are fortunate to be born with a condition known as giantism that makes them grow more then twice the size of a normal human being. Naturally, with no training, these tall humans are amongst the strongest men and women in the world and their size makes other humans reconsider attacking them. Even then, compared with true Giants their size is nothing, as to Giants humans with giantism are nothing but over grown ants.

Trivia

 * Since they outnumber most other races, usually are amongst the most technologically advanced and orgainsed of the races, human beings remain the dominate race in the world.
 * Most islands are inhabbitant by humans, even in the Grand Line, where most of the stronger races such as the Fishmen and Giants are found.