Humans

Since they outnumber most other races, usually are amongst the most technologically advanced and organized of the races, human beings remain the dominate race in the world.

Most islands are inhabited by humans, even in the Grand Line, where most of the stronger races such as the Fishmen and Giants are found. As slaves, regular humans sell for just 500,000.

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 Jerry). Differences between humans varies greatly, islands not allied with the World Government form a number of tribes including (but not exclusive to) the Dwarves, Longarm Tribe and Snakeneck Tribe.

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 leading to bloodshed. Part of the problem is that Humans tend to think of Fishmen and the Mermen as nothing more then fish, dismissing them as "men".

Amongst the humans themselves, there is an apparent problem with the non-World Government allied tribes. Their freakish appearances (such as having long arms or legs) are often a lure for kidnapping crews at Sabaody Archipelago, who sell them as slaves because their selling rate is much higher than a regular human.

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 more than 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 these tall humans are nothing but overgrown ants. An example of this would be when the Kairiki Destroyers of the Franky family (enormous by human standards) were totally outmatched in combat by Oimo and Kaashi, who are real giants.