Humans

Human beings are the dominant race in the world as they outnumber most other races and are usually among the most technologically advanced and organized of the races. 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.

Appearance
Humans within the series are generally 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). Some, such as Edward Newgate and Gekko Moriah, are extremely large for human standards, Moriah being as far as 692cm (22'7") tall, far surpassing an average human's height by roughly five to six times. However, these humans are considered to be no more than "oversized ants" in the face of true giants. These large humans are roughly the same size as wotans. Other humans have features that are unique, such as Usopp's long nose, which led to people mistaking him for a fishman in Cocoyasi Village.

Differences between humans vary greatly; islands not allied with the World Government form a number of tribes including (but not exclusive to) the dwarves, minkmen, Longarm Tribe, Longleg Tribe, and Snakeneck Tribe. Other tribes are expected to exist as ape-like humans including Masira, Shoujou and the Coffee Monkeys have also appeared; Masira himself claimed openly to be human and not ape, although he was not insulted when called a "monkey". As of the Thriller Bark Arc, humans with demonic features have also appeared in the storyline, mainly in the Impel Down Arc. Even amongst families, size and proportional differences may occur, the most prominent example being the Gorgon Sisters.

Biology
Mostly, humans are the same as in real life. The strange tribes of the Grand Line are also human, however they differ significantly in appearance from "normal" humans. Their advantages over normal humans have yet to be explained. It has also yet to be explained how large sized humans occur even among families that produce normal sized humans. Boa Sandersonia and Marigold were normal-sized humans in the past but currently stand noticeably above the size of normal humans, while their oldest sister, once only a little shorter than them, remained normal, if above-average, human size. Amongst the Kuja in particular, there is a notable phenomenon that every child born is female and no males are ever produced. The alterations of other tribes' biology like this have yet to be explained.

Humans can, however breed with merfolk to produce a human-merfolk child. However, further interbreeding with humans removes all apparent merfolk features. After just two generations, the only thing that remains is a "human" with an incredible swimming ability. Since giants are a race of extremely large humans, which can breed with fishmen to produce a wotan, and can interbreed with normal humans as well, as evidinced by Sapi. Humans, fishmen, and merfolk also share the same blood types.

Inter-species Relationships
The weakness of the humans in the One Piece world often makes other races such as the fishmen think lowly of them. Often this reaches 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 mermen as nothing more than fish, dismissing them as "men" thus alienating any chances of them being viewed as equals with humans. Fishmen children were seen to view humans as "scary" and in one case an adult Fishman attempted to blame their vast numbers as a reason for their species ruling the world.

Amongst 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 prices are much higher than a regular human. The tribes and races caught up in the slave trade are often sold for a higher price then "normal" humans. Humans themselves are worth an average of 500,000 in the slave market. Members of these tribes may even regard "normal" humans as freaks due to the fact that where they come from, their own appearances are normal and that of "normal" humans is not.

In stark contrast to the mermen and fishmen, giants are respectfully regarded as "men" by humans.

Overall Strength
Most of the inhabitants of the One Piece world are normal 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 become immensely powerful and gain incredible abilities. Normal humans are more likely to consider using Devil Fruits than 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 Kashi, who are actual giants.

While the normal human is physically much weaker than races like giants and fishmen, their wide range of attacks, skills, and abilities make up for them to be more versatile fighters. Even with the physical strength of other races taken into account, there are a handful of humans that surpass even the great advantages against them, although it is not always in physical strength but in tactical thinking as well. Arlong had blamed the fact they had numbers as a reason for them ruling over Fishmen, who are noted to be physically stronger overall then humans, as he believed that humans were the weakest species overall.

Trivia

 * In the World of One Piece, humans can live up to at least 141 years old (i.e. Kureha).
 * While all races are "man", humans in particular seem to be more inclined to decide what the meaning of "man" is. Thus it would seem that within the One Piece world, to be called "human" and "man" may (in some cases) not mean the same thing. In particular the World Nobles may use discriminative terminology to describe their slaves as "barely human" and will go so far as to burn the hoof of the soaring dragon into their slaves' flesh. As soon as they are marked in this way, the slaves are forever known as "less than human".
 * Tony Tony Chopper classifies himself as a "man" because of his Devil Fruit abilities from the Hito Hito no Mi, although he is a reindeer by species.
 * The existence of strange tribes humans can be likened to the documentation of early explorers and researchers. They often returned from places like Africa, Asia, and the Americas with accounts of tribes who have manipulated their appearances in strange or even what would be considered to such men as grotesque ways.
 * Ironically, despite being known as the weakest species, most of the strongest characters in One Piece are in fact human.