Archaeologist

An archaeologist is a particular type of historian who ventures out into the field to find ancient ruins and study them first-hand. They are interested in the cultures of lost civilizations. They work to uncover things lost beneath the earth over time, and are eager to make new discoveries about the past. Archaeologists serve a most invaluable role of piecing together the development of countries, people, and cultures.

In the real world, archaeologists are praised for their work. Often they employ locals to act as guides and labor from nearby villages close to the place they are digging up. Many countries like Egypt thrive on the efforts of their work over the years.

Other countries may approach the idea of allowing archaeologists into an area for fear that they are spies working for other governments.

One Piece
In One Piece, the World Government does not mind archaeology taking place. However should any archaeologist (or person at all) research the Void Century or the Poneglyphs, they risk being sent to jail or killed, and if not captured, a very high bounty may be placed on their head.

Ohara Island boasted the most famous archaeologists in the world, and their Tree of Knowledge held the history of countries from around the world. They were eventually destroyed when the World Government found out they were researching forbidden histories; all save Nico Robin, who had a bounty put on her head as a result of her escape from death, were killed.

Most people in One Piece seem uninterested in the past and are unaware of the Void Century. Archaeologists are not completely scorned by people (unless they research the forbidden histories, then they are considered evil) around the world. However, due to the Ohara incident there appear to be few archaeologists left, as well as a combination of all of the above factors, means that very few crews have archaeologists as they are not essential. However archaeologists are far from useless, since with their knowledge and experience, finding ancient treasures become much easier. An example is when Robin discovered where the "Lost City of Gold" was in one day, something Enel took a long time to accomplish.

Trivia

 * Though Robin's role on the ship seems a little odd, it was not unheard of for there to be at least one crew member who was knowledgeable on the value of items such as jewels, other treasures or even merchant cargo, along with knowledge on where they originate from. In raids and attacks on others, time along with carry capability of both a ship and its crew would have limited what items the pirates could steal, having someone with knowledge on the most valuable of any given set of items would have proven invaluable to any pirate crew.