A Fourth is a fictional type of being in the novel Spin.

Spin (novel)

Spin is a science fiction novel by author Robert Charles Wilson. It was published in 2005 and won the Hugo Award for Best Novel in 2006. It is the first book in the Spin trilogy, with Axis published in 2007 and Vortex published in July 2011.-Plot:Set in the near future, Spin begins with the sudden...

The Fourth State

The Fourth State is an upgrade performed on human beings. The process uses an engineered virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 to edit harmful components out of the subject's DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

. The Fourth treatment was developed on Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

.

It should also be noted that the Fourth treatment is somewhat modular, as after the original treatment, additional upgrades may be added.

Societal impact

On Mars, the Fourth State is considered coequal with normal adulthood. Fourths are unable to vote in normal elections, but are the only ones allowed to vote for members of a particular ruling body. The Fourth treatment is available for free to anyone.

On Earth, the American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 government hunts Fourths. This was one of the reasons for Diane and Tyler to enter the new world.

Possible upgrades

At present, only one upgrade is known.

• Basic Fourth: The most basic form of the Fourth Age. No upgrades other than increased empathy
  Empathy
  Empathy is the capacity to recognize and, to some extent, share feelings that are being experienced by another sapient or semi-sapient being. Someone may need to have a certain amount of empathy before they are able to feel compassion. The English word was coined in 1909 by E.B...
  
  and edited DNA.
• Nanomachine Channel: Enables possessor to listen in on Martian nanomachines. Latent until fall of Spin membrane. Lethal once active, as Hypotheticals begin attempting to consume possessor.

Notable Fourths

• Wun Ngo Wen (upgrades unknown) (deceased)
• Jason Lawton (basic Fourth, nanomachine channel) (became Fourth to cure AMS) (deceased)
• Diane Lawton (basic Fourth) (became Fourth to cure CVWS)
• Tyler Dupree (basic Fourth)