It was never made clear if the Remans were the original inhabitants, or were a mutated offshoot of the original Vulcan colonists, or the result of interbreeding between the original Vulcan colonists and the original inhabitants of Romulus or Remus. Though grotesque, their morphological constitution has much in common with their possible Vulcan progenitors, such as pointed ears, limited telepathic powers, and greater physical strength and endurance than most humanoid species.
Whatever the case of their origins, their grotesque appearance and unique constitution owes much to the race living generation after generation in an intensely hostile and radioactive environment. As eons passed they became more distinct from their ancestors as a result of both natural selection and genetic drift.
The Remans are treated as second class citizens — an undesirable caste within the Romulan Empire. Remus is a prime planet of dilithium mining, and as such, many Remans have been forced into slave labour. Despite this, they are not inherently less intelligent than Romulans, as evidenced by the intellect and telepathy demonstrated by Shinzon's Viceroy.
As a result of the Remans' subjugation and harsh treatment, the Romulan Senate and Praetor were killed in a conspiracy led by Shinzon (Star Trek Nemesis) to gain control of the Empire and use his new starship, the Scimitar, equipped with thalaron radiation weapons and a nearly impenetrable cloak, to destroy every lifeform on Earth (in order to provoke war between the United Federation of Planets and the Empire). It is also known that Remans were used by Romulans as shock troops during the Dominion War. Remans have also been seen as security escorts for Romulan VIPs on Star Trek: Enterprise.