Dulcian

The Dulcians were a race of humanoids, characterised by relative physical weakness, higher-order brains, and zealous pacifism.

Biology
Dulcians looked like humans, but they had larger brains, a binary vascular system, no unnecessary organs, weaker frames and two hearts. (TV: The Dominators)

Technology
The Dulcians were at a relatively high level of technology. They used vision screens in order to communicate with people far away. They had walls which could change colours and would disappear to function as doors.

In order to travel, Dulcians used travel capsules. These travel capsules were small capsules which would fit two people, were completely automated and allowed Dulcians to quickly travel across the planet. (TV: The Dominators)

Culture
The Dulcians were led by the Council, which was turn led by a director. These councils were made of around six Dulcians who discussed the matters of the government. Sub-groups of the Council included the Scientific and Emergency Committees.

Dulcians were a very peaceful race, and outlawed war. They were known for accepting fact and debating actions before doing them. As such, Dulcians were thought not to be curious or adventuresome. They also believed it was undignified to struggle against one's fate.

Dulcian measurements of time included annos (years) and lunars. (PROSE: The Dominators)

History
During the time of the Seventh Council (led by Director Manus), the Dulcians initiated atomic weapons research on what was later called the Island of Death. After seeing the destruction caused by this test, the second council led by Director Olum outlawed wars and preserved the island for future study.

The Doctor visited Dulkis at some point before the Dominators invaded. He didn't seem to know about the Island of Death.

172 years later, Dulkis was invaded by the Dominators, who landed on the Island of Death to absorb the radiation. They planned to take the strongest Dulcians as slaves and then destroy the planet for fuel. The Dulcians, being a peaceful people, were unwilling to fight back. Luckily, the Second Doctor had also arrived on the Island of Death and was able to stop the Dominators' attempts. (TV: The Dominators)