Scientific racism justified colonisation by framing domination as:

The question asks how scientific racism justified colonisation by framing domination.

• Scientific racism is a pseudoscientific belief that certain racial groups are inherently superior or inferior based on biological or evolutionary differences.
• During the colonial era, this ideology was used to rationalize the subjugation and exploitation of indigenous populations. Colonizers often claimed that their race was more "evolved" or "civilized," thus giving them a right or even a duty to dominate and "improve" other societies.
• The case study mentions the promotion of "ideas of civilisation and progress" by the European mission, which aligns with the concept of a perceived evolutionary or cultural superiority.

Let's examine the options:

• a) Evolutionary superiority: This directly corresponds to the core tenets of scientific racism, which posited that some races were more advanced in an evolutionary sense, justifying their dominance.
• b) Democratic: Colonisation is fundamentally undemocratic, involving the imposition of external rule rather than self-governance.
• c) Religious tolerance: While the mission introduced Christianity, scientific racism's justification for domination was not based on religious tolerance; rather, it often involved the suppression of indigenous beliefs.
• d) Random: Domination under scientific racism was presented as a natural or justified outcome, not a random one.

Therefore, scientific racism justified colonisation by asserting the evolutionary superiority of the colonizing power.

The final answer is $\boxed{\text{a. Evolutionary superiority}}$.