Representation by sortition is defined as “democratic” while representation by election is defined as “aristocratic”. Sortition is a democratic instrument because this way people are represented by “their peers” while in an election-based system people are choosing “the best” as “leaders” (= electoral aristocracy).
To illustrate the aristocratic nature of the electoral system, we can take the example of (what may be a somewhat romanticized description of) pirate ships. A hundred years before the French Revolution, pirate ships were run on lines in which liberty, equality and fraternity were the rule. On a pirate ship, the captain was elected and could be deposed by the votes of the crew. The crew, and not the captain, decided whether to attack a particular ship, or a fleet of ships.
The ancient Greeks (circa 400 BC) used the electoral system for the designation of “the best” as military generals. The legislative institutions, however, were based on democratic instruments: representation by sortition and the people’s assembly. Using an electoral system for legislative institutions mainly finds its origins in the Roman Republic .