We must also define a fitness function.
For example, one can give a subjective judgement from 1 to 5
for the dish prepared with the recipe 2-1-4.
Similarly, the length of the route in the traveling salesperson
problem is a good measure, because the shorter the route, the
better the solution.
Given an individual, we must assess how
good a solution it is so that we can rank individuals. This
is usually a real number.