The stronger the pheromone signal, the more other ants followed that route. Shorter paths were thus self-reinforcing. Run for 5,000 rounds or so, the ant group-mind would evolve a fairly optimal global route. The Milan group played with variations. By varying parameters, the group came up with a number of computational ant searches.
Ant algorithms are a type of Lamarckian search.
When one ant stumbles upon a short route, that information is indirectly broadcast to the other vants by the trail's pheromone strength. In this way learning in one ant's lifetime is indirectly incorporated into the whole colony's inheritance of information. Individual ants effectively broadcast what they have learned into their hive. Broadcasting, like cultural teaching, is a part of Lamarckian search. Like the evening news.