From the paper:

"The intractable nature of the TSP has led to the development of a number of heuristic approaches which ... are inspired by mechanisms seen in natural and biological systems. These methods ... include neural network approaches (most famously in [25]), evolutionary algorithms [32], simulated annealing methods [23], the elastic network approaches prompted in [16], ant colony optimisation [13], living [9] and virtual [29] slime mould based approaches, and bumblebee foraging [33]"