Dr. Thompson decided to test the idea by creating a circuit that could distinguish between two different inputs, one at 1kHz and one at 10kHz. Depending on the input the circuit should output either zero or five volts. This sort of circuit is simple for an engineer using conventional methods of constructing electrical circuits. However, to ensure that the evolved circuit would have to take a unique approach he provided only a fraction of the number of components (a mere 100) compared to more conventional circuits, as well as deliberately providing no system clock. To enable this circuit to change he used chips that could change their internal logical structure for whatever task was assigned to them called Field Programmable Gate Array (FPGA) chips. Enough of these could become any device with the right programme loaded into them. He then set up each chip to have a random initial program and, having fed in the two audio codes, he programmed a computer to assess the effectiveness of the configurations. The best were allowed to intermingle and the process repeated with a few minor random mutations in the programme between generations.
And so the process went on and on, but within a few hundred generations the circuit was beginning to change function. By generation 220 it basically just replayed the input signal. By the time it had passed 600 it was starting to become sensitive to 1kHz, at about generation 1,500 it could tell the signals apart about half the time and finally, after about 4,000 generations, it settled on a program that differentiated between the two exactly as hoped. Spurred by this success, the Sussex team even managed to get it to tell the difference between the spoken commands “stop” and “go”.