Evolved Hardware

I somehow missed the work of Jon Bird and Paul Layzell - the former also from COGS at Sussex University, where Adrian Thompson hailed from.

Brilliant paper from 2002, showing hardware evolvolution making full use of it's environment.

https://thinkingdeeper.files.wordpress.c...-radio.pdf

It has proved difficult to clarify exactly how these circuits
work. Probing a typical one with an oscilloscope has shown
that it does not use beat frequencies to achieve the target
frequency. If the transistors are swapped for nominally
identical ones, then the output frequency changes by as much
as 30%. A simulation was created that incorporated all the
parasitic capacitance expected to exist within the physical
circuit, but the simulated circuits failed to oscillate. The
programmable switches almost certainly play an important
role in the behaviour of the circuit and it is only possible to
probe their input and output connections and not the circuitry
in which they are embedded.

Some of the circuits achieved high fitness, but when they
were examined with an oscilloscope they did not oscillate
stably: the signals were of the order of 10 – 50 mV amplitude
with rapidly fluctuating frequency. The evolutionary process
had taken advantage of the fact that the fitness function
rewarded amplifiers, even if the output signal was noise. It
seems that some circuits had amplified radio signals present
in the air that were stable enough over the 2 ms sampling
period to give good fitness scores. These signals were
generated by nearby PCs in the laboratory where the
experiments took place.

In earlier experiments Layzell [25] found that circuits
utilised the oscilloscope used to measure their behaviour as a
path to 0V, via the 10 MΩ impedance of the oscilloscope. If
the oscilloscope was unplugged, the circuit did not work. In a
SPICE simulation where the oscilloscope was represented by
a resistance, the circuit worked, confirming its functional
role.
Some of the evolved oscillators worked successfully until a
soldering iron on a nearby workbench was disconnected from
the mains, at which point oscillation ceased. This occurred
despite high quality laboratory power supplies and extensive
mains filtering. The circuit was apparently sensitive to tiny
transients in its voltage supply. The circuit worked if it was
reinstantiated on the Evolvable Motherboard, regardless of
whether the soldering iron was on or off. However, tests
showed that it failed to oscillate if during instantiation the
programmable switches were set in a different order to that
used originally.
It seems that the circuit was dependent on some initial condition,
such as charge, that only occurred if the switches were set in a
particular sequence.
These results demonstrate that unconstrained, intrinsic
Hardware Evolution will potentially exploit any physical
characteristic that can influence circuit behaviour, and that
these characteristics are present in the entire evolutionary
environment. The fact that the circuits sometimes utilise
very particular environmental conditions and component
properties does mean that they do not always generalise well.