09:25, Tuesday 15 Jul., 2003 Link

Creatures from primordial silicon (New Scientist). Using genetic algorithms and a field-programmable gate array (FPGAs are logic circuits that can have their logic rewritten on the fly), it turns out evolution doesn't stick to the binary system (high/low) that we use. I mean, of course, but better: When evolving a circuit to differentiate between two signals, instead of using a clock to time the frequencies, the circuit used a complex system of feedback loops (like nature). What's more: "That repertoire turns out to be more intriguing than Thompson could have imagined. Although the configuration program specified tasks for all 100 cells, it transpired that only 32 were essential to the circuit's operation. Thompson could bypass the other cells without affecting it. A further five cells appeared to serve no logical purpose at all-there was no route of connections by which they could influence the output. And yet if he disconnected them, the circuit stopped working. It appears that evolution made use of some physical property of these cells-possibly a capacitive effect or electromagnetic inductance-to influence a signal passing nearby".

Incidentally, the digital circuit abstraction layer isn't as solid as it looks. Analogue effects have to be carefully taken into account when designing and using chips. Read Ground Bounce (IEEE Computer Magazine).