The joke was not about software specifically, but about the whole system, everything. But even software feels like evolutionary forces are at work - when you work on huge systems developed and added-to over years, sometimes decades, often by new people (lots of churn, contractors), the "design" is less and less visible and it becomes a mess, the role of deciding whether a new "gene" (feature/big fix) works is taken by the (also messy) huge test suite and since nobody understands the whole system any more people code to pass those tests. I made the comparison looking back at when I once was part of those adding to a huge existing piece of software without understanding (it had become impossible, the only objective was to have the tests pass, or even just most of them).

When I later also took biology classes (and org. chem., biochem., physiology etc etc) I could not help but see parallels - I say parallels, not transferring the models over! - to how we develop huge systems, be it software, hardware or the combination of both. No single human understands even a significant part of them any more. "Deliberate design" is not the sole force working on those systems any more.