Synaesthesia

Like a mousetrap, if any major element of the human body is taken away, we cannot survive. Yet it is quite clear that humans develop from far simpler structures like the zygote.

I was wondering how advocates of the idea of irreducible complexity account for this dramatic example of a reduction what they themselves contend to be irreducible. Does anyone know?

RufusAtticus

Hmmm, interesting point.

DrLao

You are sort of making the point ID advocates are trying to make with IC. The development of a fully functional adult organism from a zygote works because the development is programmed in the genome in advance. That is how a zygote can produce IC systems.

If you want to extend this analogy to evolution and say that IC systems are produced through programming the changes in advance, ID advocates would likely be all for it. But darwinian evolution doesn't work this way. Traits are selected as they appear. They are not selected for their final, eventual purpose. Not by natural selection anyway.

pz

[ pz dons his developmental biologist's hat ]

The metaphor of the "program" of development is really, really common, but I dislike it very much. It simply isn't true that the organism is prepatterned or predestined or programmed in the genome. It's better to think of it as a vast reservoir of potential that will subsequently follow a trajectory through state space that is strongly dependent on the environment and recursive interactions.

If you want to use the programming metaphor, I think it is more appropriate to think of the zygote as a computer, with a complex species-specific instruction set. The program is the environment. Development is a process in which each step involves the cellular turing machine processing its environment, and generating an internal state change.

I'd say that a zygote generates an IC embryo by following an internally consistent regulatory logic. The pattern isn't fixed -- after all, you can just add a few lithium ions and that same zygote will blithely make an exogastrula instead of a gastrula.