Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!rex!uflorida!shark!tomh From: tomh.bbs@shark.cs.fau.edu (Tom Holroyd) Newsgroups: sci.bio Subject: Re: Reconstructing cells from DNA Message-ID: Date: 18 Apr 91 15:45:02 GMT References: <1991Apr16.235422.20331@cunixf.cc.columbia.edu> Sender: bbs@cs.fau.edu (Waffle BBS) Organization: Florida Atlantic University Lines: 31 > >The number of digits that a person (or other > >mammal) develops is now known to be determined by chemical waves at > >certain stages of development rather than by direct coding. > > The problem is, what encodes for the source and sinks of the > gradient? This is still a genetic factor. In drosophila, for example, > proper morphogenesis is dependent on how the maternal RNA is distributed > in the initial embryo. That remains quite essentially, genetic. I disagree. There are, initially, no sources or sinks, only a homogenous field with within-field negative feedback. This leads to a symmetry breaking dynamic which, in a totally self- organized fashion - nothing to do with genetics here, only chemical dynamics, *develops* sources and sinks. The precise locations are determined by distance dependent mechanisms and the wavelengths of the self-organized chamical waves. This type of mechanism is much more flexible than a 'hard coded' system. It self-adjusts for small differences between embryos and doesn't beg the question of 'who decides where the fingers go'. It's also non-genetic. But to put it another way: The genes regulate the purely physical process - physical law determines what happens, but the genes have evolved to control these processes. Philosophical point: Fighting against nature is harder than getting nature to do the work for you. Tom Holroyd Florida Atlantic University Center for Complex Systems tomh@bambi.ccs.fau.edu