Effect of Genes on brain development

This article by Gary Marcus - Making the Mind is a nice article summarizing the latest research on brain related developments. It primarily claims that the brain is just like any other organ, and genes have control over all aspects of neurons much the same way as they have on other organs. And therefore, genetic tweaking is now made possible controlling aspects of brain development.

But the key question is the inflence of "Nature" vs. "Nurture" i.e. effect of environment on the mind. Gene has two functions: Template to produce specific proteins such as insulin, and a sequence of conditions which enable or disable the production of proteins. So lungs don't produce insulin because the triggers don't exist there. (The if-then- condition doesn't see any "if" part becoming true.) So main question: What is it that makes "if" part fire? It obviously has to do with the position of the cell in relation to complete body. How exactly is this information made available to specific cell?

The claim of the article is that the "then" part comes from environment. For e.g. if your stomach sees grass, it can (in theory, and if there are genes to that effect) produce proteins which can adapt to digesting grass. (Example quoted in article is of E-Coli bacteria, which can switch to digesting lactase if there is no glucose available.)

And then, how do genes affect the behavior? What is known is they do affect. A "loner" worm was converted into "social" worm by altering one gene in those C. elegans worms.

There is also a question of how 30000 genes influence billions of cells in brain as well as throughout the body. It seems like they act bit like compression i.e. information is there - especially when multiple genes combine together to form many more no. of actions rather than just one-to-one mapping. So it is finally just a set of master genes firing at high level which produces low level results. So a centipade may have leg-building "sub-routine" set of genes!

The author's final comments are that "pre-wiring" and "re-wiring" go together and therefore, environment and pre-conditions have equal effect on how the system gets developed. The crucial point is that every technique for rewiring the brain has its origins, in one way or another, in the genome.

The book "The Birth of the Mind" by Gary Marcus is available via amazon:
http://www.amazon.com/exec/obidos/ASIN/0465044050/bostonreview/104-4323884-8189562