And if you're too lazy (it is pretty long) then read this excerpt.
"Since the early 1960s biologists have realized that genes are neither blueprints nor dictators; instead, as I will explain in a moment, genes are better seen as providers of opportunity. Yet because the brain has for so long been treated as separate from the body, the notion of genes as sources of options rather than purveyors of commands has yet to really enter into our understanding of the origins of human psychology.
Biologists have long understood that all genes have two functions. First, they serve as templates for building particular proteins. The insulin gene provides a template for insulin, the hemoglobin genes give templates for building hemoglobin, and so forth. Second, each gene contains what is called a regulatory sequence, a set of conditions that guide whether or not that gene’s template gets converted into protein. Although every cell contains a complete copy of the genome, most of the genes in any given cell are silent. Your lung cells, for example, contain the recipe for insulin but they don’t produce any, because in those cells the insulin gene is switched off (or “repressed”); each protein is produced only in the cells in which the relevant gene is switched on. So individual genes are like lines in a computer program. Each gene has an IF and a THEN, a precondition (IF) and an action (THEN). And here is one of the most important places where the environment can enter: the IFs of genes are responsive to the environment of the cells in which they are contained. Rather than being static entities that decide the fate of each cell in advance, genes—because of the regulatory sequence—are dynamic and can guide a cell in different ways at different times, depending on the balance of molecules in their environment.
This basic logic—which was worked out in the early 1960s by two French biologists, François Jacob and Jacques Monod, in a series of painstaking studies of the diet of a simple bacterium—applies as much to humans as to bacteria, and as much for the brain as for any other part of the body. Monod and Jacob aimed to understand how E. coli bacteria could switch almost instantaneously from a diet of glucose (its favorite) to a diet of lactose (an emergency backup food). What they found was that this abrupt change in diet was accomplished by a process that switched genes on and off. To metabolize lactose, the bacterium needed to build a certain set of protein-based enzymes that for simplicity I’ll refer to collectively as lactase, the product of a cluster of lactase genes. Every E. coli had those lactase genes lying in wait, but they were only expressed—switched on—when a bit of lactose could bind (attach to) a certain spot of DNA that lay near them, and this in turn could happen only if there was no glucose around to get in the way. In essence, the simple bacterium had an IF-THEN—if lactose and not glucose, then build lactase—that is very much of a piece with the billions of IF-THENs that run the world’s computer software.
The essential point is that genes are IFs rather than MUSTs. So even a single environmental cue can radically reshape the course of development. In the African butterfly Bicyclus anynana, for example, high temperature during development (associated with the rainy season in its native tropical climate) leads the butterfly to become brightly colored; low temperature (associated with a dry fall) leads the butterfly to become a dull brown. The growing butterfly doesn’t learn (in the course of its development) how to blend in better—it will do the same thing in a lab where the temperature varies and the foliage is constant; instead it is genetically programmed to develop in two different ways in two different environments.
The lesson of the last five years of research in developmental neuroscience is that IF-THENs are as crucial and omnipresent in brain development as they are elsewhere. To take one recently worked out example: rats, mice, and other rodents devote a particular region of the cerebral cortex known as barrel fields to the problem of analyzing the stimulation of their whiskers. The exact placement of those barrel fields appears to be driven by a gene or set of genes whose IF region is responsive to the quantity of a particular molecule, Fibroblast Growth Factor 8 (FGF8). By altering the distribution of that molecule, researchers were able to alter barrel development: increasing the concentration of FGF8 led to mice with barrel fields that were unusually far forward, while decreasing the concentration led to mice with barrel fields that were unusually far back. In essence, the quantity of FGF8 serves as a beacon, guiding growing cells to their fate by driving the regulatory IFs of the many genes that are presumably involved in barrel-field formation.
Other IF-THENs contribute to the function of the brain throughout life, e.g., supervising the control of neurotransmitters and participating (as I will explain below) in the process of laying down memory traces. Because each gene has an IF, every aspect of the brain’s development is in principle linked to some aspect of the environment; chemicals such as alcohol that are ingested during pregnancy have such enormous effects because they fool the IFs that regulate genes that guide cells into dividing too much or too little, into moving too far or not far enough, and so forth. The brain is the product of the actions of its component cells, and those actions are the products of the genes they contain within, each cell guided by 30,000 IFs paired with 30,000 THENs—as many possibilities as there are genes. (More, really, because many genes have multiple IFs, and genes can and often do work in combination.)"
This post has been edited by CaptainBaconMan: 21 January 2011 - 01:29 AM