I am curious to know how cells in developing organisms can know which direction to grow in, how much tissue is required and in what proportion, and how to differentiate to the right cells. If we just take the first issue, which is directional growth, I remember from my O-level biology classes that plants grow towards stimuli. How can this be the case for say a fetus inside a womb? It is more likely that some kind of co-ordinate system is encoded into genes. Also, how do cells interpret genetic data? It might sound like a wierd question, but basically there must be some implicit assumptions which would determine that section X of the genes determine height, etc. Even if the gene has instructions within itself that section X determines height, some implicit assumption must still exist in that tells the reproducing cells that the instruction exists! Without those implicit assumptions it would be like having a manual on how to build a car from iron ore, but not having any tools to do it with.