When I was taught anatomy, we the heirs of the EB Jamieson tradition were left in no doubt that muscles, nerves, arteries and veins occupied fixed positions in the body. Once transplantation became common this was shown not to be the case. There were variables eg two renal arteries.
Similarly biochemistry has been taught as a fixed system. The implication was that the same fundamental processes went on in each cell in the body. It would appear that the biochemistry of cells is much more random than hither too believed.
Pearson The cellular hullabaloo Nature vol 453 pp 150-153
Identical genes in seemingly identical cells do different tasks. This variation becomes more pronounced as the overall organ becomes older.
The two copies of DNA in the cell are constantly changing shape and structure whilst proteins attach and detach. Such proteins may be activating or suppressing activity. Chaos theory in action. A constant tension between randomness and correction. The switching on and off of processes in individual cells in an organ may be very different. The more fluctuations there are the greater need for suppressing or correcting repressor protein activity. Quite a waste of energy. This activity and flexibility of genes is not universal , some genes are rigid in their activity others are very flexible. ..
Perhaps this system which has many options at any one time is very flexible in its response to the environment eg nutrition and metabolism.
- Martin Eastwood