We saw from the discussion of systems that it is the interactions between the parts of a system that give rise to its emergent properties. Let's consider what happens to the number of possible interactions as the number of parts of a system increases. In the simplest case, a system has just two parts, and there can be only one interaction between these two parts. However, within a system with four parts, there are 11 possible modes of interaction. Among a class of 20 students there can be 190 possible interactions, counting just the pairwise interactions. And among the approximately 25,000 genes that comprise each human being, there are more than 336 million possible pairwise interactions… since genes interact in more than pairs, the total number of possible interactions is staggering!   Clearly, some simplification is necessary for us to approach understanding a system of such potential complexity.

We are mindful of the total number of possible interactions among the parts in an organism. There can be thousands, even tens of thousands of genes and proteins interacting within an organism to trigger some function in an organism. (Remember, it is the interaction of parts in a system which gives rise to its emergent properties - i.e., its novel function.)

Fortunately for research scientists, biological processes have been found to operate exactly the same in many different organisms. The "Krebs cycle" (the process cells use to extract energy from sugars) is the same across most species. Hemoglobin (essential for blood to carry oxygen to cells) is the same across different species. Because biological processes operate the same in various species, including both very simple and very complex life forms, scientists can use simpler organisms for their initial studies of biological systems.

We call this sort of simpler study case a "model organism". The simplicity of a model organism allows a scientist to more easily zero in on the properties and functions of interest, without having to sort out the complexity arising from additional systems embodied in more complex organisms. For instance, scientists can study yeast cells to understand how sugars are metabolized in many species (including in humans), without having to deal with the additional complexity from other systems in complex organisms (such as contracting muscles). Moreover, small organisms (such as yeast cells) reproduce quickly, allowing biologists to study multiple strains and generations of an organism in a short time.

Model organisms are carefully selected to provide simple cases for our initial studies of biological systems. They simplify our initial research, yet still provide data-rich and flexible experimental "systems" for us to examine. They are vital to our initial biological discoveries. Research findings from model organisms must be confirmed by also studying humans. But studies on model organisms are crucial to eventually answering the central biological questions regarding human life.

You might imagine studying a light bulb would be relatively straightforward, and one scientist could develop the expertise to probe and fully understand it. It also might be the case when studying the simplest of model organism. Imagine you were a scientist trying to probe the mysteries of the overnight-package-delivery-service "system" we mentioned earlier. Given the complexity of all the parts and subsystems embodied in this system (e.g., aircraft, truck delivery fleets, computerized tracking and scheduling systems, etc.), it would be difficult for one person to probe and understand this system in its entirety. There are limits as to how much one person can figure out, especially if they were examining the system from the outside (i.e. standing at the customer-service counter, or outside the fence at the airport).

The complexity of biological systems goes well beyond that of the overnight package delivery service system. Because of this, we rely on the expertise of scientists from multiple disciplines to probe and fully understand the properties of biological systems. In fact, it is the collaborative efforts of scientists cooperating in an interdisciplinary environment which is critical to advances in systems biology. This collaborative and interdisciplinary research is one of the unique and crucial aspects of our research at the ISB.

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