So far, biological systems were characterized increasingly complex. Historically, 70 years ago people still thought each phenotype were determined by single gene and evolution was due to change of these genes. While nowadays physiological behavior are determined by so many sophisticated mechanisms, Large-scale signalling and regulatory networks, complex functional proteins and organelles, flexible but robust metabolic fluxes as well as current hot spots, non-coding RNAs and Epigenetic modification of chromatin. Regulation of biological phenomenon are usually astonishingly precise. From an evolutionary point of view, the reason is evolution process was carried in extremely large time scale, fitness of biological systems are incrementally adapted.
According to our current understanding of biological systems it makes the process of evolution a multi-scale one rather than a matter only in genetic level. (It’s undoubted that all these essential variances and diversifications are determined by genetic and epigenetic states though, to crack the complexity of life is far more challenging than investigations on genetics and "epigenetics".) For instance, the development of biological systems has been and will be a mystery in a long time. These molecules work so well that each human develops with quite few defects from a single fertilized embryonic stem cell into a complicated ensemble of specialized cells that function harmonically for several decades in an ever-changing environment.
I was naively thinking that as a result of long time evolution, the survived organisms are very optimized in order to adapt environment. I start to doubt this statement. Reasonably, the results of evolution are survival of biological systems until genetic information inherited by offspring efficiently, nevertheless survived biological systems are not optimized. Research on evolutionary biology provided evidence, gene duplication, non-functional genes, multi-step regulation of single biological process. These mechanisms could be possibly necessary to increase precision of regulation and flexibility of adaptation in evolution, but for an engineer they may be redundant for biological systems itself to implement certain function.
Thus, here questions arose. Could we find a way to make biological systems well optimized more than survivable? Are there any principles underlying nature designed biological systems, any difference with artificially engineered systems? Could we design a better one than nature and time? these are some of the problems that synthetic biology want to figure out. Before that, I think characterizing underlying principles of nature design is a precursory step. No matter with bottom up or top down approaches, systems biology could be a bridge to that gate. Besides, it’s also possible to take another approach of reverse engineering, simply you could think it as using synthetic biology to decipher complexity of biological systems.
These three approaches all have many challenges and tricky problems. Typical ones are temporal and spatial dynamics, genome wide and quantitative investigation, multiple scales integration, precision and reliability of computational or experimental results.
(I kind of like phrases bioscience and bioengineering rather than systems biology and synthetic biology. Well, those are what they were called)