In the first week of this month (1 May 2008), an article appeared in Nature (Volume 453, Number 7191) that can be viewed as an important step toward unraveling the real structural properties of networks, including the biological ones. In their publication, the researchers in Santa Fe Institute suggest that hierarchy is a central organizing principle of complex networks which can be used to discover missing relationships between entities. Probably the most interesting part of their work is development of novel algorithms (based on the hierarchical organization) which are able to “predict” the missing links from partial data with high accuracy. Even when only half of the connections in three networks were shown to their algorithm, the researchers found that hierarchical structure can predict missing connections with an accuracy of up to 80 percent.
Although their algorithm worked well on 3 types of network (the metabolic network of the spirochete Treponema pallidum, a network of associations between terrorists, and a food web of grassland species), it would be interesting to see how this approach can contribute to increasing our understanding of the systems biology of human complex diseases, including cancer.