Cercia Director, Prof. Xin Yao, gave an invited keynote speech at the Sixth International Workshop on Information Processing in Cells and Tissues (IPCAT’05), August 30 – September 1, 2005, York, UK, on “Why Use Populations in Evolutionary Computation”. IPCAT’05 is a highly interdisciplnary workshop with roughly 50% participants from biology and computer science/engineering, respectively.