A research team led by Dr. Chaogu Zheng from the School of Biological Sciences at the University of Hong Kong (HKU) has made a significant discovery about the evolutionary age of different type of cells in a small animal called Caenorhabditis elegans (C. elegans). By using single-cell transcriptomic data and refined phylostratigraphy, the team determines the transcriptomic age of individual cells, which means they are able to estimate the evolutionary origin of different cells based on the age of the genes expressed in the cells.