Center for Theoretical Biology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Peoples Republic of China.|Center for Theoretical Biology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Peoples Republic of China.|Center for Theoretical Biology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Peoples Republic of China.|Center for Theoretical Biology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Peoples Republic of China.