Program for Evolutionary Dynamics, Harvard University, Cambridge, Massachusetts, United States of America. dingli@fas.harvard.edu|Program for Evolutionary Dynamics, Harvard University, Cambridge, Massachusetts, United States of America. dingli@fas.harvard.edu|Program for Evolutionary Dynamics, Harvard University, Cambridge, Massachusetts, United States of America. dingli@fas.harvard.edu|Program for Evolutionary Dynamics, Harvard University, Cambridge, Massachusetts, United States of America. dingli@fas.harvard.edu