Eliminating endogenous
retrovirus in a step toward
xenotransplantation
pp. 1238 & 1303
CRISPR
PIGS
New hope for China’s
left-behind kids p. 1226
A twist on photoemission
delay pp. 1239 & 1274
How pesticides should
be regulated p. 1232
$15
22 SEPTEMBER 2017
sciencemag.org