Above: A four-week-old pig embryo containing human cells. Scientists at the Salk Institute in La Jolla, California grew this chimera in 2017. (U.S. Salk Institute/Xinhua/Alamy) Researchers from the United States and China announced in April that they had created the first ever human–primate chimeras. Mixing human stem cells with macaque monkey embryos, the scientists produced creatures with cells from both species. The creation of such beings is deeply troubling, and raises questions about why it was done and where it might lead. What is the point of this research? Will we have monkeys with human features running around the nation’s laboratories? Who is making the decisions about where to draw the line between research we should want and research we shouldn’t?