Efforts to create human-animal chimeras have rebooted an ethical debate after reports emerged that scientists have produced monkey embryos containing human cells.

A chimera is an organism whose cells come from two or more “individuals”, with recent work looking at combinations from different species. The word comes from a beast from Greek mythology which was said to be part lion, part goat and part snake.

The latest report, published in the Spanish newspaper El País, claims a team of researchers led by Prof Juan Carlos Izpisúa Belmonte from the Salk Institute in the US have produced monkey-human chimeras. The research was conducted in China “to avoid legal issues”, according to the report.