Can genetically modified animals help ease the shortage of organs? After years of research into xenotransplantation, the field is at a turning point — yet risks and ethical issues remain.

Picture your body: It’s a collection of cells carrying thousands of genetic mistakes accrued over a lifetime – many harmless, some bad, and at least a few that may be good for you.

Population and animal studies suggested it could treat cancer, but the clinical trials were a bust. Here’s what happened and what potential may remain.

Some go gently into the night. Others die less prettily in freak accidents or deadly invasions, or after a showy display.