FECAL TRANSPLANT UPDATE: Effects of Aging Have Been Reversed by Putting Young Mouse Poop in Old Mice. “It sounds like something that might have come out of a sci-fi novel, but it’s based on cold, hard, printed research: transplanting fecal microbes from young mice into old mice seems to reverse key signs of aging in the guts, eyes, and brains of the older animals. Further experiments showed that it works the other way too – moving microbes from the poop of aged mice into younger mice caused the younger animals to then show signs of aging, including increased inflammation in the brain and a reduction in a key protein needed for normal vision.”