On Thursday, millions of Americans will celebrate Thanksgiving with a turkey that could never exist in nature.

They will carve a bird with an oversize breast and legs too puny for walking. After more than a half-century of genetic engineering, today’s mass-produced, sterile turkeys look and taste nothing like the rich-flavored, long-legged birds enjoyed at Thanksgivings from the original feast in 1621 through the 1940s.