A black tiger is a rare color variant of the tiger and is not a distinct species or geographic subspecies. There are unconfirmed reports and one painting (now lost) of pure black non-striped tigers (true melanistic tigers), but no physical evidence. What was thought to be a black tiger was either a black jaguar or a black leopard. Most black mammals are due to the non-agouti mutation. Agouti refers to the ticking of each individual hair. In certain light, the pattern still shows up because the background color is less dense than the color of the markings. So-called black tigers are due to pseudo-melanism. Pseudo-melanistic tigers have thick stripes so close together that the tawny background is barely visible between stripes. Such tigers are said to be getting more common due to inbreeding. They are also said to be smaller than normal tigers, perhaps also due to inbreeding or because large black leopards are misidentified as black tigers. A discussion of black tigers was presented by British cryptozoologist Dr Karl Shuker in his book Mystery Cats of the World.