Its inky exterior is just a teaser for the darkness within. It turns out the bones, organs and muscles of the Ayam Cemani are all black as well. Only their eggs and blood are not steeped in the deep blue-black that make them the most-pigmented animals we know about — their eggs are cream-colored and their blood is red.

But why? What could possibly cause a chicken’s flesh and bones to appear to have been pickled in India ink? It turns out, Ayam Cemani is the world’s most extreme example of a condition called dermal hyperpigmentation, or fibromelanosis. Some other chicken varieties have this condition to varying degrees — the French La Fleche, the Vietnamese H’Mong and others — but few of their genomes have achieved the complete internal and external blackout you see in the Ayam Cemani. But some come close!

The black variety of the Silkie Bantam, for instance, is an ancient breed from China that has inky black feathers and even grayish-blue meat and bones. The Swedish Svarthöna is completely black as well, and have been found to have the same genetic mutation as the Ayam Cemani — even though they sprung up on different sides of the world from each other.

Strangely enough, scientists believe the mutation that leads to fibromelanosis in chickens is so unusual it most likely happened only once, in a single bird that lived thousands of years ago. No one knows how the gene traversed the globe from one jet-black bird, but Marco Polo wrote in 1298 about black-boned chickens while he was traveling in Asia, so the gene probably made its way around the world via trade routes.