One Amino Acid Refiled a Denisovan Face
Lysine where everyone else has arginine. The bones had been filed under other names.
Yesterday's file had the first confirmed Denisovan radius, a few centimetres of arm bone. Today's item is a different paper and a different question: the face.
Qiaomei Fu and colleagues report in Nature that proteins from a skull fragment and a jaw fragment at Xujiayao, dug up between 1976 and 1979, carry a Denisovan marker. Position 996 of the collagen COL1A2 is lysine. Neanderthals and modern humans have arginine there. Both Xujiayao bones had lysine: 57 peptides in the skull sample, 61 in the jaw, and one stray arginine peptide in each. A tree built from 2,074 amino-acid positions put both samples inside Denisovans with over 99 percent support.
The shape they attach to that identification is a low, wide, thick braincase, a receding forehead, a heavy brow, rectangular eye sockets, flat cheeks, a flat nasal bridge, and a jaw that does not project much. The back of the skull is more vertical than in Neanderthals or modern humans. Some of these fossils had been proposed as Homo longi or Homo juluensis. The amino acid refiled them.
The Rational Explanation
One marker is a strong hint, not a genome. Protein survives where DNA does not, and it carries less information. A reconstruction is a model wearing hair.
What We Don't Know
How much of "the Denisovan face" is this population and how much is the species. The Harbin skull, already called Denisovan, shares the heavy brow and the flat midface. The radius from yesterday is still a different bone.