Paranthropus through the looking glass

Abstract

Most research and public interest in human origins focuses on taxa that are likely to be our ancestors. There must have been genetic continuity between modern humans and the common ancestor we share with chimpanzees and bonobos, and we want to know what each link in this chain looked like and how it behaved. However, the clear evidence for taxic diversity in the human (aka hominin) clade means that we also have close relatives who are not our ancestors (1). Two papers in PNAS focus on the behavior and paleoenvironmental context of Paranthropus boisei , a distinctive and long-extinct nonancestral relative that lived alongside our early Homo ancestors in eastern Africa between just less than 3 Ma and just over 1 Ma. Both papers use stable isotopes to track diet during a largely unknown, but likely crucial, period in our evolutionary history. The first fossil evidence of P. boisei , two upper milk teeth, a very large molar, and a tiny canine, was discovered in 1955 at Olduvai Gorge, in Tanzania (2). The mystery of the owner of the unusual teeth was solved in 1959 when Mary Leakey recognized fragments of a fossil hominin cranium eroding from a hillside. The Olduvai Hominid (OH) 5 cranium had a small ( ca. 500 cm3) brain—not much bigger than that of a gorilla and about a third the size of that of a modern human—a flat and broad face, large attachment areas for chewing muscles, small incisors and canines, and exceptionally large premolar and molar tooth crowns. Louis Leakey proposed a new taxon, Zinjanthropus boisei (3) for OH 5, but within a few years the new genus was dropped in favor of Australopithecus , or Paranthropus ; the latter is our preference. More evidence of P. boisei came in 1964 with the discovery … [↵][1]1To whom correspondence may be addressed. Email: bernardawood{at}gmail.com. [1]: #xref-corresp-1-1