New Human Ancestor Highlights Problems with Homo

Everyone, scientists and nonscientists are alike, are abuzz with news of the new human “ancestor” that has recently been found in a cave in South Africa. Or at least, everyone should be.

There has never been a find like this before. Thousands of well-preserved hominin specimens coming from at least 15 different individuals… yeah, that kind of discovery is well beyond what any paleoanthropologist would even dream of. And yet, there she is: Homo naledi, in full skeletal glory.

New Human Ancestor Highlights Problems with Homo - Clapway

For comparison, all we have found of Homo tsaichangensis is one side of a single jaw bone with some teeth. For Homo cepranensis, all we have is the top part of one skull. To be fair, many scientists are doubtful that those specimens really come from distinct species, rather than just atypical variants of Homo erectus (of which we have a great many fossils). However, you see the point. Mother earth guards fossils jealously and usually doles them out tiny bits at a time.

New Human Ancestor Highlights Problems with Homo - ClapwayJaw and teeth of Homo tsaichangensis (photo by TaichungJohnny); partial skull of Homo cepranensus (Mounier, et al. PLOS One 2011).

Not so with H. naledi and no one questions that this hominin is distinct from anything seen before.

But there is a problem. The scientists that made this discovery, led by Lee Burger of the University of the Witwatersrand in South Africa, coined it Homo naledi. Naledi comes from the name of the cave where the discovery was made and means “star” in the local Sotho language. The decision to include the species in the genus Homo, while certainly in keeping with current practice in paleoanthropology, could cause a problem that has been brewing in the field to finally boil over: the Homo genus is a mess.

The problem is one of boundaries. Unlike most genera, Homo has never been clearly defined with objective and consistent criteria. This vagueness dates all the way back when the genus was first created by Carl Linnaus in 1758. His idea of a “defining character” was simply saying Nosce te ipsum meaning “know thyself.” Not real helpful. Since no hominin was known other than modern human beings, there was no possibility of confusion at the time. Since then, however, dozens of other hominins have been unearthed.

Jeffrey Schwartz and Ian Tattersall, two high-profile paleoanthopologists, wrote in Science magazine just last month that, “…the boundaries of both the species and the genus [Homo] remain as fuzzy as ever, new fossils having been rather haphazardly assigned to species of Homo.” Others have bemoaned the problem as well. Last year, Bernard Wood wrote in Nature that, “the genus has an incoherent mishmash of features,” particularly when H. habilis is included. It is the inclusion of habilis that is responsible for much of the confusion, according to Wood, and what has led to the cramming of ever more species into Homo.

The spectacular discovery of Homo naledi will surely make matters worse. It has an upper body more similar to the Australopithecus genus, but upright posture similar to members of Homo. The cranial capacity is substantially smaller than other species of Homo, but the hands appear advanced in that they appear adapted for fine-motor control. Those same hands, however, are long and curved, as if they hadn’t fully left behind the arboreal lifestyle.

Often, such is life in the world of taxonomy. Hairs must be split and decisions must be made. However, in the case of the Homo genus, there aren’t universally accepted criteria by which to split those hairs.

As beautiful as Homo naledi is, her genus could use some sprucing up.

History is fascinating, as the news about our new human ancestor reveals:



Nathan H. Lents is a Professor of Molecular Biology at John Jay College of the City University of New York. He also maintains The Human Evolution Blog and is the author of the upcoming book, "Not So Different: Finding Human Nature in Animals" (Columbia University Press, 2016). When he's not writing, his lab studies the bacteria that feast on dead humans (no, really) and forensic botany.