Curiosities in the Caves: Ancient Discoveries Are Challenging Our Definition of “Human”

With the pace of everyday life in the modern world, it can become easy to forget the more fundamental questions we have about who we are, and what it means to be a part of the great enigma that is humankind. 

To borrow the words of historian Felipe Fernandez-Armesto, “As evolution slowly grinds out species, who’s human? Who’s to say? It is tempting to reserve the term human for ourselves—members of the species we call Homo sapiens.” Along similar lines, the late Philip Adler of East Carolina University acknowledged that “Paleoanthropologists continue to dig up specimens that challenge believers in human uniqueness,” and cause us to have to consider what, precisely, it means to be “human.” 

Indeed, with time we may have to drastically rethink the uniqueness of humans in relation to the long line of ongoing hominin discoveries. A more remote possibility—but one which may nonetheless prove to be true—is the discovery of new hominin types that may have existed far more recently, or which might even still exist in small numbers today; a tantalizing, though increasingly unlikely prospect as time goes on. Technologies that are ever-steadily mapping remote corners of the world, in addition to issues like climate change, deforestation, population growth, and other environmental issues would no doubt present considerations in terms of the discovery of any new species, let alone those that might be large mammals resembling humans. 

Nonetheless, several archaeological discoveries in recent years do suggest that unique kinds of early humans probably did, at very least, exist more recently than once believed. 

As far back as 1979, a discovery was made in a cave in the Guanxi region of China that, decades later, would prove to be of remarkable significance in our broader understanding of human ancestry and the curious persistence of hominid types into recent times. Found at Longlin Cave a similar discovery was made one decade later at the Red Deer Cave site in Yunnan Province, China.

Charcoal remnants extracted from the same areas the fossils were tested in 2012, and found to be of remarkably recent ages: the fossils from Red Deer Cave yielded dates of between 14,300 and 12,600 years, while the earlier Longlin Cave discovery dated to even more recently at around 11,500 years ago.

Partial skull (reconstructed) found in Longlin cave in 1979 (Credit: PLOS One, Wikimedia Commons).

Named after the Red Deer Cave, which became the type site for the discoveries, this mysterious group of hominins bore a number of unique features that seem to place them in between modern humans and those of an earlier archaic variety. With the prevalence of Denisovan DNA remnants that exist among human populations in Southeast Asia, it has been proposed that the Red Deer Cave people might have been human-Denisovan hybrids. 

The remains bear remarkable similarities to early archaic human types such as Homo erectus; however, since attempts at extracting DNA from the Red Deer Cave fossils have proven unsuccessful thus far, anthropologists have been at odds over whether to classify these as a new species.

Mandibles recovered from Red Deer Cave in Yunnan Province, China in 1989. (Credit: PLOS One, Wikimedia Commons).

Opinions on the matter are wide and varied. Darren Curnoe, and evolutionary biologist with the University of New South Wales, Australia, gave an enthusiastic statement on the discovery to National Geographic in 2012. 

“We have discovered a new population of prehistoric humans whose skulls are an unusual mosaic of primitive features, like those seen in our ancestors hundreds of thousands of years ago… In short, they’re anatomically unique among all members of the human evolutionary tree.” 

Alternatively, some critics have argued that the fossils may simply be modern humans with an odd appearance. 

Erik Trinkaus, Professor Emeritus of Physical Anthropology at Washington University in Saint Louis, called the discovery “an unfortunate over-interpretation and misinterpretation of robust early modern humans, probably with affinities to modern Melanesians,” stating that the finds were “nothing extraordinary.”

While attempts at gathering genetic information about the Red Deer Cave people have proven unsuccessful so far, could there actually be evidence for similar human relatives in our own DNA?

Recent genomic studies also seem to point to mysterious archaic human types that can also be traced in modern human DNA, but which remain unknown in the archaeological record. 

In other words, we can prove that in addition to Neanderthals and Denisovans, there are at least two other unknown archaic human types that anatomically modern humans met, lived alongside, and even interbred with within the last several tens of thousands of years.

Homo habilis skull reconstruction, which has been compared to certain features present with the Red Deer Cave specimens (Public Domain).

Recently, I reported on a study published in the journal PNAS which detailed genetic evidence for two unrecognized hominin species that existed in Asia. According to the study’s authors:

“At least 3 different hominin groups appear to have been involved in Asia, of which only the Denisovans are currently known. Several interbreeding events are inferred to have taken place east of Wallace’s Line, consistent with archaeological evidence of widespread and early hominin presence in the area.”

In other words, if this recent DNA evidence is any indication, we’re already certain there are indeed “missing links” in our evolutionary past, waiting to be corroborated in the fossil record.

Whether those fossils will be found or not, and later corroborated with evidence found in DNA remains to be seen. However, it is clear enough already from the data discussed here that there are plenty of mysteries about humanity’s past to keep us busy for some time to come.