July 3, 2017

Preserving specimens in situ for future researchers

by David Warmflash

There’s an old joke that there were five paleoanthropologists for every hominin fossil. It’s based partly on truth, which should give you an idea of the rarity of such finds. A major part of what we know about how Australopithecines — not a species, but an entire extinct genus — walked upright grew out of the study of one particular specimen, the famous Lucy, unearthed by Donald Johanson and colleagues in 1974 in Ethiopia. Hominins comprise the subcategory of primates that we consider to be human, ancestral to humanity, or related closely to such ancestors. They include species within two genera: Australopithecus, which were more ape-like but with some more human features, and Homo, our own genus, whose other members were more in the direction of ourselves. Since the discovery of ‘Neanderthal man‘ (known officially as¬†Homo sapiens neanderthalensis, a subcategory of our own species) in the 19th century, the unearthing of hominin specimens has occurred at a turtle’s pace.

The pace changed slightly in 2013, however, when scientists located remains of several individuals of a species that came to be known as Homo naledi, in the Rising Star Cave system of South Africa. By 2015, the number of bone and tooth specimens identified in the caves had grown to more than 1,500, accounting for at least 15 individual H. naledi skeletons species in the caves. While the number of individuals may now be around 18, it still makes the total collection of hominin fossils small around the world. But there are enough H. naledi skeletons available that allow researchers to do something that traditionally was not the usual plan: they are leaving many specimens inside the cave system and doing things to preserve them, in situ, or in place, for study by paleoanthropologists of future decades and centuries.

Dinaledi chamber

A fascinating, and still developing, story surrounds dating of the fossils to 335,000-236,000 years old — a surprisingly young age considering that some researchers have noted that they look similar to Homo erectus, a human ancestor, yet with features primitive for H. erectus and a much smaller cranial volume. The cranial volume is only slightly larger than that of chimpanzees, which suggests that very recently — during a time when brand new research out of Morocco says that the modern form of our species, Homo sapiens sapiens, was already walking the Earth– there were still small brained, but upright walking hominins.

Comparison of skull features of Homo naledi and other early human species ©Chris Stringer, Natural History Museum, UK

The story of how excavators have been able to reach the H. naledi remains is also fascinating. The Rising Star Cave system is a maze of caverns connected by curving, narrow tunnels. Accessing a cavern called the Dinaledi Chamber requires climbing down through an almost vertical tunnel, and passing through an opening that is just 18 centimeters (7 inches) wide. The research team recruited paleoanthropologists with not just caving experience, but also very small, narrow bodies — six women who came to be known as the “Underground Astronauts.”

These specimens are being left for future researchers because technology will keep getting better. Expecting this is a normal thing and it’s part of an evolution within paleoanthropology research. Today, rather than open fossilized bones, as researchers did in the past, they image the bones with computed tomography (CT) scanning and other technologies. This keeps the specimens in good shape even when they are taken out of the excavation site. Back in the late 19th and early 20th centuries, however, paleoanthropologists delved into the fossils with every technology that they had. After all, this was an era when humans thought that they were reaching a technological peak. Who would have thought that, 100 or 150 years later, there would be precise imaging at the macroscopic and microscopic scale, or that it would be possible to extract DNA and analyze it? They didn’t even know about DNA back then. Today, however, we expect technology to keep advancing in leaps and bounds. We have Moore’s Law that says computing power will keep doubling every year or two, and we project this idea onto DNA technology, and pretty much everything else.

It may represent a kind of overconfidence in human technological progress, but in this case it’s a kind of selfless overconfidence, for it gives credit to future generations. It means that in some situations we are thinking about the long term. In a very real sense, it’s the science research equivalent of the people who used to spend their lives on multi-generational projects building cathedrals. Can we start to think this way about other aspects of human civilization?

David Warmflash

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David is an astrobiologist and science writer. He received his M.D. from Tel Aviv University Sackler School of Medicine, and has done post doctoral work at Brandeis University, the University of Pennsylvania, and the Johnson Space Center, where he was part of the NASA's first cohort of astrobiology training fellows. He has been involved in science outreach for more than a decade and since 2002 has collaborated with The Planetary Society on studying the effects of the space environment on small organisms.