New discoveries of fossilised hominin remains have to varying degrees helped to shape our ever-morphing interpretation of hominin evolution. Homo naledi is a case in point.
Though many worker in the field of palaeoanthropology were disappointed with the confirmed Middle Pleistocene age of the Dinaledi remains, this news nevertheless fills a void in our understanding of Middle Pleistocene evolution.
H. naledi confirms what we have known since the astonishing discovery of Homo floresiensis, namely that small brained hominins continued to thrive in some part of the planet right up to recent times. H. naledi can now join Homo floresiensis in the small brain Middle to Late Pleistocene club.
Palaeoanthropologist can now exercise a high level of skepticism on dating hominin fossilised remains using morphological stucture and statistics. In 2015, palaeoanthropologist John Francis Thackeray concluded Homo naledi to be over 1.5 Ma, while Mana Dembo and her colleagues concluded an age of 930,000 years of age for the Rising Star remains. Though Dembo et al were closer to actual age of the remains, they were still nearly 600,000 years off.
Finally, H. naledi continues to confirm what we have known since the announcement of Australopithecus sediba that hominin evolution features an ever changing mosasicism. With Australopithecine-like shoulders and cranium, while the lower limbs and foot appears more derived.
I recently came across this scientific article in the Journal of Human Evolution entitled, Ancient DNA Analysis of Dental Calculus by Weyrich et al. It reminded me of the research conducted on the Indonesian hominin, Homo floresiensis. So, here I will summarise what we know thus far. Dating to between 95,000 and 17,000 years ago, the hominin was found in the cave of Liang Bua, overlooking the Wae Racang river valley, on the island of Flores. It’s most remarkable feature was the 1.06 m stature of the individual found. Begging the question, how is this hominin related to us and what led to its diminutive stature. Much of the debate was thoroughly summarised in Leslie Aiello’s paper entitled, Five Years of Homo floresiensis, back in 2010. In short, some questioned the validity of naming these individuals a new species of human. Evidence was brought forward to support the hypothesis that these people were suffering from the neurodevelopmental disorder, Microcephaly and other diseases that induce a reduced stature. As time has passed, media sensation abated and researchers had a chance to step back, the majority are now more accepting of the Australian-Indonesian team’s decision to apply the new hominin nomenclature. Much of the debate hinges on skeletal comparisons between Homo floresiensis and other hominins, like us. There is one piece of information that the individuals of Liang Bua have yet to reveal – Deoxyribonucleic Acid.
Two teams of scientists, the Australian Centre for Ancient DNA (ACAD) and the Department of Evolutionary Anthropology at the Max Planck Institute (MPI) attempted and failed to extract DNA from the individual’s teeth in 2006. This was due to the environment in which the hominins were found, which was not conducive to DNA preservation. Christina Adler of ACAD hypothesised that the reason for extraction failure could be due to extraction procedure. In 2007 the ACAD team sucessfully extracted DNA from a pig tooth unearthed at the Liang Bua Cave, which was about 6,000 years old. The team suggested that first, Cementum (calcified root covering) is the richest source of DNA and second, drilling the specimen destroys the very molecule they are after. Armed with this knowledge another attempt to extract DNA from the hominins of Liang Bua is still yet to be carried out. The year 2013, saw the successful extraction of 400,000 year old DNA in Spain, so Floresiensian DNA may still lie within the teeth. I’m hoping, despite the less than ideal high temperatures of the cave sediments, there lies within those hominin individuals such strands of the good stuff.
Returning to the paper I mentioned at the beginning, it is a summary of all we know regarding the extraction of aDNA and steps to take when extracting it from calculus on teeth. Calculus is a hardened group of micro-organisms that appear as a yellow build-up usually around the gum-tooth boundary. The first demonstration of aDNA in Calculus was documented in a paper entitled Ancient Bacterial DNA (aDNA) in dental calculus from archaeological human remains by Preus et al., in 2011. A year later, aDNA was extracted from Neolithic Argentinian and Chilean humans. In that study, five bacterial species gene sequences were amplified by targeted polymerase chain reactions (PCR). By 2014, Warinner et al., used the power of the metagenomic sequencing strategy demonstrated increased resolution, the identification of antibiotic resistence genes and though the specimens were put through an Ethylenediaminetetraacetic acid (EDTA) and bleach treatments, DNA was recoverable.
When analysing hominin diets, microfossils are a large component, but the strides being made in aDNA extraction will mean that the species of plant or animal will be identified or as it usually does, throws up more questions than answers. As of 2021, no progress has been made in attempts to extract aDNA from the Liang Bua hominins.