OPENSIVE MIND// THE KB
Due to the considerable anthropological, archaeological, and public interest directed toward human remains, they have received
considerable attention from the DNA community. There are also more profound
contamination issues, since the specimens belong to the same species as the
researchers collecting and evaluating the samples.
Sources:-
Due to the morphological preservation in mummies, many
studies from the 1990s and 2000s used mummified tissue as a source of ancient
human DNA. Examples include both naturally preserved specimens, for example,
those preserved in ice, such as the Ötzi the Iceman, or through
rapid desiccation, such as high-altitude mummies from the Andes, as
well as various sources of artificially preserved tissue (such as the
chemically treated mummies of ancient Egypt). However, mummified remains
are a limited resource. The majority of human aDNA studies have focused on
extracting DNA from two sources that are much more common in the archaeological
record – bone and teeth. The bone that is most often used
for DNA extraction is the petrous bone, since its dense structure
provides good conditions for DNA preservation. Several other sources have
also yielded DNA, including paleo faeces, and hair. Contamination
remains a major problem when working on ancient human material.
Ancient pathogen DNA has been successfully retrieved
from samples dating to more than 5,000 years old in humans and as long as
17,000 years ago in other species. In addition to the usual sources of
mummified tissue, bones and teeth, such studies have also examined a range of
other tissue samples, including calcified pleura, tissue embedded
in paraffin, and formalin-fixed tissue. Efficient
computational tools have been developed for pathogen and microorganism aDNA
analyses in a small (QIIME) and large scale (FALCON).
Results:-
Taking preventative measures in their procedure against such
contamination though, a 2012 study analyses bone samples of a Neanderthal group
in the El Sidon cave, finding new insights on potential kinship and genetic
diversity from the aDNA. In November 2015, scientists reported finding a
110,000-year-old tooth containing DNA from the Denisovan hominin, an extinct species of human in
the genus Homo.
The research has added new complexity to the peopling of Eurasia. It has also revealed new information about links between the ancestors of Central Asians and the indigenous peoples of the Americas. In Africa, older DNA degrades quickly due to the warmer tropical climate, although, in September 2017, ancient DNA samples, as old as 8,100 years old, have been reported.
Moreover, ancient DNA has helped researchers to estimate modern
human divergence. By sequencing African
genomes from three Stone Age hunter gatherers (2000 years old) and four Iron
Age farmers (300 to 500 years old), Schlebusch and colleagues were able to push
back the date of the earliest divergence between human populations to 350,000
to 260,000 years ago.
