Ancient DNA
Insects such as stingless bees,[17][18] termites,[19] and wood gnats,[20] as well as plant[21] and bacterial[22] sequences were said to have been extracted from Dominican amber dating to the Oligocene epoch.
When in 1995 two further studies reported dinosaur DNA sequences extracted from a Cretaceous egg,[27][28] it seemed that the field would revolutionize knowledge of the Earth's evolutionary past.
[29][30] The development of a better understanding of the kinetics of DNA preservation, the risks of sample contamination and other complicating factors led the field to view these results more skeptically.
[34][35] In addition to these technical innovations, the start of the decade saw the field begin to develop better standards and criteria for evaluating DNA results, as well as a better understanding of the potential pitfalls.
[31][36] Autumn of 2022, the Nobel Prize of Physiology or Medicine was awarded to Svante Pääbo "for his discoveries concerning the genomes of extinct hominins and human evolution".
[37] A few days later, on the 7th of December 2022, a study in Nature reported that two-million year old genetic material was found in Greenland, and is currently considered the oldest DNA discovered so far.
[7][8] Due to degradation processes (including cross-linking, deamination and fragmentation),[3] ancient DNA is of lower quality than modern genetic material.
[4] The damage characteristics and ability of aDNA to survive through time restricts possible analyses and places an upper limit on the age of successful samples.
Early studies that reported recovery of much older DNA, for example from Cretaceous dinosaur remains, may have stemmed from contamination of the sample.
[43] A greater appreciation for the risks of environmental contamination and studies on the chemical stability of DNA have raised concerns over previously reported results.
[44] The DNA reported from encapsulated halobacteria has been criticized based on its similarity to modern bacteria, which hints at contamination,[36] or they may be the product of long-term, low-level metabolic activity.
[48][49] New methods have emerged in recent years to prevent possible contamination of aDNA samples, including conducting extractions under extreme sterile conditions, using special adapters to identify endogenous molecules of the sample (distinguished from those introduced during analysis), and applying bioinformatics to resulting sequences based on known reads in order to approximate rates of contamination.
[50][51] Development in the aDNA field in the 2000s increased the importance of authenticating recovered DNA to confirm that it is indeed ancient and not the result of recent contamination.
[70] In June 2013, a group of researchers including Eske Willerslev, Marcus Thomas Pius Gilbert and Orlando Ludovic of the Centre for Geogenetics, Natural History Museum of Denmark at the University of Copenhagen, announced that they had sequenced the DNA of a 560–780 thousand year old horse, using material extracted from a leg bone found buried in permafrost in Canada's Yukon territory.
The majority of human aDNA studies have focused on extracting DNA from two sources much more common in the archaeological record: bones and teeth.
Taking preventative measures in their procedure against such contamination though, a 2012 study analyzed bone samples of a Neanderthal group in the El Sidrón cave, finding new insights on potential kinship and genetic diversity from the aDNA.
[91] 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.
A study from 2018 [94] showed that a Bronze Age mass migration had greatly impacted the genetic makeup of the British Isles, bringing with it the Bell Beaker culture from mainland Europe.
