Since 1984, scientists have utilized ancient DNA to explore questions regarding extinct species, beginning with the recovery of DNA from the museum’s Quagga specimen, a zebra-like creature that vanished in the 19th century. Over the past four decades, advancements in technology have enabled researchers to analyze legacy DNA from various animals and plants within the Greenland Ecosystem.
But what about the longevity of DNA? Given that DNA preservation is influenced by numerous environmental factors, scientists continue to grapple with how long DNA can last, both in theory and practice.
Michael Crichton’s sci-fi classic “Jurassic Park” (Knopf, 1990) showcases a bioengineering team extracting dinosaur DNA from amber-trapped insects, making it the gateway for generations, including scientists, to the study of ancient DNA and attempts to revive extinct species.
“Researchers have started searching for DNA from Cretaceous fossils of creatures that existed 145-66 million years ago,” said Gilbert, “and they found DNA resembling that of relatively modern bacteria.”
In a groundbreaking study co-authored by Gilbert, 2012 research employed statistical models to establish the “half-life” of DNA in bone, affirming the remarkable preservation chances of DNA found in Cretaceous specimens.
The research team examined mitochondrial DNA from 158 bones belonging to extinct New Zealand birds with known Carbon Dates. Their investigation into the degradation of DNA over time revealed that, on average, the “half-life” of DNA in a sample was around 521 years.
The predictive model indicates that, under optimal conditions, DNA could endure for roughly 6.8 million years. However, this timeframe is insufficient for turning the concepts of Jurassic Park into reality.
“The ideal conditions for the conservation of ancient DNA include cold, dark, and dry environments,” mentioned Jennifer Raff, a biologist at the University of Kansas, in her comments to Live Science. “Typically, permafrost provides the best scenarios for quality DNA recovery.”
This explains why the oldest DNA discovered to date was found in sediments in Greenland that are 2.4 million years old. The oldest genome previously sequenced was from a Siberian mammoth that lived approximately 1.2 million years ago.
The inquiry now arises: what is the oldest DNA derived from humans or their close relatives? Humans primarily evolved in warm, humid regions where DNA preservation is often inadequate. This limits our understanding of our ancestors and their related species due to the scarcity of DNA.
The DNA of our nearest human relative, the Neanderthal, was extracted in 1997 from a Neanderthal specimen discovered in 1856 in Germany’s Kleinefeldhofer Cave, dating back 40,000 years. Meanwhile, the oldest evidence of DNA from human relatives was obtained from Sima de los Husos (“bone hole”) located in an underground cave in the Atapuerca Mountains of Spain. In 2022, researchers successfully sequenced DNA from the thigh bones of relatives who lived 400,000 years ago, possibly indicating the existence of both Neanderthals and Denisovans.
Evidence of ancient DNA from Africa, the cradle of human evolution over millions of years, remains limited. Due to natural preservation challenges, the oldest DNA from sub-Saharan Africa is approximately 20,000 years old and belongs to modern Homo sapiens. Considering the projected half-life of DNA, this restricts researchers’ ability to delve into the genetics of our primitive ancestors.
Recent advancements in paleoproteomics, the study of ancient proteins, are beginning to supply some genetic insights from human relatives that lived around 3.5 million years ago. However, it remains challenging to extract DNA from ancient kin like Australopithecus, specifically Lucy, as their chances of survival are virtually nil.
“We are not optimistic about retrieving DNA from Australopithecus,” Raff noted, “since they primarily remained in Africa where conditions for DNA preservation are subpar.” However, the potential to extract DNA from more recent hominins exists, as they encompass our close human ancestors.
“I hold a significantly brighter outlook for Homo Erectus,” Raff stated, “as they inhabited areas likely offering optimal DNA preservation, such as the Republic of Georgia and China.”
Even if researchers identify a location with favorable conditions for the preservation of ancient DNA, there remains an essential consideration – the DNA must still be meaningful, as Gilbert explained.
“The essential DNA sequences are quite short. Identifying a book involves recognizing its chapters, which is simpler than defining it at the word or letter level,” he clarified.
2.4 million years stands as the current record for the oldest significant DNA successfully sequenced, but Gilbert suggested that older DNA might eventually be uncovered, possibly under the Antarctic ice sheet.
“In truth, if you had asked in 2003 how long DNA could endure, the prevailing wisdom would have been a mere 100,000 years,” Gilbert recounted. “Now we have exceeded that estimation by twentyfold.”
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Source: www.livescience.com