Ancient DNA - Antediluvian DNA Studies

Antediluvian DNA Studies

The post-PCR era heralded a wave of publications as numerous research groups tried their hands at aDNA. Soon a series of incredible findings had been published, claiming authentic DNA could be extracted from specimens that were millions of years old, into the realms of what Lindahl (1993b) has labelled Antediluvian DNA. The majority of such claims were based on the retrieval of DNA from organisms preserved in amber. Insects such as stingless bees (Cano et al. 1992a; Cano et al. 1992b), termites (De Salle et al. 1992; De Salle et al. 1993) and wood gnats (De Salle and Grimaldi 1994), as well as plant (Poinar et al. 1993) and bacterial (Cano et al. 1994) sequences were extracted from Dominican amber dating to the Oligocene epoch. Still older sources of Lebanese amber-encased weevils, dating to within the Cretaceous epoch, reportedly also yielded authentic DNA (Cano et al. 1993). DNA retrieval was also not limited to amber. Several sediment-preserved plant remains dating to the Miocene were successfully investigated (Golenberg et al. 1990; Golenberg 1991). Then, in 1994 and to international acclaim, Woodward et al. reported the most exciting results to date -mitochondrial cytochrome b sequences that had apparently been extracted from dinosaur bones dating to over 80 million years ago. When in 1995 two further studies reported dinosaur DNA sequences extracted from a Cretaceous egg (An et al. 1995; Li et al. 1995) it seemed that the field would truly revolutionise knowledge of the Earth’s evolutionary past. Even these extraordinary ages were topped by the claimed retrieval of 250 million years old halobacterial sequences from Halite.

Unfortunately the golden days of antediluvian DNA did not last. A critical review of ancient DNA literature through the development of the field highlights that few recent studies have succeeded in amplifying DNA from remains older than several hundred thousand years. A greater appreciation for the risks of environmental contamination, and studies on the chemical stability of DNA have resulted in concerns beign raised over previous reported results. The Dinosaur DNA was later revealed to be human Y-Chromosome, while the DNA reported from encapsulated halobacteria has been criticized based on its similarity to modern bacteria, hinting at contamination. Recent work also suggest that these bacterial DNA samples may not have not survived from ancient times, but may instead be the product of long-term, low-level metabolic activity.