Prehistoric DNA to Help Solve Human-Evolution Mysteries?

John Pickrell in England
for National Geographic News
March 25, 2004

It may be possible to extract DNA from the bones of human ancestors and other hominids who died up to one million years ago, researchers believe. Hominids are primates that walk upright, including humans and extinct human ancestors and related forms.

Experts speaking at a chemistry conference held in Chicago earlier this month argued that ancient genetic material could be used to better understand the relationships among hominids and answer questions about the evolution of speech and other defining traits of humans.

"DNA is a relatively weak molecule, comparatively speaking, yet under certain conditions it persists in the fossil record despite what chemistry [in the lab] predicts," said Hendrik Poinar, a molecular anthropologist at McMaster University in Ontario Canada. Fragments of genetic material may survive much longer in fossils than laboratory experiments have so far predicted, he said.

Revolution in Evolution Studies

The study of ancient human evolution is one of science's most contentious disciplines. Anthropologists are frequently locked in debate on issues ranging from migration to classification of hominid species. However, new molecular techniques may now revolutionize the field, as well as the study of ancient plants and other animals.

DNA extracted from specimens of extinct animals has already been used to show that the Mauritian dodo is a close cousin to the common pigeon. It has also proven that widely varying bones left behind by New Zealand's giant moa birds belong to the massive females and much-smaller males of a single species. Previous analysis of bones alone had led researchers to mistakenly classify the un-sexed remains into a large number of different species.

The key to finding ancient DNA lies in the conditions of preservation, Poinar said. Researchers already know that DNA is relatively easy to extract from tens-of-thousands-of-years-old mammoths buried in Siberian permafrost. But desert caves with constant temperatures and very low levels of humidity can also be surprisingly good at preservation, he said.

In contrast, horse bones left in the open in a moist temperate country such as Germany might be completely stripped of genetic material in less than 50 years.

Laboratory experiments that estimate the rate of degradation of DNA in bone have predicted that large fragments of the molecule are unable to survive longer than 10,000 years in temperate regions, Poinar said. But researchers have already managed to find DNA sequences that have survived much longer.

Poinar led the team that last year extracted DNA from 30,000-year-old fossilized ground sloth dung. That DNA had persisted against all odds in a warm Nevada desert cave and was four times as old as the theoretical age limit predicted for DNA survival at that temperature.

Protein attached to bone can also hold genetic data (protein sequences mirror those of the DNA they are modeled on), and these more robust molecules may persist even longer in the fossil record.

British researchers revealed in 2002 that they had extracted the world's first intact protein sequence from 60,000-year-old frozen bison bones. As yet unpublished findings may soon reveal protein sequences from horses many times older, Poinar said.

Continued on Next Page >>


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