Posted on Tuesday 19 November 2002 to Story So Far

A lot of recent progress in paleontology has been based on analysis of DNA taken from ancient bones. As an example, sequencing of mitochondrial DNA taken from Neanderthal bones has been helpful in confirming the dominant theory that the Neanderthals were a completely different branch of homo sapiens from modern humans.

But DNA has one problem, it is an extremely complex and fragile molecule and it deteriorates rapidly over time. Estimates of the maximum useful for age for DNA range from 50,000 to 100,000 years. However, a new approach which focuses on sequencing proteins instead of DNA promises to open a window in to species development over millions of years.

Proteins are considerably more robust than DNA and can last in bone for up to 10 million years. While a protein does not contain any where near as much information as DNA, a protein is the expression of a sequence of genes transcribed as a sequence of amino acids. By comparing the sequences of proteins from different animals it is possible to infer important features about their DNA and how closely they are related.

Fossil protein breakthrough will probe evolution

For many years, biologists have deduced evolutionary relationships from the visible features of living animals and fossils. Molecular biology has given them a new tool for living animals - comparing DNA sequences. However, DNA survives for only a short time after death, so paleontologists have been limited to comparing the shapes and sizes of the bones of extinct species. But analyzing ancient proteins now gives them a new option, says Christina Nielsen-Marsh of the University of Newcastle, because their amino acid sequences reflect genetic codes.

The big advantage of proteins is their stability in suitable environments. Pieces of DNA large enough to sequence using sensitive amplification techniques can survive for 100,000 years in permafrost. But osteocalcin, a structural protein that bonds directly to the minerals of bone, lasts much longer. Matthew Collins, also at Newcastle University, estimates that osteocalcin can survive for more than 100 million years at 0 °C, and for some 10 million years at 10 °C. That would be long enough to look back some six or seven million years to the last common ancestor of humans and chimpanzees.