The lesson of the Jurassic Park tragedy was clear — man and dinosaur were not meant to coexist. It’s lucky then that dinosaur fossils are far too old to contain any genetic material that could be used for cloning. DNA breaks down over time, even when kept in ideal conditions, and a study of extinct moa bones has revealed an estimate of the half-life for our genes.
It might be odd to think of DNA having a half-life, as it’s usually associated with radioactive material — but as it measures the time taken for half of something to decay, it makes sense to talk about old samples of DNA in the same way. For example, uranium-235, the fissile material that can be used in nuclear power plants (and nuclear weapons), has a half-life of 703.8 million years. DNA, by comparison, doesn’t fare so well — according to a study of 158 samples of moa bones between 500 and 6,000 years old, DNA appears to have a half-life of around 521 years.
A study in the Proceedings of the Royal Society B saw palaeogeneticists from the universities of Perth and Copenhagen drilling into the bones of 158 different moa, the largest of the flightless birds which used to dominated New Zealand’s odd and unique ecosystem before the arrival of humans. The bones had all been collected from within a five kilometre radius, and they were estimated to have been buried at an average temperature of 13 degrees Celsius since the birds died. Their similar preservation conditions were key to ensuring that a reliable figure for the DNA decomposition could be found.
Averaging out the results from the different bones gave the average half-life of 521 years. That result is caveated, of course, as there are many factors that can also affect the rate of decay — soil acidity, bone health, extreme temperature, humidity, and so on. However, it does provide a baseline against which to assess the viability of obtaining DNA samples from future finds.
If there is a lot of DNA, preserved in absolutely ideal conditions, then it might hang around for several thousand years. Samples of Neanderthal DNA have been found in ancient teeth as old as 100,000 years old, and New Scientist reports that there have also been tiny fragments of DNA from insects and plants hundreds of thousands of years old found in ice cores, but these are too decayed to be used for cloning.
The moa could theoretically be cloned, if a good enough DNA sample is found. The moa is generally thought to have been hunted to extinction by the Maori residents of New Zealand before the arrival of European settlers in the 1700s, which isn’t too long enough by DNA standards. Or, a better candidate might be the woolly mammoth — intact specimens have been found frozen into the permafrost (including very recently by a boy out walking his dog), and it is thought that it will eventually be possible to implant a mammoth embryo into an elephant’s uterus, which will grow into a full-on baby mammoth. We may even be able to reintroduce them into the wild, which is really the least we could do after driving them to extinction in the first place.
Ian Steadman, Wired UK