Problems With Ancient DNA

The efforts of scientists to extract and study ancient DNA are not always successful. In many cases ancient DNA simply does not exist inside the sample or the DNA fragments are too small to be identified. Ancient DNA is also prone to chemical modifications that can alter its genetic code and make it difficult to analyse.

Another problem is the contamination of the samples with DNA from fungi and bacteria that invaded the tissues at, or after, the time of death. The DNA from these micro-organisms is often more abundant than the DNA of the animal or plant being studied. Ancient DNA samples can also become contaminated with the DNA of modern organisms, including humans.

Most successful ancient DNA studies involve specimens less than 100 000 years old. Initial claims that DNA could easily be recovered from material many millions of years old now seem unrealistic. In fact, some of the earliest and most startling claims of ancient DNA being extracted from fossilised plants and amber entombed insects up to 125 million years old have been shown to be false. The DNA extracted was actually a mixture of human, insect and bacterial DNA.