It’s hair-raising news for criminals on the run. Scientists behind a new study, published in the journal PLOS ONE, have worked out how to identify individuals solely based on the proteins in a single strand of their hair.
While prosecutors already look at DNA from hair as part of investigations, the technique is far from ideal: DNA is easily degradable, meaning it can only be analysed within a certain time period after the crime. But the new technique could even be used to solve historical or archaeological cases, making it far superior to DNA sequencing in many ways.
DNA degradation depends on several environmental factors including temperature, humidity and pH. It is also affected by the activity of bacteria and other microorganisms. In contrast, actual hairs can survive for a long time – sometimes centuries. After bones and teeth, hair is in fact one of the most resistant structures of the human body. The physical flexibility and robustness of the hair structure is due to proteins with a high degree of intermolecular bonds. A single hair is associated with some 300 different proteins.
In order to understand how the protein can be used to identify individuals, it is important to understand that proteins are coded by DNA. This means that a certain level of the genetic variation that we see in different people’s DNA passes into their proteins. In fact, genetic information in the DNA is translated into amino-acid chains that make up proteins.
The authors focused their attention on hair samples obtained from four different groups of people. Three samples were collected from American-European, American-African and Kenyan living subjects. The fourth was collected from two British archaeological excavations, one in London and the second in Kent, dating from about 1750 to 1853 respectively. They also analysed hair samples from 76 living humans of American-European and African descent.