Police Dogs Can Distinguish Identical Twins

From ScienceMag
BY SARA REARDON

Being an identical twin might seem like a great way to fool a DNA test and get away with the perfect crime. But furry forensic experts can make sure justice is served. In a new study, researchers instructed a group of children, including two sets of identical twins and two sets of fraternal twins, to swab the insides of their cheeks and place the swabs in glass jars. Working with ten police German shepherds and their handlers from the Czech Republic police, the researchers then ran a mock crime scene investigation. The handler presented one twin’s scent to the dog and then told it to go find the matching scent in a lineup of seven jars, which included the other twin’s scent. In twelve trials per dog, none of them ever identified the wrong twin as a match, the researchers report online this week in PLoS ONE, even though the children lived in the same home, ate the same food, and had identical DNA. No word yet on whether these dogs will be getting their own CSI spinoff.

Reference
Pinc L, Bartoš L, Reslová A, Kotrba R (2011) Dogs Discriminate Identical Twins. PLoS ONE 6(6): e20704. doi:10.1371/journal.pone.0020704

Abstract
Earlier studies have shown variation among experimental attempts to establish whether human monozygotic twins that are genetically identical also have identical individual scents. In none of the cases were the dogs able to distinguish all the individual scents of monozygotic twins living in the same environment if the scents were presented to them separately. Ten specially trained police German Shepherd dogs of three Czech Republic Police Regional Headquarters were used for scent identification in our study. The dogs were supposed to match scents of two monozygotic pairs (5 and 7 years old) and two dizygotic twin pairs (8 and 13 years old). Scents were collected on cotton squares stored in glass jars. Dog handlers were blind to the experiment details. In each trial (line-up), one scent was used as a starting scent and the dog was then sent to determine if any of the 7 presented glass jars contained a matching scent. Scents of children of similar ages were used as distractors. In the matching procedure, the dogs matched correctly the scent of one twin with the other, as well as two scents collected from every single identical and non-identical twin to prove their efficacy and likewise, the presence of the matching twin scent in any given glass jar. All dogs in all trials distinguished correctly the scents of identical as well as non-identical twins. All dogs similarly matched positively two scents collected from the same individuals. Our findings indicated that specially trained German Shepherd dogs are able to distinguish individual scents of identical twins despite the fact that they live in the same environment, eat the same food and even if the scents are not presented to them simultaneously.