Ever feel like your cat might know a little more than it lets on? Well, you may be onto something. New research suggests that our little feline friends could be surprising sources of evidence when a crime has been committed.
Specifically, a cat's fur can retain enough DNA shed by a person who has been in their vicinity to serve as evidence of a fleeting meeting between the two. This could mean that, even though cats can't be questioned, they might still be able to help identify perpetrators of crime.
The new study is the first to examine how household pets can contribute to DNA transfer, so there's a lot more work to be done. But it represents a positive step towards the future collection of more comprehensive forensic evidence – which, obviously, would be really helpful police investigations.
"Collection of human DNA needs to become very important in crime scene investigations, but there is a lack of data on companion animals such as cats and dogs in their relationship to human DNA transfer," says forensic scientist Heidi Monkman of Flinders University in Australia.
"These companion animals can be highly relevant in assessing the presence and activities of the inhabitants of the household, or any recent visitors to the scene."
In recent years, DNA analysis technology has become so sophisticated that even the most minute traces of genetic material can be relevant for a crime scene investigation. And we messy humans leave our DNA everywhere. Even just brief contact with an object can transfer traces of our genetic material. So-called touch DNA isn't enough on its own to positively identify a suspect, but it can be used to support other lines of evidence, or rule people out.
Touch DNA obtained from a surface doesn't even require the person to touch that surface, necessarily. It can be transported by a number of means, in skin cells or hairs that drift from a passing body, for example. Which is where household pets may play a role.
So Monkman and her Flinders University colleague Mariya Goray, an experienced crime scene investigator, teamed up with forensic scientist Roland van Oorschot of the Victoria Police Forensic Services Department in Australia to see if they could extract traces of readable human DNA from pet cats.
Their study was conducted on 20 cats from 15 households. At the homes of the study participants, the researchers swabbed the fur on the right side of each cat twice, and collected DNA samples from most of the human study participants (one was a minor child who was not sampled). The cat swabs and the human DNA samples were then processed.
In addition, the occupants of the household filled out questionnaires on the cats' daily behavior and habits. This included how often the cat was touched, and by whom, in the household.
Detectable levels of DNA were found in 80 percent of the cat swab samples. For all cats, there was no significant difference between the amount of DNA present, and the time since last contacted by a human, or length of hair on the cat.
The team was able to generate DNA profiles from 70 percent of the cats in the study that could be interpreted well enough to be linked to a human. Most of the DNA was from people in the cat's own household, but on six of the felines, only unknown human DNA was detected.
Two of those cats spent a lot of time in the bed of the child whose DNA was not sampled, which could explain some of the 'mystery' results. The provenance of the unidentified DNA on the four remaining cats is unknown. None of the households had had visitors for at least two days prior to the swabs.
One case was particularly interesting: a two-cat, two-person household. One of the cats, a hairless sphynx, carried the DNA of an unknown third human. The other cat, a short-haired ragdoll, did not. Both cats had interacted equally with the humans in their household.
Possible sources could include direct transport of the DNA from a human, such as by patting, or by the cat brushing against a contaminated surface. The DNA could also have been lingering since the last time the cat had contact with a visitor.
"The mode of transfer of this DNA to the cat, and its persistence on them, is unknown," the researchers write.
"Further research is required on the transfer of human DNA to and from cats, and the persistence of human DNA on cats and what may influence the varying levels of DNA found on cats such as behavioral habits, and shedder status of the owners."
Or maybe that's just what the cat wants you to think…
The research has been published in Forensic Science International: Genetics Supplement Series.