FORENSICS 169: KEEPING TRACK OF NONHUMAN CLUES
This essay might be of special interest to writers of detective and mystery novels who would like to enrich their stories by providing their readers with a gift of extra details. It might also be of general interest to many other readers, especially those who are CSI and NCIS fans.
Especially during World War II and somewhat since, to advise followers that persons had been at a particular place, it has been common for Yanks to mark exposed locations using the words KILROY WAS HERE, for Brits to use the words MR. CHAD WAS HERE, for Aussies to use the words FOO WAS HERE and for dogs to simply use a spray of urine. In a dog’s case, the mark also makes other dogs aware of the boundaries of what the marking dog considers its range and/or territory to be.
For some yet-to-be-agreed-upon reason, dogs seem to have a natural affinity for urinating on vehicle tires. In 1999, an Iowa woman working in her own front yard was attacked by a man who attempted to sexually assault her. He was unsuccessful and fled in his vehicle. The woman was not able to pick her attacker out of a subsequent police line-up, but she remembered his vehicle. She also remembered that her dog had tinkled on one of its tires. An analysis of DNA in urine obtained from the suspect’s vehicle tire confirmed that it had indeed been supplied courtesy of the woman’s dog. Faced with this evidence, the attacker pleaded guilty and was sentenced to two years in prison. According to an animal genetics expert, when defendants learn that animal DNA evidence will be used against them, most will negotiate a plea agreement.
Reportedly, the first case that brought the subject of cat DNA into a courtroom began in 1994 when a mother of five disappeared from her home on Prince Edward Island, Canada. A virtual path leading from her home to a courthouse was anything but direct. It led from the victim’s home to her blood-spattered car, which was discovered a few days later. The path continued to a shallow grave, where her body was discovered several months after that. A short time previously, the path had swung past a location about six miles from her home, where a military unit had discovered a plastic bag containing a leather jacket. The jacket had the victim’s blood and a number of white hairs on it. Police had hopes that the hairs would help identify the victim’s killer, but analysis revealed that the hair was not human. It was cat hair.
Cats are fastidious self-groomers, many spending as much as half their awake time licking themselves. Such grooming removes parasites and dirt and keeps the cats’ fur fluffy and free of mats. It also removes loose hair. As a result of the latter, visitors seldom depart a cat-furnished house without having some souvenir cat hairs clinging to them. The estranged husband and father of three of the murder-victim’s children owned a white cat. The path thus led to his being considered a suspect in his wife’s murder. Police tried to have DNA from the hair on the jacket compared to the DNA of the suspect’s cat. At this point, however, the path seemed to have reached a dead end. To their surprise, they learned that such a comparison had never been done and that, apparently, nobody wanted to do it. Fortunately, they eventually found a laboratory that, although it specialized in the study of genetic diseases, agreed to help; and a method was developed to do so. Random tests of 20 cats on the small island were performed to ensure their DNA was not all the same. The DNA that had been discovered on the jacket was found to match that of the suspect’s cat. The path reached a successful end in court when the submission of evidence including that of the DNA comparison resulted in a jury finding the suspect guilty of murdering his wife.
For some time, material containing DNA had often been collected at crime scenes; but it had not been used as evidence. Fortunately, the establishment and use of animal DNA databases are now being expanded and the forensic evidence they yield put to good use. TV viewers have probably seen CSI and NCIS personnel use CODIS (Combined DNA Index System) to “almost instantly” identify suspects by their DNA. Interestingly, a CANINE CODIS has been established especially to help prevent dog fighting.
A CANINE CODIS (Combined DNA Index System) has even been established especially to help prevent dog fighting.
Many readers probably know that DNA comprises four base chemicals paired and repeated to form the well-known double helix known as desoxyribonucleic acid. Genes make up a specific portion of a cell’s DNA. We know that each human has about 25,000 genes, but all their functions are not yet understood. They are known, however, to carry instructions for constructing proteins and whatever else is needed by a person’s body to, for example, digest food, produce energy and grow. Genes form bundles known as chromosomes. Humans have 23 pairs of chromosomes. One pair, designated XX or XY, determines a person’s gender and a few other characteristics. XX chromosomes yield females and XY chromosomes yield males. Other pairs determine remaining characteristics. A complete set of an organism’s hereditary information is known as its genome. The human genome was mapped in 2003.
Every eukaryotic cell (a cell having a nucleus) has nuclear DNA (nDNA) within its nucleus. Cells also contain cytoplasm, which includes everything else in the cell. Large numbers of mitochondria, which are the cells’ main energy source, can reside within the cytoplasm; and they perform many functions necessary for life. They are of forensic importance because they carry their own DNA, known as mitochondrial DNA (mtDNA), which is different than nDNA. Given the abundance of mtDNA, they provide a much better chance of being found in a condition of being forensically useful.
Interested readers might find some extra bits of information in my previous essay in the Storytellersunplugged archive. It is titled FORENSICS 126: KNOW YOUR MITOCHONDRIA and is dated February 19, 2010.
DNA evidence can remain investigatably usable for a finite time, but the time depends on the conditions of its environment. To date, a permafrost site in an area of Canada’s Yukon known as Thistle Creek has apparently done the best job of preservation. The permafrost is the oldest known to exist, and it topped the previous preservation record by a factor of ten when DNA was recovered from bones of a horse (Equus lambei) that lived some 700,000 years ago). The find is of special significance because it implies that even older DNA of other animals, including human ancestors, might be found in permafrost in condition to enable the mapping of their genes. Movie fans and some geneticists are also wondering about the possibilities of cloning versions of the presently extinct.
The estimated 700,000-year age of the discovered horse bones places them within a geologic period known as the Pleistocene Epoch, or the Great Ice Age, the end of which corresponds to the end of the last glacial period. A recent estimate places the period as stretching roughly from 2.6 million to 11,700 years before present (BP). It was during this period that the ancestors of modern humans are thought to have evolved. It was also during at least a portion of this period that it is believed that mastodons, mammoths, saber-tooth cats, cave bears and great American lions also roamed the Earth. Both mammoths and mastodons thrived during the early Pleistocene, leaving their fossilized remains to be discovered in almost every US state. Reportedly, more than 250 mastodon remains have been found in Michigan. In fact, the remains of a mastodon were recently unearthed near my home. They had been preserved in a shallow lakebed adjacent ancient white-spruce tree cones. Spruce tree forests are thought to have been a favorite mastodon habitat.
Prince Edward Island is a Canadian province located in the Gulf of St. Lawrence. In addition to a main island, the province actually comprises 231 more, minor islands. It was named after Prince Edward, Duke of Kent and Sthrathearn. He was King George III’s fourth son. Readers might not be familiar with Edward’s name, but his daughter’s name might ring a bell. She was Queen Victoria.
Thank you, dear readers, for taking time to scan my words. As always, I look forward to having you join me here on the nineteenth days of future months. Past posts are to be found in the Storytellersunplugged archive.