Your ear is fully shaped when you are born, and changes little after about age 10. It does grow larger and begin to sag as you age because of the effects of gravity, but that is a measurable effect; in fact it has been calculated to be just 1.22 mm per year.
So unless you damage your ears, by say getting into a fight with Mike Tyson, it's a pretty reliable measurement.
Research in this area is exploding. A recent study
showed you can even identify gender by 2-D and 3-D images of ears (and women do tend to have smaller ears than men). Of course you can easily hide ears with hair, hats, scarves and other clothing, but when a profile is all you have to work from to identify someone, that unique ear shape could be very helpful.
The eyes have it
Look in the mirror at both your eyes. Now look closely at each iris. That's the muscle that opens and closes your pupil to control the amount of light that enters your eye. You'll see small, random patterns of texture in one of your irises, which are completely different from the texture in your other iris. How does that happen?
While your DNA does set the ultimate color and structure of each iris, the furrows, rifts and pits you see happen randomly during fetal development in the womb. It's called "chaotic morphogenesis," and is thought to occur when iris tissue tightens and folds
as the fetus opens and shuts its developing eyes. Just like fingerprints, identical twins don't share the same iris swirls and patterns, so each of their irises is also unique.
Because the iris is protected behind the cornea, it was long though that these unique patterns never changed, making an iris identification nearly foolproof. However, recent studies show the iris does degrade
, perhaps from age or from damage, such as contact lens use
Still, researchers such as Marios Savvides
of Carnegie Mellon's CyLab are excited by the possibilities. "As long as the part of the eye over the iris region remains unaltered from disease then iris recognition will not be affected," said Savvides. "We are working on extracting iris features from high resolution visible photos and matching them against other high resolution photos of irises" and have been able to match those, which is "an exciting finding."
"We have also demonstrated capturing an iris from a person in a stopped vehicle to depict the scenario where a police officer could identify who the driver is before approaching. Iris recognition and in particular long-range iris recognition can [also] help identify victims of human trafficking or abduction and alert authorities," added Savvides.
You can tell by the way I walk
No, I'm not talking about John Cleese's "Ministry of Silly Walks." You don't have to be that outrageous to be identified by your gait.
"Several decades ago researchers put lights on ankles, knees, hips and figured out you could recognize friends by the way they walk," said University of Notre Dame biometrics expert Kevin Bowyer
. Today computers can identify a person in a crowded city block by their walk.
Nixon pioneered much of the research in gait analysis. "We removed every other variable we could to test the hypothesis, which is why we used a green screen,
" he said. "All we had was a person walking in a series of images. We look at the motion of the body and the body parts, then measured those with a computer to get a set of numbers. And as long as we get the same set of numbers for each person, we can achieve recognition."
Nixon recently put his computers to the test in a murder trial in Australia. "The guy killed a man and his wife in a shop. He had cased the joint in the morning and we had surveillance footage of him. Then when he came back in the evening he wore a mask and gloves and covered his head. All we could see of him was the way he walked. We presented evidence that the gait was the same; the guy put his hands up and said 'Yeah, it was me'."
The mouth has spoken
The next time someone sticks out their tongue at you, take a closer look. See all those tiny bumps and ridges? "It's the different distribution of size and shape, just as fingerprints," said Bowyer, that makes your tongue unique to you and no one else. The bumps contain more than 10,000 taste buds, each one filled with microscopic hairs called microvilli. Microvilli function like tiny food critics, sensing if your meal is sweet or sour, salty or bitter, and sending reviews up to the brain.
Your voice is another way to identify you, and each of us have unique characteristics
formed by the length of our vocal tract, the frequency and intensity of our vocal quality, and how we've learned to speak. Because it's so easy for someone to mimic another voice, you have to use a computer to tell the differences, and science is working hard on that.
Each person's set of teeth is also unique, but that's because of what you do to them, like clenching or grinding or sucking your thumb. Because of those environmental differences, even identical twins do not have exactly the same set of teeth.
Dental records are often used to identify a body in forensics, but you don't see anyone running out to take tongue prints, although it is the only internal body organ that can quite easily be exposed for inspection. Say ah!
The window into your nervous system, and maybe your soul
The very back of your eye, the part where light rays focus, is called the retina. The pattern of blood vessels displayed there is a very precise snapshot of your nervous system — unique to you. While it's widely used in the animal world
to verify the identity of show cattle and purebred horses, as well as track food safety and disease outbreaks, use in humans has been limited.
Except in your eye doctor's office. The retina is the only place in your body where doctors can see your central nervous system without surgery
. Ophthalmologists can see first signs of diabetes, multiple sclerosis, high blood pressure, even brain health
during your annual checkup.
Fingerprints no longer the gold standard
No one else has your exact fingerprints, even your identical twin. How can that be? It starts when you're a fetus, between 1 and 3 inches long, and the pads on your fingers and palms begin to grow. As the skin forms and thickens over the next month or two, it comes into contact with other structures in the womb, which start to create ridges on the skin of the fingertip.
The density of your mom's amniotic fluid, how much you move, and your position in the womb are all thought to affect how those ridges form.
"Where the lines end or join is determined randomly," Bowyer said. "We know you're supposed to have 10 fingers and 10 fingerprints, but the detail of the pattern isn't predictable."
By the time mom is in her sixth month of pregnancy, your fingerprints have fully formed the arches, loops and whorls we use to match fingerprints
, with lots of other unique patterns scattered in between.
Once considered the "gold standard" of identification, fingerprints have lost some of their luster because they can be degraded or damaged, such as by chemical burns or having a career as a bricklayer. In one case, a man lost his fingerprints when a common cancer drug
caused the skin to peel. Still, fingerprints are commonly used by law enforcement, forensics and companies such as Apple for personal identification.
Recent studies believe we can now even tell gender from fingerprints
Some people are born without fingerprints. It's called adermatoglyphia, and is a very rare disorder caused by mutations in the SMARCAD1 gene. According to the National Institutes of Health, it's also called "immigration delay disease
" because those who have it have lots of problems when they try to enter countries requiring fingerprinting for identification.
DNA is still the gold standard
DNA, or deoxyribonucleic acid as it is rarely pronounced, is the genetic formula that tells your cells how to build you into you, and no one else.
Think of your DNA as four Legos that like to play in pairs along a spiral staircase called a double helix. Those pairs (A and T; C and G) form building blocks of code called genes that become the blueprint for your hair, eyes, body shape and everything else that makes you unique.
There are nearly 20,000 human genes, created from about 3 billion bases, so it's easy to see why no other human will have the exact same pattern of DNA
. Unless you have an identical twin, right?
But wait, that truism is no longer true. Breakthrough studies
in the last year show even identical twins have different DNA. Using second generation genome sequencing
, said Bowyer, "you find that once that fertilized egg splits there are random mutations that are happening and that can be used to identify differences between twins."
Called single nucleotide polymorphisms, or "Snips," these "typos" in the DNA sequence
are being studied to shed light on how we differ in our response to drugs, environmental toxins and why one of us might get a particular disease, even if our twin didn't.