Category
📚
LearningTranscript
00:00What are you doing?
00:24You are so addicted to that game.
00:35Dear Tim and Moby,
00:36We were wondering, can two different people have the same fingerprints from Mrs. Marchese's
00:42class?
00:43Well, it's possible.
00:45In theory.
00:46Like, maybe out of several hundred trillion people you'd find two matching prints.
00:52But there are fewer than 10 billion people in the whole world.
00:56So it's pretty safe to say no two living humans have the exact same fingerprints.
01:01That's why they're such a useful way to identify people.
01:05Fingerprints are the oldest form of biometric identification, a way to know who someone
01:10is using their physical characteristics.
01:13In ancient times, people used them to sign business agreements.
01:17And they're still one of the most convenient forms of personal identification, unlike a
01:21driver's license or passport, you can't exactly forget them at home.
01:28No one knows exactly why people have fingerprints.
01:31We do know that they improve our sense of touch.
01:34Running your fingertips over a surface creates tiny vibrations.
01:38This helps the nerves in fingertips feel even the finest textures.
01:43People used to think the raised lines of skin helped us grip objects.
01:47That's why they're called friction ridges.
01:50But it turns out that fingerprints actually reduce your grip on whatever you're touching.
01:57Fingerprints develop while we're still in the womb.
02:00It's thought to be caused by one layer of skin growing faster than the other.
02:04The outermost layer of skin is called the epidermis.
02:07That's the part we see on our bodies.
02:10The epidermis itself has many layers.
02:13The bottom one, the basal layer, is where new skin cells form.
02:17As a fetus develops, the basal cells are multiplying like crazy.
02:21But their space is limited by the layers of skin above them.
02:25With nowhere to go, the basal layer starts to buckle and twist.
02:29That forms the ridge patterns that make up fingerprints.
02:33By the time a fetus is 24 weeks along, those patterns are locked in.
02:36Well, fingerprints stretch as we grow, but their unique pattern stays the same.
02:44Even if you cut or injure your finger, the skin grows back with the exact same ridges.
02:49So there's no way to change your fingerprints, not without doing a lot of damage at least.
02:54That's why they can be so useful in police investigations.
02:59Fingerprints have been used as evidence since at least the 1890s.
03:02That's when the patterns were officially categorized into loops, whorls, and arches.
03:08Small details in the ridges, known as minutia, were also identified.
03:12These tiny differences are key to a fingerprint's uniqueness.
03:18Police began comparing prints found at crime scenes to those of suspects.
03:22If two prints had enough minutia in common, it was considered a match.
03:26And that meant that the suspect must have been at the crime scene.
03:30This same basic system is still in use today.
03:35The technology has advanced a lot since then.
03:38Improved imaging can show even the tiniest minutia, including sweat pores and the exact
03:42width of a ridge.
03:44These make it easier to identify who a print belongs to.
03:48Instead of using messy ink and paper, prints can be scanned directly into a computer.
03:54Local police departments can submit prints to the FBI.
03:58They've created a huge database of prints taken from crime scenes and arrest records
04:02from around the country.
04:04Sophisticated programs can quickly identify possible matches.
04:08That helps narrow down suspects with much less work.
04:11No, it's not as simple as it looks in those crime shows.
04:17Crime scenes are covered in thousands of prints, one on top of the other.
04:20On rare occasions, they might be visible, like if they're in wet paint.
04:24But usually, they're left behind by the sweat and oil in our skin.
04:28This invisible kind is called a latent print.
04:31To save a latent print, investigators sprinkle it with a super-fine powder that sticks to
04:36the oil.
04:37Then they can lift the image of the print with a special kind of tape and transfer it
04:40to a card.
04:42Most latent prints are too smudged to use.
04:45And many are left by people who didn't do anything wrong.
04:49Well, like whoever lives there, or people who had a good reason for touching stuff at
04:53the scene.
04:54And it's not like you can just feed the collected prints into a computer and, boom,
04:58find a match.
05:00They have to be carefully cleaned up and then analyzed by experts.
05:04Even then, there might not be enough detail for a match.
05:07And experts might have different opinions on the same prints.
05:10Sometimes in a trial, it's left up to the jury to decide.
05:14Even if it's a match, that'll be just one of many pieces of evidence presented at the
05:18trial.
05:19It takes more than a fingerprint to prove someone's guilty of something.
05:23Like catching them red-handed with your property.
05:28Stop that.