Fingerprints aren’t unique to people. Our closest relatives, the great apes, have them too, and so does the koala. The koala’s prints, though, come from evolving the same trait separately, not from shared ancestry: humans and koalas have had no common ancestor in over 100 million years.1Medbound Times. Why Do Koalas Have Human-Like Fingerprints? The Evolutionary Mystery Behind Their Striking Similarity to Humans Fingerprints look like a solution nature reached more than once for gripping and feeling, which hints at what they’re for.
The Animals With True Fingerprints
A fingerprint is a pattern of fine raised skin lines, or ridges, with sweat pores along their tops. Chimpanzees have the same three pattern types people do: whorls, loops and arches.2PubMed Central. Grip Preference, Dermatoglyphics, and Hand Use in Captive Chimpanzees (Pan troglodytes) Bonobos have more complex fingertip patterns than common chimpanzees, in the range seen in gorillas.3PubMed. Epidermal patterns of the hands and feet of the pygmy Chimpanzee (Pan paniscus)
Some monkey and ape fingertip ridges are simpler than ours, while the ridges on the pads at the base of their fingers can be more intricate.4Proceedings of the Zoological Society of London. A Comparative Study of the Form and Dermatoglyphs of the Extremities of Primates The resemblance to us comes from inheritance, since apes and humans share a distant ancestor that likely had ridged fingertips. Over time each species’ ridges were shaped by its own way of life, such as knuckle-walking or hanging from branches. That’s why an ape’s fingertip may look familiar but not quite identical to a human one. Apes also have ridges on their palms and soles, just as we do on our hands and feet.
Ridges can show up beyond the hand, too. Spider monkeys and their relatives have a hairless ridged pad on the underside of the tail tip for gripping branches.5PubMed. Mechanoreceptivity of prehensile tail skin varies between ateline and cebine primates Capuchins also grip with their tails, but theirs are fully covered in hair.6PubMed. Mechanoreceptivity of prehensile tail skin varies between ateline and cebine primates
Why Koala Fingerprints Look So Human
Koala fingertip ridges show shapes and patterns strikingly like human prints, such as loops and whorls when viewed up close.7SleuthSayers. Koalas and Crime Scenes The layout is different, though. Koalas have ridges only on their fingertips, while humans have them along whole fingers and palms, so a koala has no palm print comparable to a person’s.8SleuthSayers. Koalas and Crime Scenes The popular story that koala prints have confused crime-scene investigators has no evidence behind it.9Snopes. Are There Documented Cases of Koala Fingerprints Confusing Crime-Scene Investigators?
Koalas evolved prints independently, with unrelated species arriving at the same trait separately.10Medbound Times. Why Do Koalas Have Human-Like Fingerprints? The Evolutionary Mystery Behind Their Striking Similarity to Humans Koalas are marsupials, related to kangaroos rather than apes, and their ancestors lacked fingerprints.
Each front paw has two opposable digits, and koalas grip branches firmly while sleeping and climbing. They also pick and handle leaves with their fingertips. This likely favoured similar skin.
What Fingerprints Actually Do
Ridges and sweat control how the fingertip contacts a surface.11PubMed Central. Finger pad friction and its role in grip and touch When you touch a smooth surface, sweat trapped in the ridges softens the skin and greatly increases friction.12PubMed Central. Fingerprint ridges allow primates to regulate grip Too much water forms a film that lets fingers slide, and the grooves help drain it away. The grooves hold the right amount of moisture whether fingers start wet or dry.13PubMed Central. Fingerprint ridges allow primates to regulate grip This helps primates climb and handle objects in both wet and dry conditions.14PubMed Central. Fingerprint ridges allow primates to regulate grip
Ridges also sharpen touch. Touch nerves in the fingertip can respond to details as small as a single ridge, about 0.4 mm apart.15PubMed Central. Human Touch Receptors Are Sensitive to Spatial Details on the Scale of Single Fingerprint Ridges When a finger slides over a surface, the ridges rub against its tiny bumps and vibrate, at frequencies the deep vibration-sensing nerves detect best.16PubMed. The role of fingerprints in the coding of tactile information probed with a biomimetic sensor Without ridges, the same nerves would get weaker information. In effect, ridges turn fine textures into signals the brain can read.17Wear. Effect of roughness on vibration of human finger during a friction test Uniqueness is a side effect of how prints form; their job is grip and touch.
How Every Fingerprint Becomes One of a Kind
Fingerprint ridges form before birth through a process related to how hair follicles begin.18PubMed. The developmental basis of fingerprint pattern formation and variation Palms and fingertips have no hair, yet the early steps are shared with follicles.
Ridges then spread in waves from different starting spots on each fingertip, and where the waves meet sets the pattern.19PubMed. The developmental basis of fingerprint pattern formation and variation High fingertip pads tend to produce whorls, low pads arches, and in-between pads loops.20PubMed Central. Limb development genes underlie variation in human fingerprint patterns Small differences in fingertip shape make every print unique.
Identical twins show how sensitive this is. They share genes but still have different prints, because small differences in the womb shift the ridge waves. Pattern type can run in families even when the details differ.
Once the ridges form in the deeper layers of skin, they continue to be reproduced as the skin renews itself. A print generally stays the same as a person grows, apart from becoming larger. Minor surface wear or a shallow cut doesn’t change the underlying pattern.
Animals With Grip Pads but Not Fingerprints
Many animal pads are instead smooth, bumpy or cone-textured, so they give grip without forming those lines. Seeing rough texture on a paw isn’t enough to say an animal has fingerprints. Dog and cat pads are rough for traction, but that texture is not a fingerprint.
Raccoons are a good example. They’re known for feeling objects underwater and in the dark, which makes their hands seem humanlike, and their paws carry the same kinds of touch sensors as monkey and human hands.21PubMed. Sensory innervation of the raccoon forepaw: 1. Receptor types in glabrous and hairy skin and deep tissue That explains the sensitivity, but similar sensors aren’t fingerprint ridges, and raccoons lack true fingerprint patterns.
Other mammals vary. Rat paws have pads in positions similar to ours, and some show ridge patterns.22PubMed. Palmar and plantar pads and flexion creases of the rat (Rattus norvegicus) A climbing dormouse has ridged pad skin with twice the sweat gland density of a harvest mouse’s cone-textured pads.23Journal of Zoology. A comparison of the gross morphology and micro-anatomy of the foot pads in two fossorial and two climbing rodents (Mammalia) River otter paw pads are over 10 times softer than human skin, with grooves about as deep as fingerprints but running in different directions.24PubMed Central. Enhanced wet grip with North American river otter paws Some bats grip smooth leaves with thumb pads using suction, dry stickiness or glue.25Journal of Mammalogy. Adhesive Devices on the Thumb of Vespertilionoid Bats (Chiroptera)
Beyond mammals, tree frog toe pads are made of six-sided cells divided by mucus-filled channels.26PubMed Central. Wet but not slippery: boundary friction in tree frog adhesive toe pads They keep a very thin fluid layer that lets the frog cling without slipping.27PubMed Central. Ultrastructure and physical properties of an adhesive surface, the toe pad epithelium of the tree frog, Litoria caerulea White These pads use mucus channels, not sweat ridges.
Noseprints in Cows and Dogs
A cow’s nose carries ridges and beads that can be inked onto glossy paper like a fingerprint.28PubMed Central. Identification of Cattle Using Nasolabial Plate Imprints and Biometric Analysis The result is often called a noseprint. Each ridge or bead can end, split or begin at a particular spot, and these detail points are what get compared. Matching enough of them can tell one animal from others.29PubMed Central. Identification of Cattle Using Nasolabial Plate Imprints and Biometric Analysis
Computer systems can match cattle nose photos correctly about 96% of the time.30Pattern Recognition. The muzzle as a biometric feature: Cattle identification using unique muzzle patterns Photos are easier to collect than inked prints, which is the appeal.
Dog nose patterns are being developed as an alternative to microchips and tags.31Applied Sciences. Dog Identification Method Based on Muzzle Pattern Image The approach is still developing, so keep a microchip for now.