Buzz
For thousands of years, humans have questioned the purpose of seemingly functionless physical traits in living beings. However, it was during the late 18th and early 19th centuries that the concept of vestigiality gained prominence through the works of French naturalists and early evolutionary thinkers, Étienne Geoffroy Saint-Hilaire and Jean-Baptiste Lamarck. While Charles Darwin revolutionized human biology with On the Origin of Species, it was his 1871 publication, The Descent of Man, that first identified several structures now recognized as vestigial, such as the appendix, tailbone, and wisdom teeth.
The term was formally introduced by German anatomist Robert Wiedersheim in his 1893 book The Structure of Man: An Index to His Past History, which listed 86 organs considered remnants of human evolution. While some organs on Wiedersheim’s list, like the thymus and pituitary gland, are now known to be essential, others have been replaced by newly identified vestigial traits. Below are six intriguing examples of human vestigiality.
1. GOOSE BUMPS
Medically termed cutis anserina, goose bumps (named for their similarity to the skin of a plucked goose) are an involuntary reaction to various stimuli such as fear, pleasure, awe, nostalgia, and cold. This response, known as piloerection, occurs when the small muscles at the base of each hair contract, forming tiny bumps. In our evolutionary past, this reflex was vital for the fight-or-flight response of our hair-covered ancestors. The raised hairs made them appear larger to predators, potentially deterring attacks. In cold conditions, goose bumps provided additional insulation by trapping warmth. While many animals still use piloerection as a defense mechanism (like an agitated porcupine or a cornered cat), humans, having lost most of their body hair, now experience it primarily as an emotional reaction.
2. JUNK DNA
This term describes sections of the human genome with no known function. While controversial, many researchers argue that much of our DNA consists of remnants from evolutionary processes. Within our DNA sequences, there are traces of genetic fragments such as pseudogenes and transposons, which suggest past mutations caused by viruses or other evolutionary changes. Like other vestigial structures, these genetic remnants persist because they cause no harm, being copied and passed down through generations despite their apparent lack of purpose.
3. PLICA SEMILUNARIS
This small fold of tissue in the eye’s corner is a remnant of the nictitating membrane, a third eyelid that once served a functional role. Found in birds, reptiles, and fish, this membrane is translucent and slides across the eye to protect and moisten it while maintaining vision. Although humans no longer need this feature, a small portion remains, along with its associated muscles. The plica semilunaris is more prominent in certain ethnic groups, particularly Africans and Indigenous Australians.
4. MUSCLES
As human evolution has reduced our reliance on physical strength, several muscles in the body have become largely unnecessary, though many people still retain them. The prevalence of these vestigial muscles often varies by ethnicity. For instance, the occipitalis minor, a slender muscle at the skull's base responsible for scalp movement, is present in all Malays, half of the Japanese population, and a third of Europeans, but is entirely absent in Melanesians. Connected to the auricular muscles, which once enabled ear movement to detect predators, these muscles are now mostly nonfunctional.
Other examples of vestigial muscles include the palmaris longus, a tendon in the wrist that tightens when the hand is clenched; the pyramidalis in the abdomen, missing in 20 percent of humans; and the plantaris in the leg, which minimally assists in knee flexion. Its role is so insignificant that it is often harvested by surgeons for use in grafts to repair injuries elsewhere in the body.
5. PALMAR GRASP REFLEX
One of the most noticeable behaviors in infants is their ability to tightly grip a finger placed in their hand (early research highlighted the surprising strength of this reflex). While this action is often seen as a bonding gesture, it is actually an evolutionary response. In our hair-covered ancestors, this reflex allowed babies to cling to their mother’s fur, ensuring they could be carried easily and leaving the mother’s hands free to escape danger, such as climbing a tree. This reflex is also present in the feet, evident when an infant’s toes curl, but both the hand and foot reflexes typically fade by six months of age.
6. OLFACTION
Our sense of smell can be considered somewhat vestigial. While we still use it daily, its importance has significantly diminished compared to its role in the past. Animals with highly developed olfactory senses rely on them for finding food, evading predators, and mating. In contrast, humans, with access to grocery stores, no natural predators, and dating platforms like OkCupid, now view smell more as a convenience (though research suggests pheromones may influence human interactions). Unlike other vestigial traits, the ability to smell can still be crucial for survival, such as detecting invisible dangers like gas leaks.
