Male Nipples
Male nipples are sometimes referred to as vestigial, although they aren’t truly, because they were never functional in our ancestors. Instead, they most likely occur because in the embryonic stage we are essentially sexless, only differentiating into male and female with the presence of hormones.
Goose Bumps
When we get goose bumps, it’s the action of muscle fibers called erector pili, which cause the hairs in follicles to stand to attention. In animals, such as a cat, this causes a larger appearance and can be used to thwart an attacker, as well as trap air between feathers and fur for insulation. However, humans, with our minimal coating of fur, don’t really need the raised hair; we use jackets instead. It is therefore thought that goose bumps don’t really serve much of a purpose. However, the small expenditure of energy used to contract the muscles could, perhaps, cause a tiny release of heat. Or, because goose bumps are associated not only with cold, but emotional responses as well (listening to a good song, seeing a scary movie) they could now serve as a form of communication with others.
Vomeronasal Organs (VNOs)
In mice and other animals, the tiny vomeronasal organs (VNOs) are thought to be responsible for pheromone detection, helping to pick up the chemicals that signal a potential mate, reproductive status, and other social cues. Although similar structures have been found in humans, they’re largely thought to be vestigial and inactive, having lost nerve connection to the brain.
There are other vestigial and atavistic structures in humans, especially when you consider the potential leftovers in our genomes. And if they don’t require too much energy or resources to make, chances are they’ll stick with us for the long haul.
Image sources: Ildar Sagdejev (cc), National Institutes of Health, History of Medicine.
