1. Why are the muscles that make hair stand up vestigial?
2. what are the probable functions of the muscles that makes hair stand up?
1. The muscles that make hair stand up, known as the arrector pili muscles, are considered vestigial because they no longer serve their original purpose in humans. Vestigial traits are remnants of structures or functions that were present in ancestors but are now reduced or obsolete in the current species.
In our evolutionary past, when humans had more hair and thicker body fur, the contraction of the arrector pili muscles would cause the hair to stand up, which would trap a layer of air near the skin. This trapped layer of air would provide insulation, keeping the body warm and aiding in protecting against the cold. However, as humans evolved and lost body hair, the need for this insulating mechanism diminished, rendering the arrector pili muscles vestigial in our species.
2. While the arrector pili muscles are vestigial in humans, they still have some minor functions. These functions are believed to include:
- Producing piloerection: The muscles can still contract to give the appearance of "goosebumps" or "chicken skin" when we experience strong emotions like fear or excitement. This response is a remnant of the fight-or-flight response found in our evolutionary ancestors.
- Facilitating oil secretion: The contraction of these muscles can help express sebum (oil) from the hair follicles onto the skin. Sebum provides some moisture and protection to the hair and skin.
- Aiding tactile senses: When the arrector pili muscles contract, they can cause the hair follicles to pull on nerve endings, providing a heightened sense of touch or awareness of the surrounding environment. This could have been beneficial for detecting sensory information in our ancestral past.
In summary, while the arrector pili muscles are considered vestigial in humans because they no longer serve their primary function, they still have some secondary roles that are thought to be remnants of their original purpose in our evolutionary history.