How do vestigial organs show ancestral relationships?

Answer 1

Vestigial organs are often used as evidence to argue in favor of Darwinian evolution. These organs are allegedly left over from our ancestors but are no longer useful or needed. Evolution proponents typically contend that such structures are best explained as remnants of evolutionary history. Supposedly, the best explanation for these non-functional traits is that they once served a purpose in our ancestor but now no longer do. There are 5 organs we do not need: The vomeronasal organ (VNO) is a pair of pit-like structures in the upper part of the inside of the nose. In many mammals, this is a sensory organ that is used to detect pheromones (chemical signals that trigger behavioral responses such as reproductive responses). While the chemosensory role of this organ is fairly well established in mammals such as mice, the exact function for humans has been more elusive. While it is expected to serve a sensory function, it appears to lack neurons that connect it to the brain. The second vestigial organ is goosebumps. In many animals, this reflex that causes hair to stand erect is used to generate warmth. It can also make the animal appear larger as happens when a cat's fur stands on end when it is frightened. Goosebumps are a natural response to cold or high emotions. There is nothing really wrong or dysfunctional about the small erector pilli muscles that cause the bulge of skin as the hair stands erect. The classification of goosebumps as a vestigial organ stems from a revised definition of vestigial. A vestigial organ does not necessarily have to be completely functionless. If an organ or response is reduced compared to its ancestral version or takes a slightly different form, it can be considered vestigial. Under the revised definition, because human hair is "puny" and the thermoregulatory impact reduced, goosebumps can be considered vestigial. The third organ on the list requires tortured logic to be considered vestigial. Darwin's point is "thought to be a vestige of a joint that allowed the top part of the ancestral ear to swivel or flop down over the opening of the ear." Actually, it is a harmless congenital defect that results from a malformation as the ear folds during early development. Darwin's point is found in about 10% of humans. Its vestigial status is the observation that it is inherited as an autosomal dominant trait. Autosomal dominant traits will be expressed if an individual inherits the gene from even one parent. Since Darwin's point is a dominant trait this is supposed to imply that it was useful. Additionally, it shows incomplete penetration which means that not all individuals that have the gene will express the trait. The incomplete penetration is supposed to mean that it has since lost its functional role. The tailbone or coccyx has often been presumed to be vestigial and a leftover remnant to our alleged mammal and reptilian ancestors who also had tails. Evidence that is cited includes the variable number of bony segments humans can have (usually 4 but can be 3 or 5) as well as "babies born with tails." But these so called tails are not really tails at all and instead are a type of fatty tumor. There are no bones or muscles in them at all, and thus, it cannot truly be considered a vestigial organ. The last vestigial organ on the list are the wisdom teeth. This is a third set of molars that erupt last. Because of crowding, the wisdom teeth often become impacted and must be removed to avoid complications. Nonetheless there are many people whose wisdom teeth erupt without incident. For those who must have the wisdom teeth pulled, there is little loss. About 35% of people do not develop wisdom teeth. This is an example of a loss of information.