The absence of a visible tail in humans can be attributed to evolutionary changes over millions of years. As our early human ancestors transitioned from arboreal to terrestrial lifestyles, the need for a tail for balance and mobility decreased. Natural selection favored individuals with reduced or absent tails, as it provided advantages such as improved bipedal locomotion and freed the hands for tool use and manipulation.
On the other hand, the appendix is a small, finger-like structure attached to the cecum, a pouch at the beginning of the large intestine. While the appendix has long been considered a vestigial organ with no apparent function, recent research suggests that it may play a role in immune function and maintaining the gut microbiome. It's possible that the appendix has retained its presence in humans because it provides some selective advantage in certain circumstances, such as recovering from infections or replenishing beneficial gut bacteria after illness.
Evolution is a complex and dynamic process influenced by a variety of factors, including genetic variations, environmental pressures, and the interplay between different traits and their functions. The loss of the tail and the retention of the appendix in humans reflect the outcomes of these intricate evolutionary forces acting over time.