why do we have an appendix

The appendix is believed to serve as a "safe house" for beneficial gut bacteria, helping to restore the gut microbiome after infections or disturbances like antibiotic use. It contains lymphatic tissue that plays a role in immune functions, particularly in early life, aiding the maturation of immune cells and production of antibodies. This helps the immune system manage potential pathogens and maintain local gut immunity. Although the appendix is no longer essential for digestion as in ancestral species, it still contributes to maintaining healthy gut flora and immune defense. The appendix has also been used in reconstructive surgeries as a backup organ. Overall, it is not a useless vestigial organ but has important roles in microbiome regulation and immune function.