Embryonic rudiments that never fully develop, such as the gill slits in humans, are common in all sorts of animals. Some, however, like the tail rudiment in humans, persist as adult vestiges reflecting evolutionary ancestry. The most familiar rudimentary organ in humans is the vermiform appendix. This wormlike structure attaches to a short section of intestine called the cecum, which is located at the point where the large and small intestines join. The human vermiform appendix is a functionless vestige of a fully developed organ present in other mammals, such as the rabbit and other herbivores, where a large cecum and appendix store vegetable cellulose to enable its digestion with the help of bacteria.
Organic evolution refers to changes in populations.
It is influenced by both genetics and environment. All organisms go through changes in appearance during their lifespan. This is called ontogeny . In each of these examples, no genetic change is involved. The genotype remains the same, but the phenotype varies dramatically .