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In humans, the vermiform appendix is sometimes called a vestigial structure as it has lost much of its ancestral digestive function.. Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. [1]
Ileum, caecum and colon of rabbit, showing Appendix vermiformis on fully functional caecum The human vermiform appendix on the vestigial caecum. The appendix was once believed to be a vestige of a redundant organ that in ancestral species had digestive functions, much as it still does in extant species in which intestinal flora hydrolyze cellulose and similar indigestible plant materials. [10]
This phenomenon is an automatic-response mechanism that activates even before a human becomes consciously aware that a startling, unexpected or unknown sound has been "heard". [2] That this vestigial response occurs even before becoming consciously aware of a startling noise would explain why the function of ear-perking had evolved in animals.
Atavism can also be seen in humans who possess large teeth, like those of other primates. [9] In addition, a case of "snake heart", the presence of "coronary circulation and myocardial architecture [that closely] resemble those of the reptilian heart", has also been reported in medical literature. [ 10 ]
The formation of goose bumps in humans under stress is considered by some to be a vestigial reflex, [4] though visible piloerection is associated with changes in skin temperature in humans. [5] The reflex of producing goose bumps is known as piloerection or the pilomotor reflex , or, more traditionally, [ 6 ] horripilation .
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The last common ancestor between humans and other apes possibly had a similar method of locomotion. 12-8 Ma The clade currently represented by humans and the genus Pan (chimpanzees and bonobos) splits from the ancestors of the gorillas between c. 12 to 8 Ma. [31] 8-6 Ma Sahelanthropus tchadensis