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Taste receptors are responsible for taste perception, and in humans lineage-specific pseudogenization of bitter taste receptor has occurred; this pseudogenization of bitter taste receptors may also be occurring in non-human primate lineages, but the rate at which it is occurring in the human lineage is significantly higher. Likewise, one study has found that two bitter taste receptor genes in the human lineage have undergone fixed pseudogenization, and that none have done so in the chimpanzee lineage.
Human Lineage-specific Gene Inactivation, , Encyclopedia of Life Sciences: Evolution and Diversity of Life, p.1-8, (2005)
Lineage-specific loss of function of bitter taste receptor genes in humans and nonhuman primates., , Genetics, 2005 May, Volume 170, Issue 1, p.313-26, (2005)