"`` Six pairs of these aortic arches loop over the pharynx . In primitive fish , these arches persist and enable the gills to oxygenate the blood . In adult birds and mammals , in which lungs oxygenate the blood , such a system makes little sense - but all six pairs of aortic arches are formed in mammalian and avian embryos before the system eventually becomes simplified into a single aortic arch . Thus , even though our physiology does not require such a structure , our embryonic condition reflects our evolutionary history. `` ( Developmental Biology : Seventh Edition , Scott F. Gilbert , Sinauer Associates Inc. , 2003 , p500 )"
"Another characteristic in this same general area that ties us back to fish is the development of our parathyroid glands - which are very similar to gill buds in fish - from a particular pharyngeal arch : the same one that in fish gives rise to the gill buds ! Moving on to the kidneys for a minute . The human embryo forms not one , but 3 successive kidneys : the pronephric , mesonephric , and metanephric kidneys . Only that last one persists and only it is the kidney you and I and all of our fellow humans use . Why do human embryos go through two transient and simpler kidneys before getting it right ? Here 's a hint : the other two are carry overs from simpler organisms ! The evolutionarily simplest vertebrates , such as hagfish and teleost fish , develop only the pronephric kidney : it is their adult functional kidney . Now move up an evolutionary notch to ( other ) fish and amphibians . In their embryos , the first kidney still develops , but soon begins to degenerate and is replaced by the mesonephric kidney , which is the functional adult kidney in these organisms . Now move up another evolutionary notch , to reptiles , birds , and mammals . Their embryos form the first kidney , which then degenerates and is replaced by the second kidney , which then degenerates and is replaced by the final , metanephric kidney : their adult functional kidney . The above is not anywhere near a complete list of embryological evidences for common descent/evolution . PS : Note the serial addition of developmental stages that occurs in kidneys as one moves up to higher evolutionary levels : `` ontogeny recapitulates phylogeny `` . Of course this `` law `` does not hold for all organs/organ systems in all organisms , but it does hold for a few cases . And that 's enough to clearly indicate evolution of those organ systems by their being retained from ancestors and then modified during embryonic development ."
"In primitive fish , these arches persist and enable the gills to oxygenate the blood"
"which are very similar to gill buds in fish - from a particular pharyngeal arch"