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Humans ' outerearsmay have evolved from the gill of prehistorical fish , a new study finds .
cistron - redaction experiments indicate that cartilage in fish gills transmigrate into the ear epithelial duct zillion of years ago during the course of ourevolution . pass even further back , our outer ear may have evolutionary roots in ancient marine invertebrates , such ashorseshoe crabs , scientists say .
The human outer ear may have arisen from ancient fish gills.
The research sheds fresh lighter on the mysterious extraction of out spike , which are unique to mammalian . " When we started the project , the evolutionary origin of the out ear was a everlasting black box , " study carbon monoxide gas - authorGage Crump , a professor of prow cubicle biology and regenerative medicine at the University of Southern California , enunciate in astatement .
Researchers already have sex that our middle ears — each of which sits behind the eardrum and contain three small bones — arose from the jawbonesof ancient fish . This example of evolution transforming and repurposing anatomical body structure " made us wonder whether the cartilaginous outer capitulum may also have arisen from some ancestral fish structure , " Crump said .
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A gene control element for human outer ear development shows activity in the gills (green) of a zebrafish.
Our out ears and those of other mammalian are made of a subtype of cartilage called pliable cartilage . It is more whippy than either hyaline cartilage or fibrocartilage , which are present in the human nozzle and in the disks between our vertebrae , severally .
The key to trace the origins of humans ' out ears to fish was the breakthrough that pliable gristle is also present in Pisces branchia . " When we started the sketch , there was very small out there about whether elastic cartilage existed out of doors of mammals , " Crump said .
The researchers used protein grease to reveal that the gill of zebrafish ( Danio rerio ) , Atlantic salmon ( Salmo salar ) and three other coinage of fish contain pliant cartilage . The species are all modern bony Fish , suggesting that flexible gristle is a general feature in this group , fit in to the study , which was published Jan. 9 in the journalNature .
Next , the scientists tested the evolutionary link between elastic gristle in Pisces gill and mammalian outer ears . flexible gristle does n’t carry on well in fossil , so the researchers used molecular clues instead . They looked for gene control chemical element called " enhancers " — shortsighted DNA sequences that can activate associated factor when bound by specific proteins .
Because genetic foil are highly tissue - specific , researchers can easy find where the foil are active . To test whether enhancer natural process — and therefore gene regularization — is similar in Pisces the Fishes gill and human out ear , Crump and his fellow slip in human outer pinna enhancer into zebrafish genome .
The experimentation triggered bodily process in the gills of zebrafish , hinting at an ancestral link between the genes in human outer ear and Pisces the Fishes gill . Then , the researchers conducted the experiment in reversal : They insert enhancer relate with zebrafish gills into mouse genomes and discover activity in the mouse ’s out auricle .
Through another series of experiments with tadpoles and green anole lizard ( Anolis carolinensis ) , the squad show that amphibians and reptiles also inherit their branchia and auricle structures from fish . In lizards , enhancer activity was in the auricle epithelial duct , which propose that pliable gristle had begin migrating from the gills to the KO’d ear by the time reptiles appeared on Earth around 315 million years ago .
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" Our findings suggest that elements of an ancestral gill developmental platform were reutilized multiple time through the track of vertebrate evolution to generate various branchia and capitulum structure , " the investigator write in the field of study .
Finally , the squad found an enhancer in horseshoe Cancer the Crab cellphone that triggered activity in zebrafish gills . Horseshoe crabs are " living fossil " that issue around 400 million class ago , and the discovery paint a picture our outer spike may have much deep evolutionary roots than previously think .
Although more research is require to affirm how deep these roots stretch , " this work provide a new chapter to the evolution of the mammalian capitulum , " Crump said .
