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    HomeScienceDNA Discovery Unlocks Secret to How Humans Lost Their Tails

    DNA Discovery Unlocks Secret to How Humans Lost Their Tails

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    Portrait of a chimpanzee
    Portrait of a chimpanzee

    The question of how humans and apes lost their tails has confounded scientists for generations. Now, a recent study, published on February 28th in the prestigious journal Nature, has revealed a genetic breakthrough explaining this long-standing mystery.

    closeup of a western gorilla, critically endangered animal specie from Africa
    closeup of a western gorilla, critically endangered animal specie from Africa

    By comparing the DNA of tail-less apes and humans with tailed monkeys, researchers identified a specific DNA insertion that played a pivotal role in the evolutionary loss of tails in primates.

    Big female gorilla in a Zoo Zurich
    Big female gorilla in a Zoo Zurich

    The investigation centered around a gene known as TBXT, which had been previously linked to tail development in vertebrates. More than 100 genes had been associated with tail growth, but this latest study found that it wasn’t mutations within TBXT itself that were responsible.

    Portrait of a Common Chimpanzee in the wild, Africa.
    Portrait of a Common Chimpanzee in the wild, Africa.

    Instead, it was the insertion of a particular DNA segment, known as AluY, into the gene’s regulatory code that had the profound effect.

    Wild Baby Orangutan Eating Red Berries in The Forest Of Borneo Malaysia
    Wild Baby Orangutan Eating Red Berries in The Forest Of Borneo Malaysia

    AluY belongs to a group of genetic elements referred to as “jumping genes” or retrotransposons, which can insert themselves into various places within the genome.

    Moody looking Gorilla
    Moody looking Gorilla

    While typically dismissed as ‘junk’, these sequences have shown to play roles in genetic diversity and evolution.

    Thinking Gorilla
    Thinking Gorilla

    The research team, led by then-student Bo Xia, demonstrated that this AluY insertion within TBXT affected the gene’s RNA splicing, leading to the production of different forms of TBXT RNA and, consequently, a variety of tail lengths in mice engineered to carry the mutation.

    Portrait of very powerful but calm alpha male African gorilla
    Portrait of very powerful but calm alpha male African gorilla

    “This finding is remarkable because most human introns carry copies of repetitive, jumping DNAs without any effect on gene expression, but this particular AluY insertion did something as obvious as determine tail length,” explained study co-author Jef D. Boeke.

    Orangutans are great apes with long arms and reddish hair, endemic to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China
    Orangutans are great apes with long arms and reddish hair, endemic to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China

    The research also showed that the AluY element is present in great apes, including humans, but is absent in monkeys.

    Orangutan Asian species of extant great apes
    Orangutan Asian species of extant great apes

    Notably, the study suggests a profound evolutionary advantage for tail loss, potentially linked to bipedalism and life on the ground, despite the possibility of detrimental side effects.

    Orangutan, Borneo, Indonesia. Native to Indonesia, Malaysia, they are found in only the rainforests of Borneo, Sumatra. They are most arboreal of great apes, spend most of their time in trees
    Orangutan, Borneo, Indonesia. Native to Indonesia, Malaysia, they are found in only the rainforests of Borneo, Sumatra. They are most arboreal of great apes, spend most of their time in trees

    Indeed, the insertion was associated with a slight increase in neural tube defects in mice, reminiscent of conditions like spina bifida seen in human neonates.

    Orangutan, Pongo pygmaeus, Sekonyer River, Tanjung Puting National Park, Kalimantan, Borneo, Indonesia
    Orangutan, Pongo pygmaeus, Sekonyer River, Tanjung Puting National Park, Kalimantan, Borneo, Indonesia

    The research team, which includes experts from NYU Grossman School of Medicine and the Broad Institute of MIT and Harvard, hopes to further explore the theory that tail loss in our ancestors may have contributed to the occurrence of these neural tube defects.

    Infant orangutan with mother
    Infant orangutan with mother

    The insights from this study pave the way for a deeper understanding of the genetic basis of tail loss in humans and apes and could influence broader genomic analysis in the future.

    Orangutan, Pongo pygmaeus, Tanjung Puting National Park, Borneo, Indonesia
    Orangutan, Pongo pygmaeus, Tanjung Puting National Park, Borneo, Indonesia

    This breakthrough not only illustrates the intricate ways in which genetic elements can drive evolutionary changes but also underscores the complexity and adaptability of the human genome.

    Mother and baby orangutan play on ropes
    Mother and baby orangutan play on ropes

    It highlights the shifting perspective on ‘junk DNA’ from genomic clutter to key evolutionary players, shaping our understanding of the processes that have crafted the human species as we know it today.

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