Scan of the left hand of a 10-week-old human embryo. The dorsometacarpales are highlighted: these muscles are present in adults of many other limbed animals, while in humans they normally disappear or become fused with other muscles before birth. Image via Rui Diogo, Natalia Siomava and Yorick Gitton.
New research shows that some muscles, thought to have been abandoned by our mammalian ancestors 250 million years ago, never completely went away.
A team of evolutionary biologists have demonstrated that numerous atavistic limb muscles – remnants of anatomy that evolution never completely ditched – are actually formed during early human development and then lost prior to birth. According to the study, published October 1, 2019, in the journal Development, they are probably among the oldest, albeit fleeting, remnants of evolution yet seen in humans.
Some of these muscles, such as the dorsometacarpales shown in the image above, disappeared from our adult ancestors more than 250 million years ago – a relic from when reptiles transitioned to mammals. The scientists aren’t sure why the human body makes and then deletes them before birth.
Evolutionary biologist Rui Diogo of Howard University led the study. Diogo told the BBC:
Why are they there? Probably, we cannot just say in evolution, ‘Look, I will delete from scratch, from day zero, the muscle going to digits two, three, four, five and I will just keep the one going to the thumb.’
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According to a statement from the researchers about the study:
Remarkably, in both the hand and the foot, of the 30 muscles formed at about 7 weeks of gestation one third will become fused or completely absent by about 13 weeks of gestation. This dramatic decrease parallels what happened in evolution and deconstructs the myth that in both our evolution and prenatal development we tend to become more complex, with more anatomical structures such as muscles being continuously formed by the splitting of earlier muscles.
For the study, the team scanned the tissues of more than a dozen embryos and young fetuses in high-res 3D over a number of weeks. They found tiny muscles in the hands and feet in 7-week-olds that were no longer visible by week 13. The unprecedented resolution offered by the 3D images revealed the transient presence of several of such atavistic muscles, Diogo said in a statement.
It used to be that we had more understanding of the early development of fishes, frogs, chicken and mice than in our own species, but these new techniques allow us to see human development in much greater detail.
He added:
Interestingly, some of the atavistic muscles are found on rare occasions in adults, either as anatomical variations without any noticeable effect for the healthy individual, or as the result of congenital malformations. This reinforces the idea that both muscle variations and pathologies can be related to delayed or arrested embryonic development
Bottom line: Ancient reptilian “hand” muscles have been found in human embryos.
from EarthSky https://ift.tt/3225XkJ
Scan of the left hand of a 10-week-old human embryo. The dorsometacarpales are highlighted: these muscles are present in adults of many other limbed animals, while in humans they normally disappear or become fused with other muscles before birth. Image via Rui Diogo, Natalia Siomava and Yorick Gitton.
New research shows that some muscles, thought to have been abandoned by our mammalian ancestors 250 million years ago, never completely went away.
A team of evolutionary biologists have demonstrated that numerous atavistic limb muscles – remnants of anatomy that evolution never completely ditched – are actually formed during early human development and then lost prior to birth. According to the study, published October 1, 2019, in the journal Development, they are probably among the oldest, albeit fleeting, remnants of evolution yet seen in humans.
Some of these muscles, such as the dorsometacarpales shown in the image above, disappeared from our adult ancestors more than 250 million years ago – a relic from when reptiles transitioned to mammals. The scientists aren’t sure why the human body makes and then deletes them before birth.
Evolutionary biologist Rui Diogo of Howard University led the study. Diogo told the BBC:
Why are they there? Probably, we cannot just say in evolution, ‘Look, I will delete from scratch, from day zero, the muscle going to digits two, three, four, five and I will just keep the one going to the thumb.’
EarthSky’s 2020 lunar calendars are here! Get yours today. They make great gifts. Going fast.
According to a statement from the researchers about the study:
Remarkably, in both the hand and the foot, of the 30 muscles formed at about 7 weeks of gestation one third will become fused or completely absent by about 13 weeks of gestation. This dramatic decrease parallels what happened in evolution and deconstructs the myth that in both our evolution and prenatal development we tend to become more complex, with more anatomical structures such as muscles being continuously formed by the splitting of earlier muscles.
For the study, the team scanned the tissues of more than a dozen embryos and young fetuses in high-res 3D over a number of weeks. They found tiny muscles in the hands and feet in 7-week-olds that were no longer visible by week 13. The unprecedented resolution offered by the 3D images revealed the transient presence of several of such atavistic muscles, Diogo said in a statement.
It used to be that we had more understanding of the early development of fishes, frogs, chicken and mice than in our own species, but these new techniques allow us to see human development in much greater detail.
He added:
Interestingly, some of the atavistic muscles are found on rare occasions in adults, either as anatomical variations without any noticeable effect for the healthy individual, or as the result of congenital malformations. This reinforces the idea that both muscle variations and pathologies can be related to delayed or arrested embryonic development
Bottom line: Ancient reptilian “hand” muscles have been found in human embryos.
from EarthSky https://ift.tt/3225XkJ
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