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Human fetuses develop lizard-like body parts that disappear before birth



Photo: Alberta Government (Flickr (CC BY 1.0))

New research this week seems to show that human fetuses develop more Muscles in legs and arms disappear when they are born. And some of these muscles were last seen by our adult ancestors over 250 million years ago.

The evolutionary journey of a species is littered with detours and dead ends. Humans, for example, have remnants of parts of the body that used to function, but are practically unusable today (the appendix is ​​usually found to be remnants of organs, though a better example might be our wisdom teeth). Many animals also develop early in development body parts that largely or completely fade before birth, such as the human coccyx to track the formation of these temporary human body parts in full detail. Using advanced 3D imaging techniques, the authors claimed to be able to map the earliest growth of our limbs – and it's pretty crazy.

The dorsal view of the left hand of a 10-week-old human embryo, with highlighted dorsometacarpales.
Image: Rui Diogo, Natalia Siomava and Yorick Gitton (Development)

In So, for example, they found 30 single muscles on the hand and foot of a seven-week-old fetus. But by the 13th week of pregnancy, a third of the muscles had disappeared or fused. A pair of these atavistic muscles, as they are called, are called Dorsometacarpales. And although it still occurs in many living animals such as lizards and salamanders, it does not seem to exist in our adult ancestors 250 million years ago.

"Fascinating is that we've seen different muscles that have never been described. Human prenatal development and some of these atavistic muscles have been observed even in 11.5-week-old fetuses, which is surprisingly late for developmental cancers," study author said Rui Diogo, evolutionary biologist at Howard University in Washington, DC, in a press release from the publishers of the study.

These remaining organs and parts are a neat example of how evolution works over a long period of time. We may not need a tail anymore, but our genome still has the blueprint for it. And they can even reappear if someone with a rare mutation is born or if something happens in the womb that interferes with their development.

Although these muscles would probably do little harm to them at birth, the authors say their research confirms that such abnormalities and anomalies can be caused by the delayed or delayed development of a fetus in the womb. And perhaps most of all, according to Diogo, the results provide "a fascinating and effective example of evolution in the game".


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