A team of researchers has discovered that several muscles tend to develop and disappear in human fetuses. The latter phenomenon takes place before birth, and it comes as a surprise for many researchers as some of the muscles haven’t been encountered in over 250 million years when some of our ancestors roamed the Earth.
It is well-known that the evolutionary process tends to offer some traits which are no longer relevant. Among humans the appendix and wisdom teeth are prime examples. A large number of animals will develop body parts during pregnancy. The traits tend to lessen or disappear completely before birth.
During the elaboration of the new study, the researchers employed advanced 3D imaging tools to obtain in-depth scans of specific body parts. This allowed them to capture impressive images which are also quite surprising.
For example, they observed 30 individual muscles in hand and foot of a seven-week-old fetus. Images taken during week 13 reveal that more than 30% of the muscles disappeared or fused with other muscles. Dorsometacarpales are a pair of atavistic muscles that can be found across many animals, including lizards how salamanders. However, they were last seen in humans in the case of adult ancestors who lived 250 million years ago.
A large selection of the muscles which have been observed during the study has not been featured in works that focus on human prenatal development. The window of development is also quite late when atavisms are involved.
By observing this type of organs and body parts, researchers can learn more about how evolution works over a long period. Even if we no longer need a tailbone, the information is present within the DNA, and one will form and vanish before we are born. In some cases rare mutations can make these traits permanent.
The study has been published in a scientific journal.