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In Neil Shubin's book, Your Inner Fish: A Journey into the 3.5 Billion Year History of the Human Body, he asserts that embryology demonstrates that every head on every animal from a human to a shark shares four developmental arches. These arches are best described as swellings or indentations loaded with genes that turn on and off and instruct cells to design a head. In fish these arches develop into gills. In humans, the first arch forms the jaws, two small ear bones,the malleus and incus, and all the blood vessels and muscles that run to them. The second arch forms another ear bone, the stapes, a small throat bone, and many muscles that are responsible for facial movement and expressions. The third arch forms muscles, nerves, and bones used for swallowing. The fourth arch forms the larynx and related parts. Pretty amazing research!
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