Q: How can the branchial arches provide evidence to common ancestry?
- The head is one of the most substantial parts of the human
body, as it houses the brain. It might be astonishing to realize that the
human's head and a shark's gill originate from the same pieces of an embryo. Every
vertebrate animal starts with these four arches known branchial arches, having
the same shape. They are labeled as 1, 2, 3 and 4.
- In humans, the first arch develops into the upper and
lower jaw, the malleus and incus bones in the inner ear, and the blood vessels
and muscle that attach to them. The
second arch turns into the third ear bone (stapes), a bone in the throat, and
the muscles that control facial expressions.
The third arch forms the muscles, bones, and nerves of the throat
(swallowing). The fourth arch forms the
larynx and other parts deep in the throat.
- Whereas in sharks the branchial arches develop into the
different features. The first arch becomes the jaw, same as us. The second arch in sharks becomes a bar of
cartilage and muscle. In humans that bar
breaks up to become the stapes and some small structures of the throat. In the shark, the bar becomes the structure
that allows sharks to extend their jaw slightly out of their mouth while
feeding. The bone that allows this in
sharks, if you carefully trace its evolutionary history becomes our stapes.
- Humans sometimes get ruptured disks in our
spines. Those disks are a holdover from
Amphioxus, a worm. A non-vertebrate that
does have a notocord and gill slits, the precursors of our own spine and allowing
to speak
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