Shubin says that "we're all modified sharks." He compares the arches and swellings during development of sharks and humans, pointing out the 4 arches that both have in common. According to Shubin, "the richness of the story lies in what happens inside each arch."
What do these four arches develop into in humans? What do these similarities in arches tell us about humans and how we have evolved from sharks? What other similarities exist between sharks and humans? What conditions may have led to selective advantages that humans now have?
Hannah Kay (hgkay@aol.com)
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ReplyDeleteThe first arch in both sharks and humans forms into the jaw, but in humans it also forms some ear bones. The cells of the second arch divide and change into a bar of cartilage and muscle. In a shark, this forms two bones that supports the upper and lower jaws. In humans, it becomes three bones in our middle ear. One of which compares to the lower jaw bone of the shark and assists us in swallowing(hyoid). Human bones that allow us to swallow and hear are similar to the bones in sharks that support their upper and lower jaws. For sharks the third and fourth arch are parts of tissues that support the gills. However in humans these structures help us to talk and swallow.
ReplyDeleteUsing molecular tests, researchers at the University of Florida found two independent genetic markers of neural crest cells in the sharks' electroreceptors. Neural crest cells are embryonic cells that pinch off early in development to form a variety of structures. In humans, these cells contribute to the formation of facial bones and teeth, among other things. Researchers found that about a dozen genes that help give rise to a shark's median fins also determine where paired side fins will form on its body. These genes are known to play important roles in the development of paired limbs in humans and other land animals.
"A common feature between the elephant sharks, other sharks and humans is that in all, the fertilization occurs internally, whereas in teleost fishes, fertilization occurs externally". (http://www.digitaljournal.com/article/190214#ixzz1IVHKQfd7). Many genes compare similarly between sharks and humans involved in the production of sperm. Both species produce sperm that appears to have receptors on the tip that allow fusing with a female egg. Other bony fishes’ sperm enter eggs via a pore called micropyle, which both sharks and humans lack. Also it has been researched that the immune systems in both sharks and humans are very similar. Sharks have all four types of blood cells that mammals have.
-Adnan Jahan
(adnanjahan@gmail.com)
I agree with what Adnan said about what the arches develop into in humans and sharks: the first forms the jaw, the second gives rise to a bar of cartilage and muscle, and the third and fourth arches help humans to talk and swallow and the gills in sharks to be supported (91). I also agree with the similarities Adnan found between sharks and humans. Another similarity found between sharks and humans is their genes. At least one shark species has been found to possess several genes that are nearly identical to those in humans. Researchers at the Institute of Molecular and Cell Biology in Singapore identified 154 genes in humans that match comparably with mice, dogs, and elephant sharks. The scientists understood the similarities between humans and mice and humans and dogs, but were shocked to see the similarities between humans and sharks. Also, there are many similarities between the cranial nerves of sharks and humans. “Virtually all of our nerves are present in sharks” (92). The trigeminal, facial, glossopharyngeal, and vagus nerves in both sharks and humans supply similar structures and they exit the brain in the same order. However, sharks and humans are not exactly the same. One advantage that is seen in sharks is that they are believed to have senses that are better enhanced than those of humans. They are also believed to be able to adapt to a variety of different situations in their environment.
ReplyDeleteSources:
http://www.digitaljournal.com/article/190214
http://www.sharks-world.com/humans_and_sharks.html
Danielle Webb (dwebb456@gmail.com)