Homology and Analogy
1.
The tailbone of a human and the tail of a monkey are two examples of homology. The tailbone is actually called the tailbone because of this shared lineage. Humans don’t actually have a tail but the tailbone is the last remains of where a tail would be and it's referred to as a “vestigial.” In utero between the stages of 14-22 weeks the embyro will have a tail. As opposed to monkeys who have fully functioning tails since day one. some tails on primates are used simply for swatting flies but some also have the ability to grasp and use them to swing from trees. And the change in characteristics could of occurred as early as the first bipedal hominin.
2. A shark fin and a dolphin fin are two analogous structures. The dorsal fins of a shark tend to be more rigid and supported by cartilage; as the fins of dolphins have no internal support. Dolphins evolved from the artiodactyl, which is a land mammal with no fins. These structures evolved independently of sharks, making it an analogous structure. But only the Dorsal fin of both the shark and the dolphin are the only analogous structures since the pectoral fin is homologous.
I had a bit of trouble with this assignment but looking at you blog post if gave me somewhat of a better understanding. Thank you I think you did a good job
ReplyDeleteI find it really interesting to see the remnants of a tail in humans. It makes curious to why that particular change happened.
ReplyDeleteHello, you're so right. We still have that little tailbone but don't always know why we have it. :)
ReplyDeleteThis was the clearest explanation of the tail/tailbone homolog that I've seen yet.
ReplyDeleteOne clarification: Humans are apes, and apes in general do not have tails, so this lose of the tail happened long before humans went bipedal. It is an interesting question as to why apes lost their tails... Another research project!
Given the close genetic relationship within the primate grouping, you may have just assumed the issue of common descent, but it should have been explicitly stated for the benefit of your readers.
You were on the right track with the dolphin and the shark, including the argument that dolphin fins arose independently, until the last line:
"... the pectoral fin is homologous."
How? The fin of the shark was inherited from it's ancient fish ancestor. The fin of the dolphin is a derived trait adapted from the skeletal limb structure common in amphibians, reptiles, mammals and birds... but not in fish. They are similar in structure, but like the dorsal fin, they are independently derived.
Otherwise, good post.
(late submission)
Great examples you chose to represent your homologous and analogies. and for the sharks and dolphins having similarities is due to convergent evolution. Good Job overall
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