Wednesday, April 30, 2014

Week 3 Analogy/Homology Blog Post





Week 3: Analogy/Homology Blog Post

1. 
A) I chose the horse and the zebra for Homology.
A horse is a plant-eating mammal with a flowing mane and tail.
A zebra is an African wild horse with black and white stripes.
B) Both animals have manes and tails. A horse’s mane, if left to grow is long and flowing where as a zebra’s mane is short, mowhawk like, coarse hair that is striped. Horses are mainly domesticated and zebras are not. The most common difference is the zebra’s stripes. Different horse breeds have different coat colors and patterns but none possess the stripes of a zebra. Unless a unique breeding occurs and then a hybrid is born.
C) Animals in the genus Equus have evolved over millions of years from a deer like animal, the proto-horse, with four toes, to the species we know today that are single toed hooved animals. 
            



2.                 
A) I chose the dolphin and shark for analogy.
Sharks are long bodied marine fish that are predatory.
Dolphins are small marine toothed whales that have beaklike snouts and are social.
 B) Both sharks and dolphins have streamlined bodies, side fins and a triangular dorsal fin. The dorsal fin is necessary for larger sea animals for stability. Both species live in the ocean and prefer warmer waters. Both are predators, hunt fish and swallow their food whole. Both sharks and dolphins are fast proficient swimmers and sharks have been known to breach the water like dolphins do. The reason these two species have analogous traits is due to convergent evolution. They have had to adapt to their water environments.
 C)From what I have read, the common ancestor between sharks and dolphins is a mystery. They didn’t inherit their similar body shapes etc. from a common ancestor.
 


 

     

4 comments:

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  2. Dear Diane,
    Liked very much your analogy of the dolphin and shark. It didn’t occur to me before that the two species are occupying a very similar niche. Their body styles do appear very similar. I know swimmers and surfers have noticed this resemblance. I think it’s fascinating that one of them managed to exploit this very similar niche while being an air breathing mammal. Air breathing, endothermic, viviparous there seems to be a lot of obstacle to overcome to compete in an aquatic environment. Thanks, great comparison.

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  3. I agree that the coat color is a distinct homologous trait between these two. It is complicated by the fact that horses are domesticated animals, subject to artificial selection more than natural selection, but this can work for this trait. However, you describe the differences but you don't explain them. Why do zebras have stripes and horses do not? How are these differences the result of different selection pressures in spite of their common ancestry?

    In addition to identifying ancestry, you needed to talk about whether the ancestor possessed the ancestral trait or if these traits arose independently. With regard to the general coat of horse and zebra, the short hair structure is the same and likely arose from a common ancestor, it is just the color/pattern that is different. Again, the fact that horses are subject to artificial selection makes this comparison less than clear.

    Good discussion on your analogous traits.

    Correct, sharks and dolphins didn't inherit their body shapes from a common ancestor, but how do we know? The common ancestor was an ancient fish, and since sharks are fish (and rather ancient themselves) they inherited their body structure from that ancestor. However, dolphins are mammals and arose from land mammals, developing their aquatic body shape independently. That means the body shape is a derived trait for dolphins, making these traits analogous.

    Good images.

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  4. Hello, Diane,
    I really enjoyed reading your blog post and I found the shark and dolphin comparison very interesting! Although the two species appear similar in body style, I never realized how similar they really are. I also find it interesting that they didn’t inherit their body shapes from a common ancestor considering a shark is a fish and a dolphin is a mammal. Great post!

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