In a cat the forearm helps the cat move and walk. In a human, the forearm allows the elbow to extend or fold. This homologous traits exist due to the environmental changes for the two mammals. The common ancestor looks like a cross between a panther and a squirell Its named, Dormaalocyon latouri.
Sharks and penguins share analogous traits. Both are different considering, one is a bird and the other is a fish which results into two different environments. As shown below, a whale has a flipper located on the lateral side. A flipper helps to whale move in the ocean. A penguin possesses a wing, that also helps to bird move, except they fly instead of swim like a whale. The difference in environments for these two animals makes their wings and flippers analogous traits.
http://phenomena.nationalgeographic.com/2013/02/07/meet-the-ancestor-of-every-human-bat-cat-whale-and-mouse/
I like your comparison between the shark and penguin- linking their arm structure and ability to use it in water. Both sets of species, by the way depicted in your shark v. penguin comparison shows a great difference within each species ability to use their wing as a fin like the shark. With sharks only being able to stay underwater they developed a unique eye sight, and strengthen their ability to detect even small amounts of electric current or vibrations in water. Depending on the size of the penguin, he or she can hold up their breath any where from 1 to 18 minutes- the larger they are they longer they can hold their breath for much deeper depths.
ReplyDeleteI found your points on sharks eyes to be interesting, so I read more one it... Sharks are able to change their field of vision from being stereoscopic to monocular at will. Stereoscopic vision refers to the ability to see in three dimensions (as humans are able to do). Monocular vision is when the sharks use only one of its eyes. Also, when they are in a fight with an attacker, they will roll their eyes into the back of their head to protect them.
Deletehttp://www.sharksinfo.com/sight.html#.VMCGFntSHvQ
Delete"The forearm of a human, and the forearm of the cat (right above the paw) are identical to each other."
ReplyDeleteIf they are indeed identical, then they would have the same function and they would also not be homologous, just shared traits. While I agree that they share similar bones, did you mean to really argue that their limbs were similar in structure? I see later that you qualify this but describing the structural differences would have clarified this for your readers.
The specific ancestor is less important than understanding that, since both species are mammals, then their common ancestor was an archaic mammal who possessed this early limb structure. That is what you need to know to confirm the genetic relationship necessary for this to be a valid homologous pairing.
"A penguin possesses a wing, that also helps to bird move, except they fly instead of swim like a whale. The difference in environments for these two animals makes their wings and flippers analogous traits."
Penguins are birds but don't fly. Instead they use their wings as fins, analogous to the whale fins. This commonality in function and structure are due to *simiilarities* in environments (in this case, aquatic), NOT due to their differences. The similarities are due to parallel evolution, not due to common descent. Make sure this difference between homologous and analogous traits is clear.
No discussion on ancestry for your analogous trait? Did the common ancestor possess the trait and pass it onto both descending species? Or did the trait arise independently in at least one of them? Why is this important for determining analogous status?
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