Homologous traits are those that are shared between two different species. This means that they have shared a common ancestor that passed on said trait onto the individual species. The structure may be somewhat different, but they still bear the same underlying anatomy.
Analogous traits are those that, although similar, are not due to species bearing a common ancestor, but rather due to similar environmental pressures bearing down on both species to develop that trait to a similar state.
Question 1:
A: The homologous trait discussed would the forearms of gorillas and those of humans.
B: Both species bear a hand and forearm consisting of a humerus, ulna, and radius, with multiple carpals and metacarpals conjoining the hand to the forearm. These bones are found to have relatively the same structural assignments to each part of the forearm. The bones of a gorilla are somewhat larger than those of humans, however. This may be due to a change in the environment that affected survival (gorillas may need more arm length to climb, gather food, etc... whereas humans have no need to do such).
C: Humans and gorillas share roughly 96% of their genes. It is believed that gorillas and humans bore a common ancestor roughly 10 million years ago, during the slow rise of the great apes variation. The assumption was taken after a study focusing on gorillas in the western lowlands.
D: An image comparing the hand structure and forearm development:
http://media-1.web.britannica.com/eb-media/95/55495-004-84E08ECB.jpg
Question 2:
A: The analogous traits discussed would be the dorsal fin of a shark as compared to that of a dolphin.
B: Shark fins are heavily rigid, and composed of cartilage. The dorsal fin is meant to lift the shark, keep it stable as it swims, and aid in propelling the shark forward. The dorsal fin of a dolphin, however, are made of a connective tissue and helps with keeping the dolphin in it's upright position. A side note, the dorsal fin is also capable of releasing excess heat. The major point is that they aid in maintaining balance for the creature and help in mobility.
C: This trait is indeed analogous, evolving independently. The original ancestor had no need for the dorsal fin, as the environment had not required some adaption to such, or perhaps that the dorsal fin was the evolutionary reaction gained form an additional fin to aid in support. Again, the common ancestor must have not had a need for such at the time.
D: An image comparing the outer anatomical structures of the sharks vs. the dolphins
http://evolution.berkeley.edu/evolibrary/images_pamphlets/sharkdolphin2.jpg
There is a little more to homologous traits. It isn't just that they are shared through common ancestry. They also exhibit structural and functional differences due to different environmental pressures. Without those differences, they are just shared traits.
ReplyDeletePart A asks for a brief description, not just identification. Expand.
On the right track in Part B for your homologous pairing because you do identify differences in structure. You say that gorillas require heavier bone structure do to the environment, such as climbing and gathering food, but why don't all non-human primates have that heavy bone structure? They also climb and gather food. What is it about the environment of the gorilla that produced such heavy bone structure? Also, you say that humans don't need this heavy bone structure but you are only explaining why humans *aren't* a particular way. Can you explain why humans have the bone structure that they have? What do humans use their bone structure for in their arms? Climbing and gathering food? Or for something else?
Correct humans and gorillas share a significant portion of their genome, but given that they do have differences, how do we know that the arm structure is part of that common ancestry? Can we also confirm this by comparative anatomy of all mammals? Gorillas and humans are both mammals and all mammals share similarities in their forelimbs since they inherited that structure from a common mammalian ancestor.
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Good description on your analogous traits (though again, Part A required more than just identification of your species).
For ancestry, actually the common ancestor of the shark (a cartilagenous fish) and the dolphin (a mammal) was an early cartilagenous fish. That means it DID have the dorsal fin, correct? In all likelihood, it passed that fin onto it's fishy descendents, including the shark. So does that make this a homolog? It depends upon the dolphin. We know that dolphins are mammals who started off as land animals before adapting to the aquatic environment. That was when the fins evolved and it means the fins in dolphins did arise interdependently from that common fish ancestor with the shark. But you need to go through that logic process to confirm analogous status.
I always find it very interesting when ever the "human" is compared to monkeys, gorillas , apes, homo sapiens, because i get to learn a little more . i was not able to see the pic.... but i'm sure it was a good picture showing the difference between their bone structure.
ReplyDeleteNice post. had issues trying to view the pics.