a. Two different species that possess homologous traits are dolphins and humans. Dolphins and humans happen to both be mammals but one lives in the ocean and the other on dry land. Dolphins seemingly have the structure of a fish but are actually more closely related to human anatomy surprisingly.
b. When looking from the outside, a dolphins fin and a humans arm look completely different, but when looking internally you find undeniable similarities. Each structure possesses the same bone formation; phalanges, carpals, ulna, radius and humerus. These structures in the dolphin help it move swiftly through the water and to communicate with other dolphins. A humans arm, as we all know, use are arms to lift, grab, climb, hold, etc.
c. Some say that, humans at one point in evolution went through a semi-aquatic state but then evolved to survive on land. In my opinion its possible that apes evolved from dolphin-like creatures and then we evolved from apes .
2. Species with Analogous Traits
a. Two species with analogous traits are the dolphin and the shark. I like to use the dolphin again because of its similarities to both fish and mammal.
b. Dolphin and sharks obviously have very similar body structures; a dorsal fin, two pectoral fins, and a dorsal fin. On both animals the fins act in the same ways to move the animal and keep it agile and swift in the water.
c. Even with such obvious similarities, these two ocean dwellers cannot have a common ancestor because one is a mammal (breathes air) and one is a fish (has gills).
Good description on the homologous traits.
ReplyDeleteWith regard to ancestry, I'm increasing concerned with the number of students citing the "Aquatic Ape Theory". There is no good supporting evidence that this is a valid path of evolutionary history for humans:
http://skeptoid.com/episode.php?id=4357#bottom
But you don't even need to speculate on this for this discussion since we have a very good idea of how aquatic mammals evolved, and they did arise from land mammals. The ancestral limb structure of both humans and dolphins is that skeletal structure of bones you describe in your post. They do share a common ancestry but the differences in structure are directly related to their differences in environment (non-aquatic vs. aquatic) and function (non-locomotion vs. swimming).
Great description of your analogous trait. You make a jump in logic with regard to ancestry that isn't valid. Mammals and fish do share a common ancestor, namely early fish, if you go back far enough. The question is, did both organisms inherit their fin structure from that early ancestor? Sharks did, but because we understand that dolphins developed their fins as derived mammalian limbs, we know that they did NOT inherit their fins from that early fish ancestor. That is what makes these traits analogous.
Good images.
Overall I enjoyed reading your post. I do not think my comments will be able to compare to the one before mine though. L. Rodriguez really seems to know a lot about this subject.
ReplyDeleteI did however choose to do my assignment as well on dolphins and humans. It seems we may have read the same articles on it. I do not know as much as Rodriguez does but I did come across quite a few theories about humans evolving from a aquatic ancestor so I made a comment on that too. But even if it is a false theory with no good research done on it at least I can learn from that and hopefully get to a clearer answer. Thank you for that link Rodriguez.
Kari, you did a great job explaining analogous traits as well. Very good job
-Karen Brown