There are many species all over the globe some different and some similar. What makes these species similar isn't always a common trait but a common ancestor. For example the species Canis also known as the Dog shares a common trait with the Delphinus or the Dolphin. The trait they share is the composition of the fore limb. They both have a humerus, ulna, radius, and carpals but they are not the same size nor are they used in the same way. In the dolphin these bones are much thicker and shorter allowing the dolphin more power and speed through the water but resulting in making this a specialized trait. For the dog these bones are much longer and thinner allowing the dog to dig and hold things down making a generalized trait.
Now heres an example in which two species share the same. Trait but do not have a common ancestor. Take the Homo Sapien also known as Humans and the Hapalochlaena Lunulata better known as the Blue Ringed Octopus or BRO for short.The trait that we share with the BRO is our eye structure, more specifically our vision. Our eye has been transformed to have stereoscopic vision meaning to see in three dimensions. The BRO also has this visual advantage. It uses it just in the same way we do to look past or around objects. Although there is no common ancestor for us and our bro the BRO it is estimated that this particular trait showed up around 500 MYA.
A suggestion: For each section (homology and analogy) there are three prompts that you need to address. It would be better to separate your response to each prompt into separate paragraphs so I can clearly understand which information is meant to answer which questions. You have plenty of room here. No need to cram everything into one paragraph.
ReplyDeleteThe opening prompt for both sections specifically ask for descriptions, not just identifications, of your two species. Expand and provide your readers with a better foundation of understanding for these comparisons.
Homology: Very good job explaining the differences in structure via the differences function. Well done.
Missing the ancestry section here? How do we know that these traits are genetically related and therefore homologous?
Good images.
Analogy: The eye is a classic analogy example, with that trait having evolved separately several times in Earth's evolutionary history. Does the octopus eye have a blind spot like human eyes do?
Ancestry: Stating that there is no common ancestor is not sufficient here. What evidence do you have for that? As stated in the guidelines, if you go back far enough, all organisms share a common ancestor. The question is, did that common ancestor share this trait?
In many analogous comparisons, it is easier to figure out this information. I don't know much about octopi or sea stars, so I had to dig to figure this out. While I don't allow Wiki sources, they have their advantages. I googled both organisms independently in two different windows and up pops for each a little Wiki window. In that window is a brief description, along with an indicator of "higher classification". I clicked on that to find the higher order, and then I kept clicking on that until I found the point where both species had the same classification. Essentially, I walked backwards on their family tree. Then see if the trait in question is general trait of that group. It isn't in this case, so you can confirm that the trait is analogous, and this is confirmed from genetic evidence. Try that out and see what I mean.
Chris I like the analgous trait comparison that you used, in particular the image that you used that clearly illustrates the similarities between a human eye and the eye of an octupus, all the while noting that we do have the same stereoscopic vision of an octupus. For the homologous traits, you included the official name of the dog, Canis, which most people probably did not know.
ReplyDelete-Nate