a. Briefly describe (not just identify) the two different species that possess the homologous trait.
-The two species that possess the homologous trait are: The giraffe and a human; while they both contain several similar structures, I am going to focus on the fact that, like other mammals, they both have seven cervical vertebrae.
b. Describe the homologous trait of each species, focusing on the differences in structure and function of the trait. Why do these homologous traits exhibit differences between the two species? Make sure your explanation is clear and complete.
-While both humans and giraffes have seven cervical vertebrae with a nuchal ligament and both species use their necks to move their heads as needed, the giraffe's bones are significantly longer, (approx 1 ft long) and are bound together with ball-and-sock joints, thus giving them more flexibility. Male giraffes also use their necks during mating season to so called "go neck to neck" for females.
c. Who was (generally, not specifically) the common ancestor of these two species and how do you know that ancestor possessed this homologous trait?
-Both giraffes and humans are placental mammals and and their common ancestor (for all placental mammals) is what is referred to as a tiny, furry-tailed creature that evolved after dinosaurs. Also described as a tree climbing, insect eating mammals.
d. Provide an image of each species in this comparison.
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For your analogous traits provide the following information:
a. Briefly describe the two different species that possess the analogous trait.
-Two species that possess the analogous trait are snakes of North America (e.g. rattle snake) and snakes in Australia (death adder). Snakes on both continents are ambush predators, stout bodied and have the ability to camouflage themselves; however they are dramatically different in diet.
b. Describe the analogous trait of each species, focusing on the similarities in structure and function of the trait. Clearly explain why these analogous traits exhibit similarities between the two species.
-The physical similarities of those snakes are thought to be due to evolutionary advantages. Snakes on both continents are slender, fast moving, burrowing snakes with similar body forms and yet they evolved independently of each other in response to convergence. Their similar body types evolved to help improve capturing prey. These snakes are dramatically different in what they eat. (e.g. most small snakes in North America eat invertebrates such as spiders, scorpions, slugs and centipedes and in Australia, those snakes tend to eat lizards and other snakes.)
c. All pairs of organisms share some common ancestor if you go back far enough in time. Could the common ancestor of these two species have possessed this analogous trait? How do we know these traits are analogous and not genetically related from common descent?
North America is home to several groups of snakes, however only the elapids colonized in Australia approximately 12 million years ago. Elapids have hollow and fixed fangs that allow injecting venom and are now found worldwide (e.g. king cobras, coral snakes, mambas and kraits). Evolution played a role over a million years ago for Australia's elapids to diversify and specialize through adaptive radiation. Over time, these Australian snakes took on most of the body forms of those found in North America.
d. Provide an image of each species in this comparison.
death adder
rattle snake
The opening section in both the homologous and analogous areas asked for a description of your species, not just identification. This would help your reader understand the environment and behavior of the species to better understand why their traits evolved the way they did. Needed to be expanded.
ReplyDeleteGood description of the unique traits of the giraffe neck... but what about the human neck? Both needed to be addressed here. Don't assume that just because we are also humans that our traits shouldn't be addressed with equal detail.
Yes, the common ancestor of these two creatures was an archaic mammal... but how does that confirm that these traits are homologous?
Both humans and giraffes are mammals, so we know that the common ancestor would be an archaic mammal. We also know from the fossil record that early mammals possessed that generalized mammalian neck structure and passed that onto these two descendant species, with changes concurring over time due to differences in the environment (aquatic vs. terrestrial). That is what we need to know to confirm common genetic origin and confirm homology.
Much better description of your analogous species.
While I recognize the differences in diet, remember what we are trying to understand here... how traits arose via convergent evolution. So what we are actually looking for are traits that are *similar* due to environmental pressure. Differences in diet don't meet that definition, correct?
It is very difficult to find analogous traits in closely related species. Broadening out your scope, it might have been good to compare the venomous trait of these snakes to the venomous trait in other organisms, such as spiders. Those are similar traits, serving similar functions, but which arise due to convergent evolution, not due to common genetic descent.
Good images.
I love that you chose the challenge to compare giraffes and humans! You described the trait of our necks being similar and I never would have thought that giraffes also have just 7 vertebrae in their necks like us, but the difference being found in how long the bones are. The comparison pictures that you entered are extremely deleted as well, which really helped depict your points. Your snake comparison for analogous traits seems really closely linked together so it was hard for me to understand but overall your posts was really quite informative and well-worded!
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