Homologous Trait: limbs
Two species that share a homologus trait are a human and a dog. Humans are of the primate genus Homo, specifically a member of the species homo sapiens. Dogs are mammals that are of the genus Canis and are a subspecies of wolves. The dog was the first species to be domesticated and they come in many different breeds. They have long been associated with humans, which has led them to be uniquely attuned to human behavior.
The arm of a human and the leg of a dog are considered homologous structures because they have a similar underlying anatomy. Our arms have the same bones and joints as the front legs of dogs. As the photo depicts, we share radius', ulnas, carpals, metacarpals, and digits. Humans use their arms for a range of things, but to name a few they are used for lifting, carrying, or throwing things. Dogs use their front legs for walking, running, and digging. Researchers speculate that the common ancestor of the human and dog is the insectivore.
Analogous Trait: Flippers
Two species that share an analogous trait are penguins and dolphins. Penguins are from the Spheniscidae familyand evolved from flying birds. They reside in the Southern Hemisphere. They are usually in an upright position and walk on short legs. Dolphins are from the cetacean family and evolved from land-dwelling mammals of the artiodactyl order. They generally prefer warmer climates. Although they live in the ocean, dolphins are still classified as mammals. They have a dorsal fin that runs the length of the body.
Penguins and dolphins both use their flippers for progression through water. Specifically, they both use their flippers to change direction and to manage their movement while in the water. The penguin’s flippers are supposed to be the vestiges of wings because they evolved from flying birds, however now they use their flippers to swim through water and cannot fly. Given that dolphins are mammals and penguins are birds, this is an example of convergent evolution where analogous structures with a similar function develop from unrelated bodily structures. These species do not share a recent common ancestor, but these similar appendages (flippers) evolved to help them survive in an aquatic environment.
Homology: Good opening description of your two species.
ReplyDeleteGood connections drawn between the structure and function of your two traits and their relative environments. Recognize that we can even simplify this by understanding that the human forelimb is predominantly manipulative in function/structure while the dog forelimb is locomotive.
"Researchers speculate that the common ancestor of the human and dog is the insectivore."
A couple of issues:
"Insectivore" just means they eat insects. This only indicates diet, not ancestry. But beyond this, this section asked you to confirm that the common ancestor possessed the archaic version of this trait and passed it onto these two species. This is how we confirm that these traits are indeed homologous. How can we do this?
Both humans and dogs 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 limb structure and passed that onto these two descendant species, with changes concurring over time due to differences in the environment function (manipulative vs. locomotive). That is what we need to know to confirm common genetic origin and confirm homology.
Analogy: Again, very good opening description.
"The penguin’s flippers are supposed to be the vestiges of wings"
They ARE derived bird wings. Nothing "supposed" about it.
Otherwise, good discussion in this second section. You describe the similarities in these traits in terms of their structure, function and commonalities in environment.
"These species do not share a recent common ancestor, but these similar appendages (flippers) evolved to help them survive in an aquatic environment."
As explained in the guidelines, ALL organisms share a common ancestor if you go back far enough. The question is, did that common ancestor possess the trait in question and pass it on to both of these modern species? If so, these traits are NOT analogous. This section is a "check" to confirm their analogous status. So how do we do that?
Dolphins are mammals, who arose from archaic reptiles. Penguins are birds, who also arose from an archaic reptiles, so the common ancestor was an archaic reptile. We know from the fossil record that the generalized limb structure of reptiles did NOT include fins, but we also know that the fin structure in both of these species arose long after this split with the common ancestor. Dolphin fins arose after they split from terrestrial mammals and penguin fins are derived bird wings. That is what we need to know to confirm that both these traits arose independently from that common ancestor.
Good images.
Hello Smith,
ReplyDeleteI really appreciated the background detail that you gave before delving deeper into your examples of the leg of the dog and the arm of the human, as well as the flippers of penguins and dolphins. Additionally, the amount of depth you included in your post felt very detailed yet concise, which worked very well to convey to the reader the answers to the various questions in the prompt. I also included a picture that diagramed the skeletal layout of my animals though I think you did a better job by having both examples in one distinct image.
It was interesting that you had the dog and human comparison I would have never thought of the two being similar. Also I like how you went in detail about the certain bones and cartilage that we have in common with canines. Especially finding out they have metacarpals as well as humans.
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