1.
a.
Two different species that share a homologous trait
are chickens (birds) and humans (mammals); more specifically their wings and
arms, respectively. The skeletal structure of a wing from a chicken is built to
rapidly flap causing the animal to briefly elevate off the ground for several
seconds. Chickens cannot fully fly for long periods of time like other birds,
but they can jump and fly for several seconds to cover some ground. Humans on
the other hand cannot fly at all, nor can they flap their arms fast enough to
elevate. A human’s arm is utilized to grab, build, maneuver and do complex
things.
b.
The homologous trait between chickens and humans
share differences of structure between wings and arms. Wings on a chicken are
arranged so that they begin at the front part of the animal’s body, leading in a
horizontal direction towards its rear extremity. Each of these wings have three
main joints, and three fingers. Though these fingers are not as identifiable as
they are on a human’s hand. Humans on the contrary have arms that extend from
their upper body, hanging vertically adjacent to their torsos and move in
various directions.
c.
The common ancestor of chickens and humans is a
vertebrate animal. Those considered vertebrates have a vertebral column and
over time developed forelimbs, which are considered tetrapod. The forelimbs of
chickens and humans is a clear example that the limbs (wings and arms) are
homologous; meaning that they derive from a common ancestor.
d. Skeletal image of a chicken wing and human arm.
2.
a.
Two animals from different species that share an
analogous trait are rabbits and kangaroos. Rabbits are mammals that live on dry
land, with agility to move around. Kangaroos are marsupials that also live on
land. Both these animals have similarities in appearance; fur, ears, four legs,
and strength in hind legs.
b.
These two animals’ main analogous trait are
their hind legs. The strength on their legs could help them bounce from
different locations in a highly agile manner. This gives them the opportunity
to evade predators and get to locations in a short amount of time. The structure
of their hind legs is similar and much bigger in size compared to their front
legs. Clearly, they utilize these powerful legs to catapult from one place to
another in order to mobilize.
c.
We know that these are analogous traits because both
animals are from different species. Rabbits are mammals and Kangaroos are marsupials,
therefore they don’t share a genetically common ancestor. They both however are
classified and branch from Chordata into Vertebrata and Mammalia.
d.
Image of a rabbit and kangaroo.
I thoroughly enjoyed your description of our own similarities to a chicken, such a strange and compelling thought. In my own research I found that humans share a lot of traits with other animals starting with the similarities with our own arms, and it just makes the big picture that much more clear. As for your analyzation for your analogous trait, I never realized the vast majority of similarities shared between the kangaroo and rabbit. From the pictures shown, it basically looks as if the Kangaroo is a bigger version of the rabbit.
ReplyDeleteGreat job on your blog post, I look forward to reading the next one.
The opening prompt for both sections specifically ask for descriptions of the species, not just identifications of your two species or a description of the traits. Expand and provide your readers with a better foundation of understanding for these comparisons and the adaptive forces that drove these processes.
ReplyDeleteHomology: So you offer a detailed anatomical description of these two traits in the second paragraph, but you don't make a connection between how these structures are related to their function. We need both sets of information here to understand the divergent evolution that produced them. How does the shape of the forelimb in the chicken help with the function of that limb (keeping in mind that chickens are actually domesticated animals and have lost their flight function due to artificial selection... perhaps choosing a different bird would have been wise?)? And how can you explain the structure of the human forelimb in terms of it's function?
" The common ancestor of chickens and humans is a vertebrate animal."
That's too general. That could be a fish, an amphibian, a reptile, a mammal or a bird. Can you be a little more specific? "Tetrapod" has the same problem... that's just any animal with four limbs. So how do we use ancestry here to confirm that these are indeed homologous traits?
We know that humans are mammals who arose from reptiles. We also know that birds arose from reptiles as well, so the common ancestor would have been an archaic reptile. We also know from the fossil record that early reptiles possessed that generalized reptilian forelimb structure and passed that onto these two descendant species, with changes concurring over time due to differences in the environment (flight vs. manipulatory... notice that I'm stating this in terms of function within the environment). That is what we need to know to confirm common genetic origin and confirm homology.
Analogy: Better description here but could have been expanded greatly to help us understand these organisms more clearly.
The trait here needs to be very specific and here's why: If you just specific the hind limbs, then those are homologous traits. The hind limbs of these two organisms arose as a result from common genetic descent from an archaic mammalian ancestor, with differences arising due to different functions and environmental pressures. That describes homology.
Or you could identify the trait in question not as the hind limbs but as the powerful bones and musculature (structure) that allows for powerful leaps and jumps for both speed and also evasion of predators (function). In both cases, the direct ancestors of these organisms (both rodents) did NOT possess these large powerful haunches, so the trait arose independently in both organisms. Similar structure and function arising not from common genetic origin but due to similar selections pressures... that describes analogous traits.
Does the distinction here make sense?
"Rabbits are mammals and Kangaroos are marsupials, therefore they don’t share a genetically common ancestor."
As you go on to indicate, marsupials ARE mammals, so they definitely share a genetically common ancestor, namely an archaic mammal. This is why it takes a bit more detail to distinguish this as an analogous trait rather than a homologous one. For an explanation on the ancestral description that allows this to be analogous and not homologous, see above.
Good images.
No kidding when they say that we all are connected. I would of never thought we had a common trait with the chicken. I was a little curious after reading your blog and did a little research. I found that genetically we are 60% similar to the chicken. who knew? Nice pictures!
ReplyDeleteInteresting choices, I personally chose chimpanzees and humans for my homologous species and sharks and dolphins for the analogous. Also the similarities for the analogous hind legs was very clear and concise.
ReplyDelete"Chickens cannot fully fly for long periods of time like other birds, but they can jump and fly for several seconds to cover some ground."
I never understood chicken wings. Interestingly this seemingly useless feature of the chicken might have been useful for the ancestor that was shared, or at least that's the only explanation for why I think this trait exists within chickens. Regardless, clear pictures, especially the rabbit and kangaroo ones.
Hello, I found your post interesting. I would have never thought we shared an ancestry with a chicken. I enjoyed reading your response to the analogous section also. The rabbit and kangaroo are an interesting choice and although they are both mammals they might share some homologous traits too.
ReplyDelete