Analogy/Homology
A. Briefly describe two different species that possess the homologous
trait.
-Two species that possess the homologous trait would be an alligator
and a human. An alligator is a reptile that can live both on land and in water.
The alligator has four legs and tail. The human is the sophisticated species
that stands on two legs and has the capability of reason. Both these species
share a similar skeletal structure particularly in there forelimbs. Just as a
human species, the alligator forelimbs contain the humerus, radius, ulna, and
carpals.
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 two species?
-The homologous forelimb of the human species is formed from
the humerus bone which forms the upper arm, and the ulna and radius which are
two bones forming the lower arm connecting to between the elbow and wrist joints.
This allows rotation and bending in the arms which alligators are not able to
do. These bones are generally large compared to the alligator since the
alligators usually do not need to reach out the arms with their longer snouts
and stronger tails helping them easily catch prey and move around on land and
water. The relationship between limbs and body differ as alligator forelimbs
tend to be short, come in fours, and close to their bodies with an outward
pose. The human forelimbs are typically aligned parallel with the body while
also typically being longer and bigger.
C. Who was generally
the common ancestor of these two species and how do you know that the ancestor
possessed this homologous trait?
-Since the alligator
and the human both contain vertebrates, forelimbs, and a similar skeletal
structure a common ancestor can plausibly be either the dinosaur itself or any
reptile millions of years ago who had the back bone vertebrate as well as the
forelimbs and skeletal structure resembling that of a mammal or humans.
A. Briefly describe the two different species
that possess the analogous trait.
-Two species that possess the analogous trait would be a
dolphin and a shark. The dolphin and shark are two seawater dwelling species
whose similar outward appearances and body shape allows for quick and deadly
speed underwater. The analogous trait found in both the dolphin and the shark
would be their fins, body shape, and flippers.
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 flippers, fins, and body shape of the two species are
used primarily for survival. The fins of the two species are used to help guide
the animals through the water making sharp cuts and faster bursts of speed. Similar
to the fins, the flippers and body shape are also used for the movement and
speed of the animal through the water. However, the dolphin does slightly
differ by having a more narrow and rounded front face, fins, and body. What
really differs between the two species is the structure found within the
flippers of the two animals. For instance, the dolphin contains a skeletal
structure of a mammal that contains the ulna, radius, and humerus. This cannot
be found in the shark.
C. All pairs of
organisms share some common ancestor if you go back far enough in time. Did the
common ancestor of these two species possess this analogous trait? Why or why
not?
- The two species are
analogous since there is no common ancestor, instead we see the similar traits
evolved within the species overtime independently from each other. We can see
this simply through the bone structure of the fins from the two species. Since
the dolphin’s structure in its fin contains the ulna, radius and humerus, it is
certain that the dolphin is a mammal and has evolved to become a sea mammal.
Unlike the shark whose bone structure suggests that their ancestors had evolved
from the sea, and only evolved to adapt to the surrounding environmental
changes.
Great opening description of your species pairing, for both your homology and your analogy section. Thank you.
ReplyDeleteYou explain the reasons why the human arms is structured the way it is, but when it comes to the alligator, you only explain why it *isn't* shaped like a human arm. It isn't designed to do this or that. So what IS it evolved to do? How does it benefit the alligator? What is its function? Alligators and crocodiles have retained their general structure for millions of years. Their structure must work for them and it would have been good to explore why it is so adaptive.
RE: Ancestry... Dinosaurs essentially went extinct (except for birds) and didn't give rise to living reptiles or mammals, but the common ancestor was an archaic reptile of some sort. This isn't because of anatomy but because of the evolutionary history of the vertebrate family tree... archaic reptiles gave rise to modern reptiles, mammals and birds. But you are correct that this archaic reptile possessed the early limb structure (evidenced by the fossil record) that was then passed on to the two species in question here. That's what we need to know to confirm that these are homologies.
Good discussion of your analogous traits, but keep in mind that what is interesting here are the similarities, not the differences. We aren't surprised to see differences in non-genetically related species. We can be more surprised by the similarities and those need to be explained in terms of similar selection pressures producing the similar structures and functions.
"The two species are analogous since there is no common ancestor..."
Nope. There will always be a common ancestor. The question is, did the trait arise from that common ancestor? The answer is "no" if these are analogous traits.
Otherwise, good attempt at explaining the ancestral evidence supporting the claim of analogy. Here's another way to say it:
The common ancestor of the dolphin and shark is an archaic fish, who did possess these fin structures and also passed that trait onto extant shark species. So the question is, did the dolphin also inherit it's fin from that common ancestor? As you correctly explain, dolphin "fins" evolved after dolphins split off from terrestrial mammals, i.e., long after the split with ancient fish. This provides us with the evidence we need to confirm that this trait did evolve independently in at least one of these organisms, making these traits analogous.
Good images.
Great post. I would have never thought us humans have the same skeletal structure as an alligator. I know that we both have 4 limbs but I would have never thought we could compare to them. That is very interesting to learn and read about. Great Post !
ReplyDeleteHey there Isaac - Yet another entertaining post! Thanks for that man. I enjoyed reading and did not realize that alligators and humans actually have the same type of bones in their arms... Incredible! The only thing I did not follow was the common ancestor, which I saw Dr. Rodriguez did clarify. Although I'm sure there were similarities between dinosaurs and alligators and humans, I didn't quite think that that would the common ancestor. But again, great post and I learned a lot!
ReplyDelete