Homologous Trait
a.
Briefly
describe (not just identify) the two different species that possess the homologous
trait.
Listed
above you have a human hand and a limb of a cat. These are homologous
structures because although they appear to be completely different and have
different purpose, they are similar and share common traits. One of the
similarities is the forelimb bones (tetrapods). They have the same basic
pattern of bones as shown above, due to inheriting the pattern from a common
ancestor.
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. (10 pts)
Human arms
and cats front legs are homologous traits shared between the two. The human
species uses its arms to manipulate the environment around them and we also use
our arms to communicate, assistance in feeding and to navigate. Cats use their
front legs for navigating and for hunting. Cats however do not control their
environment like we do and their focus is simply to survive. Humans and cats
share a common large upper bone in their respective arms and lower section of
the appendage. It is made up of two bones in both species. Humans and cats are
classified as mammals and share a common ancestor that had the same bone
structure. All mammals today have the same structure as well. The backbones in
mammal serve as an example of ancestral homology because this trait originated
before mammals common ancestor. Other shared traits are morphological
homologies (shared anatomical), ontogenetic homologies (developmental or
embryonic similarities), and molecular homologies (similarities in genetic
code). ("Introduction toAnthropology", 2015)
c.
Who
was (generally, not specifically) the common ancestor of these two species and
how do you know that ancestor possessed this homologous trait? (5 pts)
The common
ancestor of these two species is called Dormaalocyon latouri. It
is a cross between a panther and a squirrel. It lived about 55 million years
ago. It possesses the same four limb bones as found in humans and cats. See image
below. This is how I know that the common ancestor possessed this homologous
trait.
Analogous trait
a.
Briefly
describe the two different species that possess the analogous trait. (5 pts)
Sharks
and penguins share analogous traits. The penguin is consider a bird and has a
wing. The shark is a fish and has a fin. They live in two different
environments. The shark lives in the ocean where its cold salt water and
penguins live in the ant Arctic Ocean where it is icy cold. The differences in
environments for these two animals makes their wings and flippers analogous
traits. (“These examples of Analogous structures will surely surprise
you,” 2016).
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. (10 pts)
The
penguin through time has evolved and adapted to their environment. A penguin’s
wing has evolved into a flipper where the bones are denser and closer together
which forms a paddle. They use this to help them propel through water. They are
also flightless creatures due to their bone structure. Sharks also use their
fins to help move through water and help me propel straight up to catch their
prey. They both have body parts that appear similar but belong to a different
class of vertebrates. “In many cases analogous structures, or analogues, tend
to become similar in appearance by a process termed convergence.”("Analogy,"
2016).
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? (5 pts)
Analogous
structures is one that doesn’t indicate there is a recent common ancestor
between two organisms. The anatomical structures may be similar and perform the
same functions, they are actually a product of convergent evolution.
Good choice of homologous traits and well done, in general, on your description of the species. You also do well explaining the differences in function and the environment that led to divergent evolution producing differences in structure.
ReplyDeleteOne caution:
" and their focus is simply to survive"
A little broad and judgmental. I could easily argue that, at our very biological roots, that is what drives us as well. But from within the species, we tend to adopt a rather biased view of our lives compared with other animals. Let's pitch the bias while in the class and just stick with biological facts.
I'm having trouble picturing a cross between a panther and a squirrel! :-) But regardless, we don't need to get this specific to determine whether these traits are indeed homologous.
Both humans and cats are mammals, and therefore share a common mammalian ancestor, but definition. We know from the fossil evidence (such as the images you present) that these archaic mammals possess the primitive mammalian limb structure, passing it onto these two descending lines, with differences arising as a result of divergent evolution. This is what we need to know to confirm homology.
Good choice of analogous traits and well done on your description of the species along with the explanation for their similarities in structure regardless of the lack of shared ancestry in those traits.
With regard to ancestry, some clarification:
"Analogous structures is one that doesn’t indicate there is a recent common ancestor between two organisms. "
No. To be specific, analogous traits are similar in function and structure, not because of common descent from a shared ancestor but because of parallel evolution producing similar traits. It doesn't have anything to say about the recent-ness of the ancestor. Just that the traits were not inherited from that ancestor in at least one of these organisms.
So with regard to penguins and sharks, what do we know about their ancestry that can help us confirm that these traits are indeed analogous?
The common ancestor of the penguin and shark is an archaic fish, who did possess these fin structure and also passed that trait onto extant shark species. So the question is, did the penguin also inherit it's fin from that common ancestor? Penguins are birds, but let's take that information further to address this issue. Penguin "fins" are actually derived bird wings. Birds evolved wings when they split off of their reptilian ancestor, 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.
Your post is really well written. I really like your choice in examples. I never thought about why the penguin doesn't fly, but knowing that it is because of denser bones is interesting, as typically bird bones are hollow.
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