Wendy N Flores
Anthro 101
Summer 2016
Blog Post: Analogy
& Homology
1. For your homologus traits provide the following
information (25 pts):
a. Briefly
describe (NOT just identify) the two different species that possess the
homologus trait. (5 pts)
My two species are a
frog and a bird. A frog is an amphibian who is able to leap long distances, has
a long tongue, and varies in different colors and shapes. A bird is a mammal
who has the ability to fly a high distance in the air, has great eye sight to
be able to hunt for food on the ground, fast in agility, and they also vary in different
colors and shapes.
b. Describe the
homologus trait of each species, focusing on the differences in structure and
function of the trait. Why do these
homologus traits exhibit differences between the two species? Make sure your explanation is clear and
complete. (10 pts)
The homologus trait
that my two species share are a common set of bones: the radius, ulna, and
humerus bone. The difference in the structure of the frog is that its legs are
long and (the skin that is attached to the body and leg extends and looks like
a birds wing) they extend a far distance so that the frog may be able to leap
across long distances so that it may be able to feed, and escape predators. The
difference in the structure of the bird is that its wings give them the ability
to fly, they too have the same structure like the frog but they developed it as
wings. They developed wings so that they may be able to look for food and be able
to escape predators in the ground. The forelimbs of these two species look very
different because they have evolved differently to account for the specific
lifestyles of each animal.
c. Who was
(generally, not specifically) the common ancestor of these two species and how
do you know that ancestor possessed this homologus trait? (5 pts)
“The shared bones date
back to a pre-historic fish that emerged onto land, eventually becoming an
extinct transitional animal from which they evolved.” The reason why I believe
that the ancestor possessed the homologus trait is because the fish came onto
land and for it to come onto land it had to have limbs.
d. Provide an
image of each species in this comparison.
(5 pts)
2. For your analogous traits provide the following
information (25 pts):
a. Briefly
describe the two different species that possess the analogous trait. (5 pts)
My two species are a platypus and a duck. Both the platypus and duck
look somewhat similar. The platypus and the duck both carry and analogus trait
which is that they both lay eggs even though ones a bird and the other is a mammal.
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)
They’re both egg laying creatures with webbed feet and a
rubbery snout. They look very similar because they both swim in the water, lay
eggs, their nostrils are located on top of their beaks and their eyes above it,
and they both extremely have the same features, but are different species.
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? (5 pts)
Yes, I do believe the common ancestor of the platypus and
the duck possess the analogus trait. Because even though the platypus were very
poorly understood and account of the low numbers of extant species, “scientists
insist that the duck billed platypus is an evolutionary link between mammals
and birds.”
d. Provide an
image of each species in this comparison.
(5 pts)
Okay for your opening description of your homologous pair, with the correction that birds are not mammals, but belong to their own class of "aves", i.e., birds.
ReplyDeleteWith regard to the homologous trait itself, make sure you are comparing the same structures. The bones you list (humerus, ulna and radius) are the bones of the forelimb. While this accurately identifies the bones of the bird wing, they aren't the bones of the hindlimb of the frog (which is the one that provides the power leap you describe). Those bones are homologous to the bones of the bird legs (not wings), i.e., the femur, tibia and fibula. So for an accurate comparison, you needed to compare the bird wing with the frog front leg or the bird legs with the hind legs of the frog. (The image your provide compares the forelimbs with the wings.)
A couple of point on your ancestry section:
First, I'm curious as to your source of information, as in evolutionary biology, the word "transitional animal" is almost never used. All organisms are transitional between an earlier and a later form, including humans, so the word really makes no sense.
Second, do we need to go all the way back to fish to understand if these traits are homologous? The common ancestor of frogs and birds is an archaic amphibian, which gave rise to both extant amphibians (like frogs) and also reptiles which gave rise to birds. Moreover, we know that early amphibians possessed this ancestral limb structure and passed it onto its descendents, confirming that similarities are due to common descent, while the differences are due to divergent evolution. This defines homologous traits. If we go back to fish, we don't have this information, as they don't possess the limb structure we are highlighting. You have to start with that archaic amphibian.
Good choice of analogous pairs, but it would have been better to focus on just one trait instead of several, so you could address the process of convergent evolution that produced them. For example, what evolutionary environmental pressures resulted in the development of egg-laying? Or the beak structure? What common adaptive pressures produced either of these two analogous traits?
"Yes, I do believe the common ancestor of the platypus and the duck possess the analogus trait."
But then that would make this trait either homologous or just a common shared genetic trait, not analogous. Remember that analogous traits do NOT arise from common ancestry, meaning that the common ancestor did not possess the ancestral form of that trait. In this case, the common ancestor of the platypus (a mammal) and the bird (a bird) was an archaic reptile. This makes the question more interesting because some reptiles do lay eggs and it is likely they passed on this trait to birds. What about the platypus? Well, we know that egg-laying is not the normal, primitive state for mammals, so this is a uniquely derived trait of the platypus that evolved after they split from their mammalian ancestor. That independent evolution is evidence that these traits are indeed analogs. What about the bills? Can we outline a similar ancestry for that trait? Where do bills originate in these two species? From the ancestor or did they arise independently?
Good images.
Wendy I find the platypus to be a very strange animal good choice of analogous pair.
ReplyDelete