a.
Briefly describe the two different species that
possess the homologous trait. (5 pts)
For this assignment I chose the front limbs of human
beings and fruit bats as the homologous structures that I will discuss.
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 bones of a human's
front limb are homologous to the bones of a bat's front limb. Both limbs
contain the same type of bones, end in five digits, and have the same overall
structure despite the differences in size. The two limbs have changed over time
due to the uses performed by each species. Humans use their front limbs for
eating, working, handling objects, etc. The front limbs of bats are actually
covered by skin-like structure covered in hair that is used to as a part of the
wing span that the bat uses to fly. In humans the finger-like bones do not
extend very far because the uses for these structures has been used primarily
for grasping and poking whereas the finger-like structures in the bat have
elongated over time to form webbed wings which have adapted to their continued
need to fly and remain airborne. The stretch of the bones allowed the length and
width of the bat wing to extend in order to meet these needs which accounts for
the difference in the way each limb looks today.
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)
According to
Wildclassroom.com there are some scientists who have theorized that fruit-eating
bats may have evolved from the Primates making this the common ancestor between
them and humans. It’s obvious based on their scientific classifications that
they are linked. For example, both humans and bats share the following
classifications:
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Although many species fall
into these categories this is reason enough to suggest that they come from a
common ancestor. Additionally the classification system developed by Linnaeus
is based on common ancestors so the fact that both species share common classification
groups is indicative of the fact that they share an ancestor. According to www.pbs.org, naturalist Karl Ernst von Baer observed
that vertebrate animals, during the early stages of their embryological
development, seem to have a common design, whereas the adult forms show
difference. Arm buds from different species, are virtually indistinguishable
when they first form on the embryo, yet they may develop into a wing, an arm,
or a flipper.
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)
Fish and Penguins.
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)
Penguins and fish are
analogous based upon their similar “flipper” or fin-like structures. Both
structures have different uses for each but they both originate from a need to
navigate in the water. Fish use their fins to navigate through only water as
fish are not land animals. Penguins on the other hand are both land and sea
animals. According to www.livescience.com
some scientists believe that penguins were originally only “land” animals but
over a period of time evolved to spend prolonged periods of time under water in
order to forage for fish and to survive by using water to escape from other
animals that would hunt them for food such as polar bears.
Both penguins and fish use
their fins “flippers” for navigation as well as for balance. Both types of fin
exhibit similarities in structure. The humerus, radius, ulna, and phalanges are
present in the structures for both animals. Despite being arranged differently it
is clear, based on the similarities in structure, that the fins of these two
animals show the ways in which each species has adapted over time.
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)
According to
LiveScience.com there is evidence that the common ancestor of these two species
is some type of sea turtle that evolved from another type of fish called an
ichthyosaur to a leatherback sea turtle which are now extinct and over time
into the penguin. Both of these species had fins that allowed them to navigate
through the water so yes they did share this analogous trait.
e. Provide
an image of each species in this comparison.
(5 pts) A
dolphin's flipper, bird's wing, cat's leg, and the human arm are considered homologous structures
Good discussion on the homologous limb structure of humans and bats. You did some in depth research into the issue of ancestry, but the issue is actually simpler than this. Both humans and bats are mammals, and we know that all mammals tend to share this basic limb structure, which was inherited from a common mammalian ancestor (who in turn inherited it from the reptilian ancestor). As long as you know the common ancestor possessed the trait and passed it on, then these two traits with drastically different functions are homologs.
ReplyDeleteA note on the opening section for both: It asks for a description of the species, not just identification.
For the most part, good discussion on your analogous traits, but you got into some trouble on ancestry. Fish are the earliest vertebrates to evolve on Earth and gave rise to all subsequent vertebrates; first amphibians, then reptiles, mammals and birds. A sea turtle is a reptile. Reptiles arose after fish, so they cannot give rise to fish. Evolution doesn't go backwards like that. To find the common ancestor of these organisms, you need to go back to early fish, which probably did possess the traits you discuss and passed them onto the modern day fish. So why aren't these homologous traits? Did that common ancestor pass the traits onto the penguin? You answer that question in your post. These traits developed independently in penguins after their more recent ancestors moved from the land back to the sea. As long as at least one of the two species developed the trait independently from the common ancestor, these traits are analogous.
Makes sense. I guess I didn't put together that the sea turtle was a reptile and that reptiles evolved after fish. I should have realized that. It still makes me wonder how fish could evolve into a mammal given the comparatively complex body systems that mammals possess but I'll have to do more reading on this.
DeleteWell it didn't happen all at once! That is the short answer. But don't make the assumption of complexity increasing from fish to mammals. That is a false assumption which trips up a lot of people.
DeleteMany of the same complex systems we possess as humans (digestive systems, circulatory, respiratory, excretory, immune, nervous) exist in fish as well and they have their own unique "complexities" that we don't possess. One of my favorites is the presence of a anti-freeze like substance in the circulatory systems of some fish that keeps their bodies from freezing when temperatures drop below 32 degrees. We aren't lucky enough to have that trait!
Humans may be bigger (though not compared to a great white shark, which is also a fish) and we may have more parts, but the basic systems are not really that different. In fact, there are traits we possess which are really poorly designed compared to other organisms, the result of poor evolution having to tinker its way to an adaptive solution with what ever body parts it has. Bipedalism is a great example of this (would you really stick a bowling ball sized head, containing our most important organ, on top of a skinny neck like ours if you had the choice?). Another example is the human eye, which is actually structured backward, so we have a blind spot in the middle of our vision. The octopus and squid have analogous eyes, developed independently from ours, and they were done right, not backward and with no blind spot. The message here is, don't assume that mammals are more complex or better or more efficient in their design. That is not necessarily the case!
I absolutely love your post about the fruit bat and a humans limb, being homologous. The front limb of the bat (its wing) and the arm of a human. They both do contain the same type and amount of bones and both have five digits. I like how you even point out that even the fruit bat has skin like a human and their body is covered in hair. Though a human and the fruit bat look completely different, they both share the same common ancestor under the class of mammalia. Although they do possess the same trait, their fuctions are dirastically different from each other. Like I said the bat uses their possessed trait in their wings to fly, while a human uses their trait ( arm/ hand) to reach, grab, or push stuff.
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