Thursday, February 26, 2015

Analogy/Homology

1. Homologous Traits

a. A human arm and horse’s front leg possess homologous structures.

b. The human arm and horse’s front leg have the same number of bones.  They also have the same arrangement. Each has a humerus, radius, ulna, carpels, metacarpals, and phalanges. Humans require both bones and muscle to coordinate in order to complete gross and fine motor movements.   Horses front legs bones are connected, which allows the horse to bend and lift their leg for movement.


c. The common ancestor of the horse and humans is the dinosaur. Humans and horses share forelimbs.  They both have protective membranes surrounding their fetuses. The membrane protects the egg while in humans, horses, and hard-shelled alligator eggs.  This is why I believe they are common ancestors.


d.  




2. Analogous Traits

            a. Two different species that possess analogous traits are the owl
            and the butterfly.

b. The analogous trait for owls and butterflies is they both have wings.  Butterflies have two pairs of wings, while owls have one pair.  Butterfly wings do not have bones but owl wings do have bones.  Owl wings have feathers while butterfly wings are bare.  Both butterflies and owls have adjusted to life in the air and in doing so, have changed their wings.  Their wings have evolved independently in each of group and do not indicate that they are closely related.

c. The insect wing and the tetrapod wing did not exist when the insect and tetrapods last shared a common ancestor.  Their respective wings evolved independently of each other after they have become separate evolutionary ancestries. Butterfly wings and owl wings are analogous structures because they evolved independently of each other from different precursors.

d.  

                       



5 comments:

  1. I like how detailed and interesting this post was. It never crossed my mind that horses and humans had a common ancestor, and I certainly would have never guessed that it would have been dinosaurs. I thought it was a very good example.

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  2. I liked your comparison on the human and horse bone structure. but i think it would be better if you explained more about how the horse structure functions and why. For example the horse hands or fingers evolved from five down to one, because its a better fit for its size and helps it in its locomotion.

    The analogous sections was another great comparison in the owl and butterfly wings great job.

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  3. Adam, Thank you for your comments.
    Steven, I appreciate your feedback and will keep in mind more detail in future posts.

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  5. Part A in both sections for descriptions of organisms, not just identification. Expand.

    "The human arm and horse’s front leg have the same number of bones."

    While I understand your point, the horse has far fewer bones as it is missing all of those extra carpals, metacarpals and phalangies that humans have.

    "Horses front legs bones are connected."

    I'm afraid I don't understand this. Human limbs and horse limbs are all put together with the same materials: Bones, ligaments, tendons, cartilage and muscle. Both allow for movement at the joints though from that point on, they do serve very different functions. Yes, humans emphasize fine motor movement in their hand but they also require strength actions in their arms. The key difference perhaps is that the horse's leg is for locomotion and support. That function is missing in humans. So how do the two structures differ based upon these differences in function? What differences do you see in the bone structure of these two limbs (and my comment on the fewer bones actually is a hint!).

    With regard to ancestry, both humans and horses are mammals so their common ancestor was an archaic mammal. (Yes, mammals arose from reptiles, but not dinosaurs reptiles ... there is a difference!). This common mammalian ancestor possessed the general mammalian limb structure and passed it down to these two descendents, resulting in the different structures we see today. That evidence of common descent is what we need to confirm that these traits are indeed homologous.

    Good description of your analogous pairing, though again the description of the organisms was short on detail.

    "The insect wing and the tetrapod wing did not exist when the insect and tetrapods last shared a common ancestor. "

    That is perfectly stated. That is all we need to know that these structures arose independently though convergent (or parallel) evolution and not through common descent. Well done.

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