Homologous Traits
A. Even though a human (photo on the left) and a bird (photo on the upper right) seem as if they have don’t have anything in common, they actually do. As you can see in the photo on the right a human has the same exact bones in their arm that a bird has in their wing, meaning that they have homologous traits. Even though humans are mammals that live with their feet on the ground and birds are covered in feathers and can fly in the air, they are still similar.
B. Both humans and birds share the same bones including: Humerus, carpals, metacarpals, radius, ulna, and phalanges. Even though humans and birds have this homologous trait, the way they evolved has created some very easy to see differences. As you can see even though humans and birds have the same bones they do not possess the same limbs. Humans have arms, hands, and fingers so they can grab, reach, and even drive a car. While bird’s bones have evolved so that they can fly in the air.
C. Although we do not know who the common ancestor of humans and birds actually is, scientist have come up with a general idea of what species both birds and humans have derived from. A team of scientist have been able to gain a large amount of information about the species. It has been concluded that both species had evolved from a small creature that lived off of insects. (pictured on the right)
Analogous Traits
- Even though ducks(left) and platypus(right) share a lot of similar traits with each other, one is a mammal (platypus) and the other is a bird (duck). They both have bills, lay eggs, and have webbed feet, etc. As you can see in the two photos above a platypus basically looks like a cross between a duck and mammal making it seem as if they were related but in the end are from different ancestors.
- One analogous trait between ducks and platypus is webbed feet. Even though both species possess webbed feet, platypus are able to retract the webbing on their feet so that they are able to burrow into the ground to nest and lay eggs. Ducks however are not able to retract the the webs on their feet making it impossible for them to burrow causing them to nest and lay eggs above ground. Even though there are differences between both of their feet they both still have the need to swim which is why they have both developed webbed feet.
Okay on your description of homologous species pairings, though this section was for description of the species in general, not just their traits. That was for the next section.
ReplyDeleteIn general, good discussion of the differences in function for these forelimbs. Yes, I do see the differences in structure from your images, but can you explain those differences and how they relate to function? Your image choice was great, but it would have helped to have a written explanation to go along with it.
With regard to ancestry, we actually know quite a bit more than this, and we can take that information to confirm that these traits are homologous, which is the goal of this section. Humans are mammals, who arose from reptiles. Birds arose from reptiles as well, so the common ancestor between humans and birds would be an archaic reptile.
We know from fossil evidence that the common reptilian ancestor possessed the primitive forelimb structure and passed that trait onto these two descendants with variation arising due to different environments and functions. That is what we need to know to confirm that these are homologous traits.
Good description of your analogous species pairings.
Good discussion on your choice of webbed feet as your analogous trait. It is a little more difficult to follow this trait as it doesn't fossilize well, but we do have quite a lot of information on this trait.
Though you mention "ancestors" in the first section, you don't include a final section explaining how to use ancestry to confirm that these traits are indeed analogous. For example: Ducks are birds and the platypus is a mammal. Both share a common reptilian ancestor (just like the human bird pairing in the homologous section). Ducks developed their webbing when they split from non-aquatic birds to move into an aquatic environment. Likewise, the platypus evolved its webbed feet after it split from the mammal line and moved into an aquatic environment. This means that in both cases, webbed feet evolved *after* that divide at the common ancestor. That means the trait arose independently in both cases, which is what we need in order to confirm that these traits are analogous traits.
Good images.