1.
a. Two species which possess a homologous trait are humans and bats. Humans are mammals and a type of primate. Bats are winged mammals; unlike most winged mammals, bats are the only mammals who can travel great distances through flight, instead of gliding for short distances.
b. Just like bats, the human forelimb extends into five digits, or fingers. However, these digit-bones are smaller, thicker, and sturdier than those of a bat. Also the thinner, longer bones of a bat are more curved, and the tissue between them forms a thin, webbed wing, giving them the ability to fly; this allows them to catch prey more easily, as well as escape predators. The function of the human bone structure is to grasp objects and perform tasks which require detailed work and finer movements.
c. The common ancestor of these two species was a reptile, who possessed a very similar bone structure in the forelimbs as both of its offspring.
A human male.
A bat. Notice the similarity of the bone
structure of the wing and that of a human hand
2.
a. Two species which possess an analogous trait are bats and butterflies. Bats, as mentioned earlier, are mammals capable of flight. Butterflies are winged insects, which develop from larvae, or caterpillars; their wings develop from small wing disks found inside the larvae.
b. While bats possess a webbed wing formed from skin stretched across the bones of their forelimbs, butterflies have wings formed by two membranes layered on each other, supported by veins and covered with colored scales. Although the wings of both species serve the same purpose (flight), butterflies have four wings, while bats have only two.
c. The ancestor of these two species did not have wings. Their similar trait, wings, do not resemble each other. If their common ancestor had had wings, the two separate species would have retained the basic wing structure of that ancestor. Yet, because these two species evolved into winged creatures separately due to similar environmental pressures, and not a common ancestor, the structure is very different.
A bat, same as one picture above.
A butterfly. Note the veins in the wings,
wing shape, and number of wings.
Good description and explanation for your homologous trait. For clarification, since both organisms are mammals, the common ancestor would also have been a mammal as well, though you are correct that mammals inherited this common limb structure originally from reptiles.
ReplyDeleteA suggestion: You say "Notice the similarity of the bone
structure of the wing and that of a human hand." It would have been helpful to have an image of the skeleton of both structures to make it easier to see this similarity.
In general, good description and explanation of your analogous traits, but let's talk about the common ancestor. It is possible that the ancestor possessed wings, and then passed them onto the butterfly. But we know that the bat wings are definitely independently derived, correct? Their mammalian ancestor did not possess wings. So aren't these still analogs? As long as the structures evolved independently from each other (and they did), they are analogous, even if the common ancestor possessed wings as well. That is the key to analogous traits, independent (or parallel) evolution.
I think your example of bat wings and bug wings is interesting. The reason is that bugs in comparison to reptiles and animals their structures are totally different! From limbs to eyes, mouths to wings, bugs and mammals have the same traits but done totally different. So their common ancestor must have been a creature that began developing these traits but didn't fully develop them until they were two different creatures.
ReplyDeleteWow, I never really realized that bat wings had any similarity to a human hand let alone the same number of fingers, Very interesting!
ReplyDeleteVery good post. You organize your information very well. I especially found the similarity between the human's hand and a bats wings to be very compelling.
ReplyDelete