Homology and Analogy

1. A human and a chicken are two species that possess a homologous trait. A human and a chicken are both vertebrates. Humans are mammals and chickens are birds. They are obviously completely different species. However, they both possess a homologous trait in the forelimb. The function of this trait is used drastically differently in the two species. For example, humans use their forearms for a variety of activities such as lifting or holding, while chickens don't do much with theirs. The structure also appears vastly different from the outside in seeing that humans are long and straight limbed with the ability to bend where chickens are always bent but can extend. Chickens are covered in feathers where humans in skin and hair. However, their underlying construction is similar and directed by a few regulatory genes called Hox genes which makes them homologous. Mutations in these genes led to the variation between species, but they are linked to a common ancestor. The structure is what has been shared by these species because of a common ancestor.

I am not sure as to how to note who the common ancestor between the two species is. However, the ancestor would possess the trait because that is what makes them homologous. The fact that this trait, although different in different species shares a commonality in structure or basic genetic regulations.

2. The Butterfly and the Bird are two species that have analogous traits. A butterfly is an insect while a bird is a vertebrate. A butterfly and a bird both have wings that serve the same function that enables them to fly. Although functionally they are similar, their structure is completely different and that is why they are analogous. Birds are said to have wings that are modifications of the front feet. However, a butterflies' wings are a completely separate appendage. The wing in a bird has an internal skeleton, whereas a butterfly (because an insect) does not. Birds have feathers and butterflies have scales. These two different species can exhibit similarities in these analogous traits because they are a product of separate evolutionary responses to somewhat similar demands that the environment placed on their development of wings.

All living organisms, according to evolutionary theory, share a common ancestor, but because the structure of this trait differes greatly it can be stated that they do not share a closely related ancestor and are not homologous. I think it could be possible that the common ancestor possesses this analogous trait, but because they developed wings independently and are structurally diffeerent I find it too difficult to answer that question indefinitely. I would think that if the ancestor possessed the trait that it would make them homologous.