Homology/Analogy

Week 3 Homology/Analogy Blog Post
by Shira Diamant

1. Homologous Traits

The homologous trait I have chosen is the relationship between the front fins of whales to the bones in the human arm. Human beings are mammals belonging to the primate grouping. Humans use their arms in everyday life for survival, work, everyday tasks and more. Whales are very large marine mammals of the order of Cetaceans. Whales have the general shape of a fish, on a much larger scale. They have forelimbs that have been modified to form flippers, one or sometimes two blowholes used to breathe, and a strong horizontal tail. Whales use their front fins to swim, steer, and survive in the ocean. Many mammals have very similar limb structures. Both the whale and the human have a somewhat large upper arm bone. This bone is known on the human as the humerus. The lower part of the arm limb is constructed of two separate bones. The larger bone, called the radius in human arms, and than opposite that a smaller bone on the other side referred to as the ulna in humans. These species all additionally have a collection of tiny bones in the area around the wrist, which in humans is called the carpal bones. These bones are what lead to the length of the fingers or the phalanges. For humans the arm is slimmer and used to function for the things we need it to do in every day life, from sports, to cooking, cleaning, writing, and more the arm plays a huge role in how efficiently we are able to get tasks done. The whale’s front flipper also has a humerus, radius, ulna, carpals, phalanges and metacarpals. The differences are the scales and shape of the bones proportionally to the body as well as the use of the whale fin in comparison to the human arms. Proportionally, the human humerus bone is longer compared to the whales. The Human radius and ulna are laid out differently in the human as well; possibly because humans have elbows to bend and whales do not. Both whales and humans have five phalanges. The reasons these two mammals have the same overall bones yet a different structure is due to their function and purpose. Whales need their fins to help them swim and steer their large bodies through the oceans whereas humans rely on their arms to help them lift things and complete a large percentage of daily activities. The human arm has more versatility than the whales fin, but they both serve the purpose for which they need to. When researching, I discovered that the whale fin was closely related to cat legs/arms, as well as bat wings. In turn these three mammals were all related back to the general structure of the human arm. When comparing the human arm and the whales front fin it makes sense that a primate would be the common ancestor of the two species considering that is where humans have evolved from. Although this seems far fetch, both whales and humans are mammals and would have a common ancestor somewhere in the mix.

2. Analogous Traits

The analogous traits I have chosen are the wings in both the butterfly and the bird. Birds and butterflies did not evolve from the same common ancestor however they both evolved wings for flight. Birds are warm-blooded vertebrates that lay eggs. They are easily distinguished by their wings, beak and their feathers. Birds use their wings to fly. Butterflies are nectar-feeding insects. They are considered any of the various insects of the order Lepidoptera. They usually have four colorful and broad wings, a smaller body, and knobbed antennae’s. Butterflies, like birds, use their wings to fly. Birds wings are somewhat modifications of their front legs. The birds wings are supported by internal bones than covered in skin, muscles and feathers. They have what we would consider a thumb and first finger, which have significantly reduced in size and are used as claws. The birds have feathers on their forearms, fingers and wrist that form a dome like shape for which air passes once under the wing and than over the top, this vacuum like process is what gives the birds flight. Butterflies wings are very different structurally. Instead of their wings being a modification of their legs, it is an entirely separate body part. The butterfly’s wings are sets of membranes that are stretched between a pair of hollow tubes. The stretched tubes are filled with fluid that comes from the insect’s body cavity. The butterfly is able to use its wings to fly by warming the muscles up and opening them in the direction the sun is. So the butterfly’s wings function as a way of flight and as a solar heater. Also, unlike birds butterflies do not have feathers but beautiful colored scaled that cover their wings. Yes, both birds and butterflies have wings that enable them to fly, however their wings do different things because they are proportionally so different that flight for a butterfly is much different than flight for a bird. The bird and butterfly would not have a common ancestor; they are analogous traits in terms of wings. The bird lineage and the insect lineage developed wings separately and independently from one another. The common ancestor of these two is unknown, however I do believe it is possible that the common ancestor did possess this or a similar trait. Both the butterfly and bird do have wings however the structures are different even though they both use them to fly.