Homologous Structure Research Paper

Aspects of anatomy that may appear different in two animal groups, however demonstrate a similarity that would be consistent with the presence of a common ancestor are referred to as homologous structures. These structures are similar in position, structure, and evolutionary origin, but often differ in function. These homologous structures can be used as clues in piecing together the puzzle that is evolutionary lineage. These homologous structures demonstrate how a limb or other body part can adapt to suit various evolutionary needs. This is a mechanism of divergent evolution: the evolutionary diversification of organisms from a common ancestor.
On the outside, a bird’s wing looks almost nothing like a human forelimb. The wing is covered in
It also appears that the dog has a sort of second elbow. Human feet are considered plantigrade, which means the heel (plantar) is normally in contact with the ground, along with the balls of the feet and the toes. This arrangement is ideal for balance, but is typically slow. This is the reason that humans are natural distance runners. For animals that need more speed, less surface area in contact with the ground is better for fast movement. Dogs adapted to chase fast prey (e.g. elk, deer, hares, etc.) and so have evolved to walk and run on the balls of their feet. This is referred to as digitigrade motion, in which the heel does not typically contact the ground. This is less balance oriented, however is favorable to plantigrade for speed. As the dog’s heel is not in contact with the ground, it creates the appearance of a second elbow, oriented in a way that is unfamiliar to our own anatomy. Though these limbs appear quite different, the skeletal structure is very similar with a few modifications, such as the grade of digital locomotion. Figure 2 demonstrates side-by-side a dog and human leg, in which the homologous bones are labeled between the two