Vertebrate Evolution Essay Example | Topics and Well Written Essays - 750 words

Vertebrate Evolution - Essay Example The issue of whether a more developed species is advanced or not is subject to how one defines advancement, and is not tackled in this paper because of its subjectivity. Related species usually share similar morphological and or anatomical characteristics. They can either be ancestor-descendant, or descendants from the same ancestor. The proximity of their relation is defined by the amount of evolutionary changes that occurred between them. For example, humans are closer to four-legged animals than to fish. Humans are closer to monkeys than they are to horses because of their opposable thumb. However, not all organisms that have a characteristic in common are closely related. Bats and birds are the only groups of vertebrates that share flight, but bats descended from a lineage of non-winged animals, and are thus more related to humans than they are to birds. Possible relations among groups (A, B and C) can be depicted through a cladogram (Figure 1). Cladistics, the process behind making a cladogram, is usually based on morphology, but can also be made from anatomy or embryology, for example. It is a branching diagram in which the base is occupied by the closest common ancestor. It may be extant, and as such be one of the groups, but it may also be hypothetical, like in this case, and as such is left as blank. From it, a character that differentiates the groups from their closest common ancestor is placed on the branch leading to A, B, and C (tick mark). Because groups A and B are more closely related to each other than to C, the defining characteristic that made them different from C is also placed in the diagram (double tick mark). Points of bifurcation represent hypothetical ancestors. A number of cladograms can be made in relating A, B, and C to one another, but it is usually the tree with the minimum number of evolutionary changes t hat is preferred (Kent and Carr 2004,