Homologous and Analogous Traits

1. For your homologus traits provide the following information (25 pts):

homologous trait: human forelimb and bottlenose dolphin pectoral fin.

a.  Briefly describe the two different species that possess the homologus trait. (5 pts)

            Humans are hominid primates. They are distinguished from other primates by several factors: a larger brain with more developed areas (which enable advanced levels of logic, reasoning, linguistic communication skills and creativity), locomotion that is exclusively bipedal in adults, etc. Humans are in general omnivorous.

            Dolphins are marine mammals of the order Cetacea (there are many different families and genera). They are carnivores (living mostly off of fish and squid), and can be found worldwide, generally in shallow rather than deep waters. For my purposes, I will compare the fin of the bottlenose dolphin, of the family Delphinidae and the Genus Tursiops. Research indicates that bottlenose dolphins are quite intelligent; according to National Geographic, they “…travel in social groups and communicate with each other by a complex system of squeaks and whistles.” (http://animals.nationalgeographic.com/animals/mammals/bottlenose-dolphin/)

b. Describe the homologus trait of each species, focusing on the differences in structure and function of the trait. Why do these homologus traits exhibit differences between the two species? Make sure your explanation is clear and complete. (10 pts)

            Human forearms are comprised of many bones, including the humerus, radius, ulna, metacarpals and carpals, which allow for relative flexibility and the ability to grasp objects with an opposable thumb. Dolphin pectoral fins, on the other hand, aid in swimming through water by allowing the dolphin to stop, turn, and balance effectively; pectoral fins do not have opposable thumbs and thus do not aid in grasping objects. In the same way, human hands are not as useful for swimming as are dolphin pectoral fins. Therefore, although the bones of the two organisms appear similar structurally, the function of the limbs has evolved to be entirely specialized to the environment in which the respective organisms thrive.

c. Who was (generally, not specifically) the common ancestor of these two species and how do you know that ancestor possessed this homologus trait? (5 pts)

            Interestingly, dolphin pectoral fins are the only fins to contain bones, and the bones resemble the human arm in some respects. Thus the two species must have shared a common ancestor. The common ancestor of dolphins and humans must have been a land mammal. The ancestor of dolphins probably entered the water during the Eocene epoch, about 50 million years ago. Since then: “Evolving in water over time, dolphins became more streamlined and lost their hind limbs in favor of tails that enable them to swim faster and dive deeper after prey.” (http://marinebio.org/oceans/dolphins.asp) Because the bones in the pectoral fins of dolphins are largely vestigial, and the land mammals humans have retained the arm structure, then the two can be traced back to a common land mammal ancestor.

d. Provide an image of each species in this comparison. (5 pts)

2. For your analogous traits provide the following information (25 pts):

The wings of a monarch butterfly and the wings of a common vampire bat.

a. Briefly describe the two different species that possess the analogous trait. (5 pts)

            North American monarchs migrate in huge numbers to California and Mexico every winter—they are the only butterflies that do this. Monarchs go through a life cycle: monarchs are born as eggs that hatch into larvae, which eat the milkweed plants on which they were born. They then turn into plump caterpillars, which create a hard protective case around themselves, and go into the pupa stage. Eventually the emerge as the iconic monarch butterfly. (http://animals.nationalgeographic.com/animals/bugs/monarch-butterfly/)

            Bats in general are the only mammals that have the capacity to fly, and vampire bats are the only mammals that subsist entirely off of blood. Bats sleep during the day in darkness, and suspended by their feet from the ceiling of a cave or cave-like structure. They hunt at night. (http://animals.nationalgeographic.com/animals/mammals/common-vampire-bat/)

b. Describe the analogous trait of each species, focusing on the similarities in structure and function of the trait. Clearly explain why these analogous traits exhibit similarities between the two species. (10 pts)

            The analogous traits, the wings on both the butterfly and the bat, allow the creatures to fly by generating lift. They both are wide, in general much larger than the organism’s body;  when seen head-on, the outwardmost point of the wing is generally higher or about level with the organism’s head. Both creatures require flight to feed and get around effectively, and thus in both cases wings are advantageous for the survival of the individual organism and its reproductive success.

c. All pairs of organisms share some common ancestor if you go back far enough in time. Did the common ancestor of these two species possess this analogous trait? Why or why not? (5 pts)

            Most likely the common ancestor did not possess the trait of wings, because, for bats at least, wings developed after the evolution of forelimbs, and that would have been much later than the divergence between mammals and insects. Therefore, because wings developed later temporally than the split between insects and mammals, the analogous trait was not possessed by a common ancestor.

d. Provide an image of each species in this comparison. (5 pts)