[Biology Class Notes] on Analogy Evolution Pdf

Here we will understand how to define analogy. The analogous structures and homologous structures are used to study the course of evolution. The study of these structures comes under the field of morphology. Under morphology, we study the external structures of an organism and also about their functions in the organism. On the other hand, anatomy refers to the study of the internal structures of the organism and its study of function. From the beginning of the universe, there are a lot of organisms that are present on the earth and they all are of a very diverse nature. So to make our study of these organisms easier we started classifying them under similar characteristics. The analogous and homologous organs help us to understand and characterize certain sets of organisms under each other. Also, the study of analogous and homologous structures gives us evidence of evolution. After making our studies we can compare their morphology and anatomy and this can surely give us an edge in studying these organisms and also the evolution. The study of analogous and homologous organs is termed an understudy of evolutionary relationships. This helped us to define analogy and further, we will learn about an example of analogous organs. 

Evolution of Analogous Structures and Analogous Organism

These structures are not anatomically similar. This means that they are made up of different parts of the body but they serve the same purpose. These structures are different in different organisms but they share or perform similar functions. This also means that externally these structures may not look similar to each other. This property when the structures are showing analogous nature is known as an analogy. Also, it is seen from the studies that the analogous structures do not have common ancestry but these structures are placed under the same group because of their similarity in performing similar functions. This gives us a clear answer to our question of how do analogous structures evolve. Now we will learn about some analogous structures examples.

• Wings of Butterflies and of Birds: This is one of the example of analogous organs. We know that birds have a vertebral column so they are vertebrates and butterflies do not have vertebral columns so they are invertebrates. But they both have wings and their wings perform the same function that is flying. But when we look closely, their internal designs and the components from which both wings are made are very different. This shows or gives us an understanding that these structures are evolved differently but as they serve the same purpose, so they are showing convergent evolution. This is because of the adaptations that they need and also the presence of similar habitats. So this can be concluded from this example of analogous organs that these structures have evolved from convergent evolution. 

• Eye of Octopus and Eye of Mammals: The position of the retina in the eye of the octopus and the eye of the mammals different and this makes them different internally but these both serve the same purpose of vision.

• Flippers of Penguins and Dolphins: Penguin is a bird whereas the dolphin is a mammal. Both of these organisms have the presence of flippers. They are different in internal structures but they serve a common purpose that is helping in swimming. 

• Sweet Potato and Potato: Potato is a modified stem and sweet potato is a modified root. They have originated differently but they serve the same purpose of storing food. 

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Homologous Structures

After giving an answer to define analogy and also learning about analogous structures in a sentence, now we will learn about homologous structures. These structures are different from analogous structures. These structures have similar anatomy but they have different functions. A very good example to explain it can be seen when we study the structure and function of forelimbs in mammals. Let us take some examples such as man, cheetah, whale, bat. In all these four organisms the structures are evolved from the same line of evolution. They are made from forelimbs. But they serve different functions such as in man forelimbs are used to hold things, in cheetah they are used for running, in whales they are used for swimming and in bats they are used for flying. So this way we can see that the homologous structures have evolved from the same course of evolution but they serve different purposes. We can get to the conclusion that the homologous structures are a result of divergent evolution. Some more examples are:

• Vertebrate Heart and Brain: The basic plan of the heart and brain in almost all organisms is the same but their complexity and varied degree of specialization make them different from each other. 

• Thorn of Bougainvillea and Cucurbita: They are made from the same course of evolution but one has developed as a thorn and the other has become a tendril.