Analogous Structures

The structures which perform same function, but have different evolutionary history are called analogous structures and also known as convergent structures. For example, wings have same function for insects and birds, but there is no evolutionary similarity between these wings. You may find some structures look totally different, still they are homologous. Some seem homologous, but actually they are not. Wings of birds and bats look similar in structure though they evolved independently, but are related to each other because they adapted to similar environment and this process is known as convergent evolution. Analogous traits are adopted due to convergent evolution. Let's take another example to understand it, the tusks of elephants and the gnawing front teeth of the beaver, both are incisor teeth. They have been inherited from common ancestors, but modified with due course of evolution according to the respective uses and now look very different from each other.

Animal kingdom has many examples of convergent evolution. In birds, both new and old world vultures look very similar, both have featherless necks and heads and feed on carrion. But something amazing has been discovered about them. These two species look similar, but belong to different families. Old vultures belong to eagle's family whereas new world vultures belong to stroke's family. Old vultures use eyes to find food whereas new vultures use both olfactory senses and sight to search food.

Do not confuse analogy with homology. Analogy is quite different from homology where the structures are similar because they have common embryonic origin. Let's take some more examples to understand it in a better way.

Examples of Analogous Structures

• Limbs of tetrapods and arthropods are analogous to each other. The limbs of arthropods evolved after the Cambrian explosion, more than a billion years ago. Tetrapods evolved from fish somewhere around 370 million years ago. Thus, the limbs of arthropods and tetrapods were independently evolved.
• The legs of vertebrates and insects serve the same purpose, but they have different structure and evolutionary history. They have come from two different origins.
• Another example is plant leaves and Ruscus's cladodes. Both of them are used for carrying out the process of photosynthesis, but have different origin.
• Sweet potato and potato have the same function that is, modification for food storage, though sweet potato is underground tuberous root and potato is underground stem. They have different structure and origin, but serve the same purpose.

There are many reasons because of which the animals in the nature resemble each other. Two insects of the same species might look similar because of the same color of spots inherited from the ancestors. Even a bat and a bird also appear similar because of their wings. Human beings, lizards and whales have similar skeleton structure although they have different habitat and lifestyle. You can see the similarities in their skeleton structure, still human beings use their limbs to throw a ball, whales use fins to swim and lizards use their limbs to climb the wall. Each one of them are similar in structure, but different in details. Evolutionary biologists call these structures analogous.

These ongoing process of evolution can be traced with the help of comparative anatomy. Several other evidence can be studied with the help of bio-geography, the fossil records and the molecular records. Analogy is an aspect of evolutionary biology which says that the structures are similar not because of embryonic origin, but due to similarities in function. Analogies evolve when the challenges and problems faced by two species are similar. Evolution then shapes both as similar and thus, their structures are evolved.