[Biology Class Notes] on Comparative Anatomy Pdf

The study of the similarities and the differences in anatomy, i.e. the body structure of two or more species is called comparative anatomy. This study of comparative anatomy in biology is essential to understand the areas of variations that gave rise to some evolution. And to compare present organisms with prehistoric organisms, biologists and scientists use the fossil evidence left behind, to witness the occurred evolution. Evolution is a genetic change that occurs in a species of a particular area over a long time. Evolution occurs in organisms for helping them to survive in the environment. During this shuffling of genes, it results in the development of a new trait and helping the animal to survive in the environment.

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Comparative Anatomy Definition

To define comparative anatomy, we can say that it is comparative studies of the anatomy of different animal species to understand the course of evolution from their common ancestors by analyzing the undergone adaptive changes.

Comparative anatomy was used by early evolutionary scientists like Lamarck and Buffon for determining relationships between different species.   

Analogous Structures

In different organisms, the same or similar structures are called analogous structures. The analogous organs serve similar functions, but they have different origins and are entirely different in their organization. For example, the wings of the birds and that of the insects perform the same task, i.e. wings in both organisms are used for flying, but they have a dissimilar origin. The structure of birds’ wings is very similar to the forelimbs or hands of humans, but this structure of wings is very different from the structure of insects’ wings. The wings of birds and the wings of insects are analogous structures which have emerged because of convergent evolution.

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Homologous Structures

In the vertebrates, some specific organs or structures have similar structural organization origin but have different functionality, are called homologous structures. For instance, the forelimbs of bats, horse, birds, and whales have a similar structure and same origin, but they all serve different functions. Forelimbs of bats are used for gliding in the air, and that of birds are used for flying. The forelimbs of the horse are used for running on the ground, and the forelimbs of whales which are called flippers are used for swimming. All these homologous structures in the vertebrates are used for different purposes but have a similar structural organization.

The same developmental history of the homologous organs can be identified when homologous structures are analyzed internally to find that all these organs contain bones like humerus, ulna, radius, phalanges, etc. and other associated muscles. Based on comparative analysis of homologous structures, supportive evidence is obtained in favour of biological evolution.    

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Solved Examples

The examples from the vertebrates’ structures of comparative anatomy provide evidence for evolution.    

• In all vertebrates, the heart consists of chambers called ventricle, auricle, conus arteriosus, sinus venous, etc. The arrangement of the chambers in hearts of the vertebrates is essential for providing partition. The chambers work as the prevention for the mixing of oxygenated and deoxygenated blood. In the heart structure of vertebrates, an evolutionary change is observed, such as the single-chambered heart of the fishes gradually evolved to form the hearts of other organisms suitable to their environment and necessity. The heart of amphibians and reptiles, which are three-chambered, whereas the hearts of mammals and birds are four-chambered.

• In all the vertebrate organisms, the vertebral column originates from four mesodermal masses in each somite. The vertebral column consists of vertebrae, each having a centrum, neural canal, neural arch, neural spine, articular processes, and the transverse processes.

• Progressive evolutionary changes are observed in the anatomy of the brain in different vertebrates. The brain of almost all vertebrates consists of similar five parts which are called the five lobes of the brain, and they are the Olfactory lobes, Optic lobes, Cerebral lobes, Cerebellum and Medulla oblongata. The anatomical changes that occurred in the brain of different vertebrates are like the cerebral hemisphere in mammals is much larger than that of in fishes. In contrast, the olfactory lobe of the fishes is much larger than mammals.

Did You Know?

The organs present in some animals (especially in higher vertebrates) which are non-functional and rudimentary are called vestigial organs. The animal once used these organs because of the then lifestyle, but in due time with the changes in the environment, these organs became unnecessary and lost its use. Vestigial organs provide supportive evidence in favour of evolution. Examples of vestigial organs are the vermiform appendix and the muscle in the outer ear in humans. But these same organs are useful in lower mammals. Like the vermiform appendix is associated with helping herbivores with digestion. In smaller mammals, the use of ear muscle is for assisting them in moving their pinna in different directions.