A comparison of the anatomy of different species of animals reveals significant anatomical similarities, clearly indicating their evolution via divergence from one or more common ancestors. Biologists have recognised three categories of structures based on similarities in the structure and function of organs and organ systems in various organisms: homologous, analogous, and vestigial.
Homology studies structures in different related species resulting from a shared ancestor, often expressed in a common embryological origin. These structures, known as homologous organs, result from various evolution and allow organisms to perform distinct roles. Vertebrate forelimbs are an excellent example of organs with identical anatomy but diverse function.
Metameric animals exhibit a unique sort of homology, such as arthropod appendages. Homology results from adaptive radiation from a common ancestor, allowing organisms to adapt effectively to varied ecological niches. The anatomy of a mammalian forelimb is a famous example of adaptive radiation. The upper arm always has a single long bone. The humerus, the ulna and the radius are two parallel bones of the forearm, and the carpal bones are usually organised in two rows of four in the wrist.
Five parallel metacarpals form the palm, and the skeleton of the digits is formed by rows of three phalanges apiece, except for the first digit, which has only two phalanges. Tenrecs (scaly ant eaters) of the order Insectivora have rudimentary pentadactyl arms. All limb bones are short and wide, giving the limb a shovel-like look.
The humerus, radius, ulna, and four fingers are considerably enlarged in Chiroptera bats to support the wing membrane. The humerus is short and heavy in ungulates like the horse, designed for running or a cursorial habit. Adults frequently experience bone fusion. The forelimbs of aquatic animals, such as whales, are transformed into flippers to help in swimming. Plants can also have homologous structures, demonstrating that the core pattern remains consistent.Plants can also have homologous structures.
For example, a homologous thorn in a bougainvillaea, a rose, and a tendril in the cucurbits, emerge in the axillary position. There are several examples of this, demonstrating that, despite a wide range of variance, the core pattern remains consistent. All taxonomic group members are built on a standard plan, with variances among members that fit each to its manner of existence. The larger the variety, the higher the taxonomic category.
Since Darwin, most biologists have held that tight anatomical likeness must be founded on close genetic kinship and that more distant resemblances represent the more distant genetic relationship.
Analogous organs are physically distinct structures that emerge in various unrelated creatures to perform similar activities. However, these structures share some commonalities based on modifications to accomplish the same activities. These organs, known as homologous organs, result from convergent evolution.
The set of wings developed separately by insects, certain extinct reptiles, birds, and bats are famous examples of homologous organs. An insect wing is a membrane held together by chitinous veins. The wing is a dead structure powered by muscles linked to its base. Pterosaurs, prehistoric flying reptiles, had wings of a fold of skin supported by a massively expanded fourth forelimb finger.
The planing surface of a bird's wing is made up of feathers. The feathers are held in place by an internal skeleton of forelimb bones. A bat's wing is created by a membrane adapted from the skin. The bat's wing is supported by the enlarged and outspread phalanges of the last four forelimb fingers. Tendrils are one example of tendrils in plants. Pea and vine tendrils have distinct origins. The first is a modified leaf, while the second is a modified stem. Other examples from plants and animals demonstrate that apparent resemblances are the product of adaptive adaptations in response to identical environmental circumstances.
Studying vestigial or rudimentary organs is another significant component of comparative anatomy. The presence of vestigial organs adds to our understanding of speciation through evolution. The relics indicate structures previously beneficial to the progenitors but were transformed in the development process in the descendants. Such changes occur during evolution due to adaptations to changing environmental circumstances. In many situations, the diminished organ has taken on a new role, unlike the one for which it was initially designed. In other circumstances, it is pointless.
The human vermiform appendix is the most well-known relic. It is a little structure that looks wormlike (vermiform) and is the constricted terminal section of the large intestine's caecum. The caecum and appendix are significantly more prominent in certain mammals that feed on a coarse fibrous diet high in cellulose. This allows the microorganisms trapped there to break down the cellulose enzymatically.
However, the appendix has been deemed redundant in humans with altered dietary habits (lower cellulose consumption) and remains rudimentary. It can be a source of discomfort when it enlarges and causes appendicitis. In humans, it may be removed surgically without causing any harm.
Other examples of vestigial organs in animals and plants abound. In animals, examples include the nictitating membrane of the eye, the external ear muscles, and the wisdom teeth in humans, the vestigial caudal vertebrae (embryonic tail) in higher primates, the pelvic girdle in whales, boas, and pythons, and degenerated eyes in cave-dwelling vertebrates and invertebrates. Plant vestiges include concealed stomata on cactus stems, vestigial leaves in prickly pears, abortive stamens in Labiatae, and abortive pistil lodes of male flowers Cucurbitaceae.
Similarly, in particular members of the Compositae family, the ray florets contain an abortive pistil devoid of any stigma and hence do not pollinate. As a result, the ovules are abortive.
Comparative anatomy provides evolution evidence through homologous, analogous, and vestigial organs. Homologous organs result from evolution and allow organisms to perform distinct roles, while analogous organs result from adaptive radiation from a common ancestor. Comparative anatomy focuses on the evolution of forelimbs, homologous, vestigial, and vestigial organs.
Analogous organs are physically distinct structures that emerge in unrelated creatures to perform similar activities, while vestigial organs are adaptive adaptations to identical environmental circumstances. Vestigial organs are relics of structures previously beneficial to progenitors but have been transformed due to adaptations to changing environmental circumstances. Examples include the human vermiform appendix and other animals and plants.
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