There must be a distinction between resemblances due to propinquity of descent and those due solely to the similarity of function. As previously discussed in the section The Evidence for Evolution: Harmony refers to structural similarities or the correspondence of features in different organisms due to inheritance from a common ancestor. Humans, whales, dogs, and bats all have homologous forelimbs. Because they share a common ancestor with similarly arranged forelimbs, the skeletons of these limbs are all made up of bones arranged in the same pattern.
Analogy refers to the correspondence of features due to the similarity of function that is not related to common descent. The wings of birds and flies are similar. Their wings are not modified versions of structures that existed in a common ancestor but instead evolved independently as adaptations to a common function, flying. The similarities between bat and bird wings are partly homologous and partly analogous. Their skeletal structure is homologous due to common descent from a reptilian ancestor's forelimb; however, the modifications for flying are distinct and independently evolved, and they are analogous in this regard.
Convergent features are those that become more similar rather than less similar as a result of independent evolution. Convergence is frequently associated with functional similarities, such as the evolution of wings in birds, bats, and flies. The external morphology of the shark (a fish) and the dolphin (a mammal) is very similar; their similarities are due to convergence, as they evolved independently as adaptations to aquatic life.
What is Parallel Evolution?
Parallel evolution is another term used by taxonomists. Parallelism and convergence aren't always easy to tell apart. Convergent evolution occurs when descendants resemble each other more than their ancestors did in terms of some feature. Parallel evolution implies that two or more lineages changed in similar ways so that the evolved descendants are as similar as their ancestors were. The evolution of marsupials in Australia, for example, paralleled the evolution of placental mammals in other parts of the world.. There are marsupials in Australia that look like wolves, cats, mice, squirrels, moles, groundhogs, and anteaters.
Because of their adaptation to similar ways of life, these placental mammals and the corresponding Australian marsupials evolved independently but in parallel lines. The similarities between a true anteater (genus Myrmecophaga) and a marsupial anteater (Myrmecobius) stem from homology—both are mammals. Others are similar in that they both feed on ants.
Parallel and Convergent Evolution
The independent evolution of similar traits in different but equivalent habitats is referred to as parallel evolution. It can be found in habitats that are geographically separated but otherwise equivalent. Parallel evolution results in morphological similarities between two species. Because the environmental influences on the species are similar, both unrelated and distantly related species may undergo parallel evolution in equivalent habitats. The figure below depicts various evolutionary patterns.
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Australia's marsupial mammals, which are similar to other placental mammals, are an example of parallel evolution. Marsupial mammals include the wolf, mole, mice, rat, and others. Another example of parallel evolution is the evolution of old and new world monkeys. A long time ago, both old and new world monkeys shared a common ancestor. Despite being separated by the Atlantic Ocean, old and new world monkeys evolve in very similar ways.
What is Convergent Evolution?
The independent evolution of analogous structures in unrelated species is referred to as convergent evolution. It happens when unrelated species coexist in the same environment. As an adaptation to a similar environmental pressure, convergent evolution gives rise to analogous traits in unrelated species. Though the anatomical structure of analogous traits differs, they are functionally similar. For example, despite the fact that North American cactuses (family Cactaceae) and South African euphorbias (family Euphorbiaceae) are from different families, both have thick stems and are succulent as an adaptation to survive in desert regions. The Cactaceae and Euphorbiaceae families are depicted below.
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Another example of convergent evolution is the emergence of wings as an adaptation to flight in birds, bats, and insects. Dolphins and sharks' body shapes have also evolved as a result of convergent evolution.
Despite the fact that dolphins and sharks are distantly related, their body shapes are adapted for fast swimming. As a result, the environment forces distantly related organisms' phenotypes to become analogous. Another example of convergent evolution is the evolution of the eye in vertebrates, cephalopods, and cnidarians. The formation of analogous structures is known as homoplasy.
Similarities Between Parallel and Convergent Evolution
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Evolutionary patterns are classified into two types: parallel evolution and convergent evolution.
In different species, parallel and convergent evolution occur independently.
Under the influence of the same environmental pressures, both parallel and convergent evolution occurs.
Neither parallel nor convergent evolution results in speciation.
Difference Between Parallel and Convergent Evolution
Parallel Evolution: The independent evolution of similar traits in different but equivalent habitats is referred to as parallel evolution.
Convergent Evolution: The independent evolution of analogous structures in unrelated species is referred to as convergent evolution.
Parallel Evolution: Parallel evolution occurs in habitats that are different but equivalent.
Convergent Evolution: Convergent evolution takes place within a specific habitat.
Parallel Evolution: In parallel evolution, two distinct species evolve independently while maintaining the same level of similarity.
Convergent Evolution: In convergent evolution, two distinct species evolve analogous traits.
Convergent Evolution: Convergent evolution occurs in species that are not related.
Parallel Evolution: An example of parallel evolution is the evolution of old and new world monkeys.
Convergent Evolution: An example of convergent evolution is the development of the eye in vertebrates, cephalopods, and cnidarians.