4. what is the difference between homologies and analogies

Email Facebook Twitter. Understanding homology and analogy by the Understanding Evolution team In everyday life, people look like one another for different reasons. Biological similarity It works the same way in evolution.

Next The tale of the limb. We can observe that though the shape and the size of the bones are not similar, there is a similarity in their structure that is, they have the same set of bones - humerus, radius, ulna, carpals, metacarpals and phalanges. Man uses his hands to grasp and perform tasks, whales use their flippers for swimming, bats and birds use their wings for flight and horses use their forelimbs for running.

Frogs, birds, rabbits and lizards all have differently shaped forelimbs, reflecting their different lifestyles. But those different forelimbs all share the same set of homologous bones: the humerus, radius, and ulna.

Such homologies reveal the common ancestry of all these animals. Plants too have homologous structures like those seen in animals. Each of these leaves is a homologous structure, derived from a common ancestral form. The pitcher plant and the venus flytrap uses leaves to trap and digest insects.

The bright red leaves of the poinsettia though leaves, look like flower petals. The cactus leaves are modified into small spines that help reduce water loss and protect the cactus from plant-eaters. The tendril of a pea plant and spines of a barberry plant are homologous organs showing similar functions.

The tendril of a pea plant is a modified leaf used for providing mechanical support to the plant. But in the case of barberry plants, the spines are modified leaves meant for protection. The tendril of a pea plant and spines of a barberry though originated from leaves, are homologous organs performing different functions. Analogy refers to the similarity in function of two different organisms due to convergent evolution and not common ancestry. Analogous organs are the opposite of homologous organs, which have similar functions but different origins.

An example of an analogous trait would be the wings of insects, bats and birds that evolved independently in each lineage separately after diverging from an ancestor without wings. Bird wings consist of feathers extending all along the arm. These structural dissimilarities suggest that bird wings and bat wings were not inherited from a common ancestor with wings. This idea is illustrated by the phylogeny below, which is based on a large number of other characters.

Bird and bat wings are analogous — that is, they have separate evolutionary origins, but are superficially similar because they have both experienced natural selection that shaped them to play a key role in flight. Analogies are the result of convergent evolution. Interestingly, though bird and bat wings are analogous as wings, as forelimbs they are homologous.

Birds and bats did not inherit wings from a common ancestor with wings, but they did inherit forelimbs from a common ancestor with forelimbs. Read more about the criteria used in recognizing homologies or how phylogenies are constructed using parsimony. Find additional lessons, activities, videos, and articles that focus on homologies. Building the tree. Using the tree for classification.

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