These are called analogous structures. Since these structures are so different, even though they have the same function, they do not indicate an evolutionary relationship nor that two species share a common ancestor.
For example, the wings of a bird and dragonfly both serve the same function; they help the organism to fly. However, when comparing the anatomy of these wings, they are very different. The bird wing has bones inside and is covered with feathers, while the dragonfly wing is missing both of these structures.
They are analogous structures. Thus, by comparing the anatomy of these organisms, scientists have determined that birds and dragonflies do not share a common evolutionary ancestor, nor that, in an evolutionary sense, they are closely related. Another type of evidence for evolution is the presence of structures in organisms that share the same basic form.
For example, the bones in the appendages of a human, dog, bird, and whale all share the same overall construction [Figure 2]. That similarity results from their origin in the appendages of a common ancestor.
Over time, evolution led to changes in the shapes and sizes of these bones in different species, but they have maintained the same overall layout, evidence of descent from a common ancestor. Scientists call these synonymous parts homologous structures. Some structures exist in organisms that have no apparent function at all, and appear to be residual parts from a past ancestor. For example, some snakes have pelvic bones despite having no legs because they descended from reptiles that did have legs.
These unused structures without function are called vestigial structures. Other examples of vestigial structures are wings on flightless birds which may have other functions , leaves on some cacti, traces of pelvic bones in whales, and the sightless eyes of cave animals.
Click through the activities at this interactive site to guess which bone structures are homologous and which are analogous, and to see examples of all kinds of evolutionary adaptations that illustrate these concepts. Another evidence of evolution is the convergence of form in organisms that share similar environments.
For example, species of unrelated animals, such as the arctic fox and ptarmigan a bird , living in the arctic region have temporary white coverings during winter to blend with the snow and ice [Figure 3].
The similarity occurs not because of common ancestry, indeed one covering is of fur and the other of feathers, but because of similar selection pressures—the benefits of not being seen by predators.
Embryology, the study of the development of the anatomy of an organism to its adult form also provides evidence of relatedness between now widely divergent groups of organisms. Structures that are absent in some groups often appear in their embryonic forms and disappear by the time the adult or juvenile form is reached. Measure content performance. Develop and improve products. List of Partners vendors. Share Flipboard Email. Heather Scoville. Science Expert. Heather Scoville is a former medical researcher and current high school science teacher who writes science curriculum for online science courses.
Featured Video. Cite this Article Format. Scoville, Heather. Anatomical Evidence of Evolution. Anatomy, Evolution, and the Role of Homologous Structures. Glossary of Terms Regarding Evolution. Tips on Winning the Debate on Evolution. Gradualism vs. Punctuated Equilibrium.
Your Privacy Rights. Note that homologous structures don't have to have the same function. For example, a human arm and a whale flipper are used for completely different purposes but are made of very similar bones. They are homologous to each other. Physiological evidence of evolution deals with the functions of body parts among different species. Analogous structures are body parts of different species that have a similar function.
These structures have a similar purpose but can look completely different. Vestigial structures are also useful to observe. These are structures found in the body that no longer serve an important function.
The human tail bone is an example. It suggests that humans evolved from a species that had a tail. The wings of a butterfly and the wings of a bat have the same function, to fly. However, the structures look nothing alike. Similar function does not mean that two species have evolved together. If the function is the same but the structures are not similar, then there probably is no recent common ancestor. Analogous structures are important because they show how similar functions evolved independently among different species.
Convergent evolution is the process by which different species independently evolve analogous structures because they have to adapt to similar environments. The anatomical structures and physiological functions of different species provide evidence of evolution. Scientists compare and contrast types of anatomical features, known as homologous structures, vestigial structures, and analogous structures, to figure out how closely related different organisms are.
Homologous structures are parts of different species that originate from a common ancestor. For example, all vertebrate limbs have the same general structure but are used in astoundingly different ways.
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