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Difference Between Homologous and Analogous Structures
Homologous and analogous structures are two concepts in biology that describe the relationship between the structures of different species. These terms are used to describe how the structures of different species are related to each other and how they evolved over time.
What are Homologous Structures?
Homologous structures are recognisable morphological similarities between closely related animals. In other words, it is not uncommon for closely related species to have homologous features, which are characterised by a similar structure but may serve the same or a different purpose in each case.
Degree of relatedness − When classifying organisms based on their evolutionary relationships, those that have a common ancestor tend to cluster together into what is termed a monophyletic group. When comparing creatures with homologous structures, you may see striking similarities in their embryological growth processes. Comparable similarities exist, for instance, in the embryonic stages of different vertebrate animal species.
Examples from the animal kingdom − Similar architectures may be seen in a wide variety of animal species. The limbs of vertebrates are an excellent illustration of how a common fundamental design may be changed and altered to serve a wide variety of purposes. The arms of a person, a bat, and a bird all include the same three bones—the humerus, the radius, and the ulna—despite the fact that only the bat and the bird have wings. Because of this, the skeletons of certain vertebrate creatures are adapted for flight, whereas those of others are employed for locomotion.
Examples from the plant kingdom − Several plant leaves are instances of homologous structures found in nature. Several plants' leaves evolved from the same ancestral design, but different adaptations have allowed some to store water (like cacti) and others to capture insects (e.g. Venus fly trap and pitcher plant).
What are Analogous Structures?
While the external appearance of structures that provide similar functions in various organisms may imply that they have a common structure, this is often not the case.
Degree of relatedness − The degree of relatedness dictates that a phylogenetic tree would not be monophyletic if it included organisms with similar features but which were not closely related and so did not have a common ancestor. Instead, comparable structures in other organisms served the same or a similar function by independently evolving. While the structures are not identical, they serve similar purposes in different creatures, such as flying.
Convergent evolution can provide structural similarities; for example, both squid and fish have streamlined bodies for easy swimming. When creatures from various areas of the world exhibit the same morphological adaptations to environmental circumstances, this is an example of convergence in evolution.
Examples from the animal kingdom − The wings of birds and the wings of insects are only two examples of similar structures seen in the animal kingdom. Bird wings are made of hollow bones derived from early chordate ancestors. Insect wings developed independently of gill structures in early insects that spent much of their lives in water.Examples from the plant kingdom:
In the plant kingdom, euphorbias from Africa have succulent leaves like cactus from the New World so that they can store water. Nonetheless, these plants' modified storage leaves are an example of convergent evolution since they developed independently from two different ancestor plants. The leaves of euphorbias and cacti, then, serve the same purpose yet evolved separately.
Differences: Homologous and Analogous Structures
The following table highlights the major differences between Homologous and Analogous Structures −
Characteristics |
Homologous Structures |
Analogous Structures |
|---|---|---|
Definition |
Homologous structures are structures that evolve in living organisms that have a common ancestor. |
Analogous structures are those that evolve independently in different living organisms but have a similar or the same function. |
Degree of relatedness among organisms |
Organisms which have homologous structures are always closely related and share a common ancestral form. |
Organisms which have analogous structures are not closely related and do not arise from the same ancestor. |
Developmental pattern |
The developmental pattern in organisms which have homologous features tends to be very similar, and this is often evident when examining the embryos of these organisms. |
The developmental pattern in organisms which have analogous features tends to be very different. The developmental pattern in organisms which have analogous features tends to be very different. |
Functions |
Homologous structures may serve the same or different functions. |
Analogous structures always have the same or very similar functions. |
Animal examples |
The limbs of vertebrates are examples of homologous structures, and in fact the same bones are present, yet modified from one animal to another. |
The wings of insects and birds are examples of analogous structures with completely different evolutionary paths and origins. |
Plant examples |
Examples of homologous structures are the modified leaves of the pitcher plant, Venus fly trap, and cactus. |
Examples of analogous structures include the leaves of African euphorbia and cacti. |
Conclusion
Homologous and analogous structures are two concepts in biology that describe the relationship between the structures of different species. Homologous structures have a common ancestry and have evolved from a shared ancestor, while analogous structures serve the same function in different species but have different ancestries.
Understanding the difference between these two concepts is important in understanding the evolutionary relationships between species and the history of their evolution.
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