Homologous vs Analogous organs

homologous vs analogous

Introduction

In ancient times, people used to think that the world had not changed. There is no such concept of evolution and origin. In the fifth century, BC Xenophane discovered some fossils and showed that there is a difference between the past and present organisms. In the fourth century BC, Aristotle proved that there are different classes in the living world and that one class of creatures is superior to another. Organisms have evolved from their ancestors to their present form. This evolution did not happen suddenly the change has taken place over billions of years. Evolution refers to the development or change of something in a natural way. Today biologists believe in evolution and there are various theories about how evolution took place. There is much evidence that favors evolution, among this evidence, anatomical evidence is important evidence. Anatomical evidence, homologous vs analogous organs are former have the same origin but different function while later have same function but different origin. are discussed below (1) & (2).

Homologous organs

Definition

Organs of an organism that are similar in origin and structure but functionally different are called homologous organs. The origin and structure of homologous organs are the same but their external structure and activity are different due to their adaptation to different environments. This type of evolution of homologous organs in different environments is called divergent evolution (2).

Example

Wings of birds, limbs of horses, flippers of whales, limbs of dogs, human hands, etc. are examples of homologous organs (4).

Homologous organs of animals

A comparison of the pelvic, forelimb, hind-limb bones of different vertebrates shows that the basic structure of the bones of all those organs is the same. For example, the wings of a bird, the forelimb of a dog, the forelimb of a horse, the human hand, the paddle of a whale, etc. are all homologous organs.

Although the external structure of the organs is different, their basic internal structure is almost the same. Because in each case the organs are composed of humerus, radius-ulna, carpal, metacarpal, and phalanges bones. The differences in the external structure of the organs occur due to their adaptation to different environments.

The forelimb of a bird has become a wing to fly in the sky, the number of fingers on the forelimb of a horse has decreased to one for fast running. The forelimb of a whale has become a flipper for swimming in the water, the forelimb of a dog is used for running. And the thumb of the human hand has moved away from the position of the other fingers in order to do fine work or to grasp an object. That is, different vertebrates originated from the same ancestor, so similarities can be seen between the homologous organs (1) & (2).

Homologous organs of plants

Like animals, plants also have homologous organs. The leaves of the cactus, the leaves of pitcher plants, the leaves of Venus flytrap, etc. are examples of homologous organs. Although they have different functions, they all belong to the same ancestor.

Such similarities between homologous organs show that organisms are interrelated. Originally they were the same. But in order to live in a different environment, some external changes or evolution of the organs have taken place. That is why scientists have speculated that organisms with homologous organs may have originated from the same ancestor. This information supports biological evolution (3).

Analogous organs

Definition

Organs of an organism that are originally or structurally different but similar in shape and function are called analogous organs. When the analogous organs of different organisms adapt in the same way to live in the same environment, it is called convergent adaptation. And this type of evolution is convergent or parallel evolution (2).

Example

The wings of bats, the wings of birds, the wings of butterflies, etc. are examples of analogous organs. Because both bats and insects use their structure are completely different. They have originated from different ancestors (4).

Analogous organs of animals

Although the wings of both insects, birds, and bats are used to fly in the sky, there are no similarities between their origin and structure. The wing of an insect is the extended part of the exoskeleton. The wings of the bird are the transformation of the forelimb. And the wings of a bat is the extended growth of skin between the forelimb and hind limb. Bird’s wings do not have carpal and metacarpal bones. On the other hand, bats have carpal and metacarpal bones. Birds have feathers on their wings and bats have hair on their wings. So these organisms, which are originally different, live in the same environment and perform the same tasks, so there is a functional similarity between them.

Another example of analogous organs is the sting of bees and crabs. Functionally, their stings are used for self-defense in both cases, but their structure is different. The bee sting is a modified ovipositor and the crab sting is a modified abdominal segment (1) & (3).

Analogous organs of plants

The tendrils of pea tree, pumpkin tree, and passionflower are examples of analogous organs of plants. Because although they are originally different, they have functional similarities to live in the same environment. The tendrils of pea trees are the transformation of leaves, the tendrils of pumpkins, and passion flowers are the transformation of stems. But since they are both weak-stemmed plants, the tendrils of both helps the tree to rise by holding on to any support. So all these plants are different in origin and structure, there are functional similarities between them. The analogous organs of plants also prove that they are evolutionarily the same.

Another example of analogous organs of plants is potato and sweet potato. Both potatoes and sweet potatoes are functionally similar. They both store food for the future. But there are differences in the origin and structure of both potatoes and sweet potatoes (3) & (4).

From the above examples, it is known that different organisms adapt equally to the same environments and as a result, functional similarities are formed between them. Analogous organs also provide evidence in support of evolution (1).

Difference between homologous vs analogous

Homologous organs and analogous organs provide important evidence in favor of biological evolution. Evidence that evolution has taken place on earth is known through these organs. These organs are different from each other. In view of the above discussion, some differences are observed between these organs. These are described below (1).

ContentHomologous organsAnalogous organs
1. OriginHomologous organs are originally the same.Analogous organs are different in origin.
2. Physical constitutionHomologous organs have similarities in the internal physical constitution.There is no similarity in the internal physical constitution of analogous organs. Their internal structure is different.
3. EnvironmentThese organs adapt to different environments.Analogous organs adapt to the same environment.
4. FunctionThere is no functional similarity between these organs.There is a functional similarity between these organs.
5. Evolution typeHomologous organs indicate divergent evolution. This is because the origin and structure of homologous organs are the same but adapted to different environments.  The analogous organs of different organisms are equally adapted to living in an environment. So analogous organs indicate convergent evolution.
6. External structureThe external structure of homologous organs is different.There are similarities between the external structures of analogous organs.
7. Cause of originHomologous organs are formed as a result of divergent adaptation.Analogous organs are formed as a result of convergent adaptation.
8. Type of creationDifferent vertebrates have similar structures and origins. So evolutionists think that homologous organisms originated from the same ancestor.The analogous organs did not originate from the same ancestor. All these organs have originated from different ancestors.
9. ExampleWings of birds, limbs of the horse, flippers of whales, limbs of dogs, human hands, The leaves of cactus, pitcher plants, Venus flytrap, etc. are the example of homologous organs.The wings of bats, the wings of birds, the wings of butterflies, the tendrils of pea tree, pumpkin tree, passionflower, etc. are examples of analogous organs (1) & (2).

Written By: Manisha Bharati

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