What are HOMOLOGOUS organs?

The study of the comparative anatomy of the organs or structures of living beings evidence the relationship or kinship between species, which is why it is fundamental in the studies of biological evolution. There are organs known as homologues, analogous organs and vestigial organs. In this UnProfesor lesson we tell you What are homologous organs, their characteristics and examples!

The similar structures of various organisms can be classified according to some criteria such as origin, function and appearance. When you talk about homologous organs Two or more characteristics are considered to have a common origin.

So the characteristics are homologous between two species, When if you go back in time, that characteristic coincides with the same ancestor. Homologous organs between species are those that have a similar internal structure, but usually fulfill a different function.

Here we discover the differences between homologous and analogous organs.

Let's better understand this lesson by now discovering some

• The wing of a bird and the wing of a bat: Externally, the wings of birds and bats look very different, but if we take an x-ray to see what they look like inside, you can notice the similarity that exists between their bones. Both are forelimbs, as they develop they differentiate from an arm. In the case of birds, as they develop they resemble a wing, the bones that would be the hand fuse and others disappear. In the case of bats, the finger bones are maintained, but they are lengthened. There was another group of flying vertebrates called pterosaurs, which also had forelimbs adapted to flight. Therefore, birds, the flying mammalian bat, and the now extinct flying reptiles have homologous organs.
• Tetrapod ear bones and fish jaw bones: The ear bones of mammalian animals that have 4 limbs are the stapes, the incus and the hammer, these ossicles are homologous to certain structures of fish that are found as part of the skull: the jaw and the arches gills. Primitive fish did not have a jaw. As fish evolved, gill arches and jaws appeared. Tetrapods evolved from fish with jaws and lobe fins, the first to appear were amphibians, then reptiles and mammals. This evolutionary sequence in which certain jaw bones of fish separated until they formed part of the tetrapod ear ossicles was discovered thanks to evidence from the bones of various fossils.
• Vestigial organs: This type of organ is evident as an organ with no apparent function, like a remnant or vestige. These types of organs are usually homologous to fully functional organs in other species. Some of these organs can be evident in the embryonic stage of living beings and are lost as they develop. An example of this is the teeth in the upper jaw of whales, which later do not develop into the adult organism. Another example is the coccyx or vestigial bone of the spine of humans, it is homologous to the tail or extension of the spine of other primates.

Mammal limbs

• If we compare the limbs of a flying mammal, like the aforementioned bat, with a dolphin or whale, which are sea ​​mammals. The inside extremities, both the bat's wing and the fins of cetaceans, have the same bones and joints, only with a different size and shape. In bats the phalangeal bones are long and separated and in cetaceans they are short bones and are found more close, the function of the extremities is different in each case, in the bat they are adapted to flight and in cetaceans to the swim
• Human hand bones and pig, cow and horse limbs: In all cases, comparing with the bones of the human hand, it can be seen that there are internal structures that are maintained and others that are modified. What will differ in already developed organisms such as the pig, the cow and the horse is the number of fingers, in addition to their function and appearance. If these species are studied from their embryonic stage, it is evident that in the four cases mentioned, These have five fingers, which both the pig, the cow and the horse will lose during their life. training.

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Kardong, V. K. 2007. "Vertebrates. Comparative anatomy, function and evolution." 4th edition. Washington State University. Spanish edition. McGraw Hill Inter-American.