The homologous organs are those having the same or similar internal structure, but may be adapted to very different functions. Their resemblance confirms that they come from a common ancestor.
For example, the forelimbs of vertebrates, such as the human arm, the fin of a dolphin, or the wing of a bird are homologous organs, with similar structure, but different functions. They would have a common ancestor, but by divergent evolution, organisms adapted to the environment in which they lived.
The similar bodies are those having a different structure but having a similar shape and function. They are evolutionarily very separate species, but they have adapted to the same environment, which is why they have developed analogous organs that have been successful in that environment.
For example, the wings of a fly and those of a bird are analogous organs. Both wings are used to fly, although they do not have a high degree of kinship. They are similar because the two have evolved adapting to flight. In this case, convergent evolution occurs and living beings repeat the designs that have been successful.
The vestigial organs are present in living but not used. They are atrophied, non-functional organs, but they were functional in their ancestors. The original function of that organ has been lost with evolution.
Humans have some of these vestigial organs, such as the appendix, the coccyx (coccyx, the rest of the missing tail), the wisdom teeth, the plica semilunaris (rest of the nictitating membrane or third eyelid of other animals), the meat chicken (to lift the hair and appear larger to intimidate enemies), or the nipple in men.
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