Homologous Structures

Homologous Structures Definition

By virtue of their similarity, homologous structures suggest that they share a common ancestor with animals and organisms. It is not necessary for these structures to look or function exactly the same. Their name hints at their structural similarity, which is the most important factor.

Examples of Homologous Structures

A Tale of Tails

Other mammals have tails, such as monkeys, cats, and rats. An extension of the torso, the tail is made up of flexible vertebrae. Cats, for instance, use their tails as a source of balance, as well as warding off insects.

Coxxyx, or tailbone, is a similar feature found in humans. The tail was once a fully-formed tail and is also thought to be an extension of the torso, consisting of rudimentary vertebrae. It does not currently serve any purpose, however, unlike the tails of other mammal species.

Considering how closely the human coccyx resembles an animal tail, scientists assume that mammals and humans share a common ancestor. Human coccyx and mammalian tail are homologous due to this link.

Eye Have a Light Bulb

There are some animals that cannot see in the same way as humans. Since deep sea creatures, like chimeras, live in such a dark environment, their eyes haven’t developed the sophisticated discrimination skills that human eyes have. It is their light receptors near the front of their skulls that provide them with visual cues, and they are unable to see color or depth.

As with light receptors, the human eye catches light and transmits it to the brain. Our eyes contain photoreceptors that allow us to perceive colors, shadows, and distance because we evolved in an environment completely illuminated by the sun. We see black-and-white and shadows through rod-shaped photoreceptors, while colors and saturation are seen by cone-shaped photoreceptors.

Evolution and environment have evolved the human eye into something far more sophisticated than deep-sea creatures, like the chimera. In spite of the fact that we see full images and the chimera only sees shadows, the fact that both eyes and light receptors “see” by taking in light confirms their potential connection to a common ancestor.

Raise Your Head High

The giraffe is a subject of wonder and amazement, and for good reason. These animals have captured the attention of all who explore the Sahara since Carl Linnaeus classified them in 1758.

The majority of attention is drawn to their long necks. In spite of their eight-foot length and 600-pound weight, they only contain seven cervical vertebrae, which are the bones of the neck. 

There are cervical vertebrae in humans as well, but they tend to be shorter than those in giraffes. Human cervical vertebrae appear shorter and squatter in comparison to those of giraffes based on the diagram of the human neck.

There are seven bones in a giraffe’s neck and seven in a human’s. Based on this number, as well as the similar spinal structure between humans and giraffes, scientists hypothesize that humans and giraffes have a common ancestor. They have structurally similar cervical vertebrae.

Related Biology Terms

  • Coccyx – The “tail bone” at the end of the spinal column of mammals. Alternatively, the coccyx may extend into a tail or may be composed of fused vertebrae.
  • A photoreceptor is a structure that detects light when it falls on it.
  • Vertebrae of the cervical spine provide support for the spine at the top.

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