Question

define homologous and vestigial structures and their evolutionary significance

Answer 1

In biology, homology is similarity due to shared ancestry between a pair of structures or genes in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales and the forelegs of four-legged vertebrates like dogs and crocodiles are all derived from the same ancestral tetrapod structure. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.

Following are some examples of homology: The arm of a human, the wing of a bird or a bat, the leg of a dog and the flipper of a dolphin or whale are homologous structures. They are different and have a different purpose, but they are similar and share common traits.

Homologous structures are structures that are similar in related organisms because they were inherited from a common ancestor. These structures may or may not have the same function in the descendants below They all have the same basic pattern of bones. They inherited this pattern from a common ancestor. However, their forelimbs now have different functions.

Vestigial structures

A "vestigial structure" or "vestigial organ" is an anatomical feature or behavior that no longer seems to have a purpose in the current form of an organism of the given species. Often, these vestigial structures were organs that performed some important functions in the organism at one point in the past.

Structures that have no apparent function and appear to be residual parts from a past ancestor are called vestigial structures. Examples of vestigial structures include the human appendix, the pelvic bone of a snake, and the wings of flightless birds.

Vestigial Structures

Structures like the human tail bone and whale pelvis are called vestigial structures. Evolution has reduced their size because the structures are no longer used. The human appendix is another example of a vestigial structure. It is a tiny remnant of a once-larger organ. In a distant ancestor, it was needed to digest food. It serves no purpose in humans today.

An example would be the wings of pterodactyls, birds, and bats. They have a somewhat similar structure, but each of these things evolved the trait of wings entirely separately.

So, the significance of homology to the study of evolution is that it implies macroevolutionary change over time. If several related species have a trait that is more or less the same exact trait (modified a bit because of natural selection), then it must be the case that one species can diverge into two distinct species. Without macroevolution, all similar traits across different species would be, at best, analogy.