The comparison of the anatomy of many different species provides evidence of evolution. This morphology can be considered on the basis of the comparison of mature organism’s structure in terms of homologous, analogous and vestigial structures. However, comparative embryology can provide further evidence of evolution.
Homologous structures are structures that are common to a group of organisms that derive from a common ancestor. Homologous structures have a similar basic anatomy but may serve different functions due to the way they have evolved in different organisms over time. Homologous structures provide evidence of divergent evolution. This can be observed for example through the comparison of forelimbs of different mammals.
Analogous structures refer to structures that have evolved independently to have different functions. These structures have evolved like this due to being subjected to similar selective pressures. Analogous structures demonstrate convergent evolution. An example of an analogous structure includes a bat wing and an insect wing.
Vestigial structures are structures found in some organism that are functionless or have reduced in size due to a lack of selection pressure for their maintenance. These structures continue to remain in an organism’s anatomy despite not having a useful purpose, as there is not enough selective pressure to result in its complete removal.
Examples of these structures include the pelvis and skeleton remnants of hind limbs found in whales and snakes.
Observations of different species embryos demonstrates that certain structures that appear in modern day species embryos once existed in early ancestral species. Based on these observations it can be presumed that these modern day species evolved from a common ancestor. Examples of similarities in embryos include tails present of tails in human, pig, salamander and fowl embryos.
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