Discuss the various evidence of organic evolution
1. Comparative anatomy/taxonomy. Members of a phylum/group show similarities. Organs have similar structure. These are organs that perform the same function in different organisms such as the digestive system, urinary system, vertebrate heart.
Homologous structures are structures with the same embryonic origin but have been modified to perform different and specific functions.
This phenomenon is called adaptive radiation. Structures in organism get modified as to suit the needs of the environment. They show a form of divergent evolution. Evolution in which organisms have the same ancestral origin but occupy different ecological environments hence their body structures get modified to suit the new environment. e.g. the pentadactyl limb in vertebrates which has been modified for racing in horse; swimming horse in whale and flightwhale in bats and birds or beaks of finches and birds. Pentadactyl limb structure is based on five digits which suggest a common ancestry.
Analogous structures are those with different embryonic origin but have been modified to perform the same function due to occupation of the same environment. e.g. wings of insects, bats/birds have different embryonic origin but have become modified to carry the same function.
Another is the eyes in octopuses and humans.
Such structures show a form of convergent evolution in which the organisms had different embryonic origin but have followed the same path in modification of body structures leading to the similarities.
Vestigial structures, are those that have been reduced in size and become functionless in the course of evolution; e.g. limbs in snakes, human appendix, hair and tail.
It is suggested due to lack of need to use them, they failed to develop.
2. Cell biology/cytology. Occurrence of similar organelles such as the mitochondria and the endoplasmic reticula point to common ancestry.
3. Fossil records/Paleontology. Fossils are remains of organisms preserved in naturally-occurring materials for many years. Fossil records show morphological changes of organisms over a long period of time e.g. skull of humans and horse. They provide a direct evidence of existence of organisms at a particular ecological era. However, since only hard parts are preserved, no evidence is available for existence of soft-bodied organisms. There are many missing links since remains are accidentally preserved in rudimentary rocks and resins which do do not last for long.
Some fossils may be present in rocks but have never been found.
4. Comparative embryology. Vertebrate embryos are morphologically similar during the early stages of development suggesting that the organisms had a common ancestry/origin e.g. larvae of mollusks/annelids, embryos of chicken, humans, sheep. The closer the semblance between embryos, the closer their ancestral backgrounds.
5. Geographical distribution
Present continents are thought to have been a large land mass joined together. As a result of continental drift, isolation occurred bringing about different patterns of evolution, where plants and animals from different continents yet with common ancestry can no longer interbreed. As a result they evolved into different species. Examples of animals that moved to different areas are the jaguars and Llamas in south America, lions in Africa, Tigers in Asia, marsupials in Australia.
6. Comparative serology/physiology. Semblance in blood components such as blood proteins, antigen-antibody reactions, structure of haemoglobin in all vertebrates, reveal some phylogenic relationship among organisms or tend to show a common ancestry. Max. 20 mks
Homologous structures are structures with the same embryonic origin but have been modified to perform different and specific functions.
This phenomenon is called adaptive radiation. Structures in organism get modified as to suit the needs of the environment. They show a form of divergent evolution. Evolution in which organisms have the same ancestral origin but occupy different ecological environments hence their body structures get modified to suit the new environment. e.g. the pentadactyl limb in vertebrates which has been modified for racing in horse; swimming horse in whale and flightwhale in bats and birds or beaks of finches and birds. Pentadactyl limb structure is based on five digits which suggest a common ancestry.
Analogous structures are those with different embryonic origin but have been modified to perform the same function due to occupation of the same environment. e.g. wings of insects, bats/birds have different embryonic origin but have become modified to carry the same function.
Another is the eyes in octopuses and humans.
Such structures show a form of convergent evolution in which the organisms had different embryonic origin but have followed the same path in modification of body structures leading to the similarities.
Vestigial structures, are those that have been reduced in size and become functionless in the course of evolution; e.g. limbs in snakes, human appendix, hair and tail.
It is suggested due to lack of need to use them, they failed to develop.
2. Cell biology/cytology. Occurrence of similar organelles such as the mitochondria and the endoplasmic reticula point to common ancestry.
3. Fossil records/Paleontology. Fossils are remains of organisms preserved in naturally-occurring materials for many years. Fossil records show morphological changes of organisms over a long period of time e.g. skull of humans and horse. They provide a direct evidence of existence of organisms at a particular ecological era. However, since only hard parts are preserved, no evidence is available for existence of soft-bodied organisms. There are many missing links since remains are accidentally preserved in rudimentary rocks and resins which do do not last for long.
Some fossils may be present in rocks but have never been found.
4. Comparative embryology. Vertebrate embryos are morphologically similar during the early stages of development suggesting that the organisms had a common ancestry/origin e.g. larvae of mollusks/annelids, embryos of chicken, humans, sheep. The closer the semblance between embryos, the closer their ancestral backgrounds.
5. Geographical distribution
Present continents are thought to have been a large land mass joined together. As a result of continental drift, isolation occurred bringing about different patterns of evolution, where plants and animals from different continents yet with common ancestry can no longer interbreed. As a result they evolved into different species. Examples of animals that moved to different areas are the jaguars and Llamas in south America, lions in Africa, Tigers in Asia, marsupials in Australia.
6. Comparative serology/physiology. Semblance in blood components such as blood proteins, antigen-antibody reactions, structure of haemoglobin in all vertebrates, reveal some phylogenic relationship among organisms or tend to show a common ancestry. Max. 20 mks
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