EVOLUTION

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Organic evolution is defined as the sun total of adaptive changes from old form that have taken place over a long time, resulting in diversity of forms, structures and functions among organisms.
The whole concept behind organic evolution is that all living things came into existence from preexisting living things and the various species have arisen by a gradual process of change over a very long period of time.

EVIDENCES OF EVOLUTION

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• Fossil records: A fossil is part of a plant or animal that lived a very long time (up to million of years) ago. Through the use of special techniques scientists uses what is called radio-isotope dating which are able to determine the age of fossils. By arranging the fossils according to their age, from the oldest to the most recent, they have been able to show an unmistakable evolutionary trend from very simple life forms to complex ones. Fossil record is also called geological, paleontological, archeological or historical record.

• Evidence from comparative anatomy: There are evidences of evolution in certain anatomical features of vertebrate animals. There is a progressive evolutionary change in the anatomy of the heart in all categories of vertebrates.
  Pisces have a simple heart with one auricle and one ventricle, amphibians, two auricles and one ventricle, reptiles, two auricles and a partially divided ventricles and birds and mammals have two auricles and two ventricles.. In the process of these changes, the circulation of blood also changed from a single to a double circulation.
  
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• Evidence from geographical distribution: It has been proved that living things tend to show some variations in form, functions and structures in relationship to differences in climate. In other words, no two types of the same climate produce the same type of plants and animals that have some resemblance.

• Evidence from embryology: Embryo is the organism that develops after fertilisation of the egg before birth. It is noticed that in the embryology of vertebrates, there are stages which resemble the embryo of other vertebrates from which they are believed to have evolved. For example, the embryo of man in the womb, at different stages of development resembles embryos of fish, reptiles and amphibians.
  
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• Evidence from vestigial organs: Vestigial organs are incomplete organs that have no special function. Vestigial organs are the remaining parts of once functioning organs.

• Evidence from domesticated organisms: Domesticated organisms have been used as an evidence of evolution. Which is known as specific domesticated animals like cats, hens, dogs etc. They lived with human for many millions of years. They have gone through several stages to become what they are today.

REFRENCES

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https://www.britannica.com/science/circulatory-system/The-vertebrate-circulatory-system

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1570919/

https://www.sciencedaily.com/releases/2010/12/101215112815.htm

http://www2.hawaii.edu/~pine/book1qts/embryo-compare.html

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