Organic Evolution

Organic evolution

Many evidences show that the first organisms had a single cell and it was originated in water. Organic evolution is the process of gradual and orderly changes in organisms from one form to another.

Evidence of evolution

• Evidence from fossils or paleontological evidence
• Evidence from comparative morphology and anatomy
• Homologous and analogous organs
• Vestigial organs
• Evidence from embryo or embryological evidence
• Evidence from connecting animals

Evidence from fossils or paleontological evidence

Traces and preserved remnants of dead animals and plants are called fossils. The study of fossils is called paleontology. Age of the fossil can be determined by techniques like carbon-dating, uranium-dating etc. Paleontological studies reveal following things:

• There were some organisms in the past. They are extinct now.
• The organisms which existed in the past were different from the present day forms.
• Some animals and plants were most abundant in one period, but later on, they disappeared.
• The organism that existed in the past linked one group of organisms to another group.
• It shows gradual progress from simple to complex forms through geological time scale.

Evidence from comparative morphology and anatomy:

Each group of animals and plants has its own pattern of body organization and it possesses a common set of characteristics. Generally, the term morphology is related to the study of form (external structure) of organisms and anatomy is specially related to the study of internal structures.

Evidence from morphology and anatomy can be studied in following two steps:

• Homologous and analogous organs

  

  Homologous organs are those organs which have a similar embryonic origin and basic plan but different function. The forelimbs of whale, horse, man, bat and bird are homologous organs.

  When the wings of a bird or bat are compared with the wings of an insect, it is found that they have similar functions but different in basic plans, such organs are analogous organs.

• Vestigial organs

  Those organs which are present as reduced structures and are functionless in the body are called vestigial organs.

  Evidence from embryo or embryological evidence

  An embryo is defined as a multicellular structure that is developed from the zygote and gives rise to new offspring generally present inside the female tissue or egg-membrane. A branch of biology that deals with the study of formation and development of the embryo is called embryology.

Evidence from geographical distribution of organisms

Darwin, an English naturalist, visited the Cape Verde Island which lies near the coast of Africa, during his voyage on the beagle. The organisms found on these islands resembled closely to those found on the nearby shore of Africa. Many geographical Structures like oceans, rivers, mountains etc. isolate animals and plants. When organisms grow in new habitats or in a different climate, some changes take place in them which lead to evolution. In this way, geographical distribution of organisms also gives the evidence of evolution.

Evidence from connecting animals

Some animals stand between two groups of animals and have the characters of both groups. These are called connecting links or bridge animals. Propoterus is a lungfish which possesses fish-like characters as well as amphibian-like characters. Archaeopteryx is a connecting link between reptile and birds.