Notes, Exercises, Videos, Tests and Things to Remember on Organic Evolution
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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 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:
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 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.
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.
The study of fossils gives the following information supporting the evolution:
a) The organisms existed in the past were different from the present day.
b) Some animals like dinosaurs were existed in the past which had been already extinct.
c) The study of fossils shows the gradual and continuous progress of organisms from simpler to the complex forms.
d) It also shows that new types of species appeared in one period and become abundant in the next period and gradually disappeared in the later periods.
Archaeopteryx has both the characters of reptiles and birds as follows. So it is known as the connecting link between the reptiles and birds.
|Reptilian characters||Bird like character|
|Presence of teeth, claws in wings scales on the body and tai vertebrate.||Presence of wings, beak and body covered with fur.|
The vermiform appendix in the human body is a functionless and reduced organ which is in the well-developed form in the herbivores. So, it is called vestigial organ.
Homologous organs are the organs in the different organisms which have the same basic structures and origin but different functions like forelimb of human, wings of bird, forelimbs of horses etc. The same basic structure of these organs shows that the birds, man and horses were evolved from the common ancestors and hence, this supports evolution.
In human body vestigial organs like vermiform appendix are functionless. In rabbit, goat, it is functioning for digestion but in carnivores, like tiger, it is absent. It shows that there is evolution. Thus study of vestigial organs helps to prove evolution.
Platypus is oviparous and has beak like in birds; has fur and mammary glands like in mammals. So, platypus is considered as a bridge animal between birds and mammals.
Dinosaurs get extinct in Mesozoic era, because they were too large to hibernate in dens and they had no fur or feathers to be protected from the extreme cold. In this era the earth's climate was too cold. Similarly, they could not compete with mammals for their existence.
The differences between vestigial and homologous organ are as follows:
|Vestigial organ||Homologous organ|
|In many plants and animals, there are several rudimentary functionless organs. These organs are called vestigial organ.||The organ which are similar in structure but differ in functions are called homologous organs. E.g. leg of horses, wings of bat, etc.|
Nature selects the suitable species to allow them to survive. At the time of natural selection, only these organisms survive which have favorable or suitable variation and others die. So, it is also known as survival of the fittest.
i) Embryological Evidences:
If we compare the embryos of different groups of animals, they resemble with one another in their stages so much that is really difficult to identify them. While the embryos develop gradually, they began to differ from one another. For example, the embryos of fish, tortoise, hen, pig and human beings resemble much with each other. The evidence also makes clear that the evolution takes place gradually from simple to complex form.
ii) Evidence from vestigial organs:
Those organs which are present as reduced structures and are functionless in the body are called vestigial organ.
A number of vestigial organs are found in different organisms. Halters of flies, right lung of snakes, vermiform appendix, nictitating membrane, muscles of external ears, hairs on body, canine teeth, tail vertebrae, etc. in human are examples of such organs. These organs are well developed in lower forms but in higher animals they are in extinction condition. Thus, it proves evolution.
Traces and preserved remnants of dead animals and plants are called ______.
none of the above
The many objections raised against evolution can be characterized as ______.
without scientific merit
The similarity of bone structure in the forelimbs of many vertebrates is an example of ______.