Biology XI Content
Evidences of Organic Evolutions
The following are the evidences of organic evolution:-
- Evidences from morphology/comparative anatomy & vestigial organs
- Evidence from embryology
- Evidence from paleontology.
- Evidence from bio-chemistry and physiology
- Evidence from Genetic.
- Evidence from geographical distribution of animals (organisms)
1. Evidence from morphology/comparative anatomy & vestigial organs
The study of morphology and anatomy of different animals suggests that their each group possesses its own pattern of organizations, but they possess some common characteristics.
It can be studied under the following sub-categories:
- Evidence from homologous organs:
The homologous organs are those having common origin and built in the same fundamental pattern but perform different functions and have different appearance. The homologous organs are found in the forms showing adaptive radiations from a common ancestor. This phenomenon is referred as divergent evolution.
For E.g. the forelimbs of frog, bird, whale, horse and human are examples of homologous organs.
- Evidence from analogous organs:
They are the organs having same functions but different basic internal structures. From the study of analogous organs, it can be clearly known that the different animals that are not closely related have developed similar adaptive features for life-in similar habitats. This phenomenon is referred to as convergent evolution.
For E.g. the wings of birds and insect are the examples of analogous organs.
- Evidences from vestigial organs:
The organs which are incompletely developed (rudimentary) and generally non-functional or without any use are called vestigial organs. During the course of evolution of new species from common ancestors, a number of organs become degenerated & non-functional. Thus, all such organs were once well and developed and functional in one or more generations, became non-functional and degenerated generation after generation.
AVATISM: Sudden reappearance of characters which was present in past generation is known as avatism. For e.g. reappearance of thick hair on the human body like monkeys, presence of short sedimentary tail in the body of new borne baby, etc
2. Evidence from embryology:
Embryology deals with the formation of embryo up to hatching or birth.
- Comparison of early stages of development:
Embryology deals with the study of changes or events leading to the fertilization and development of embryo. It is one of the most appealing sources of organic evolution. The complex organisms have the same embryo logical developmental patterns of more primitive forms. In all multicellular animals, the fertilized egg undergoes segmentation division to produce a solid structure called the morula. The morula develops into a single layered hollow blastula. The blastula then changes into either two or three layered gastrulas. The organisms with two layers are called diploblastic and those with 3 layers are called triploblastic. Such a similar early development establishes a clone relationship among all multicellular organisms.
- Comparison of Embryo of different animals:
The comparative study of embryos of some vertebrates such as fish, salamander, tortoise, bird (hen), man etc. show that they resemble one another closely. At the stage of development of embryo of different vertebrates, they resemble with each other. This shows that they are closely related in their ancestral characteristics
- RECAPITULATION THEORY:
Statement: “Ontogeny (life history) of an organism recapitulates its phylogeny (evolutionary history).” In other words, an organism repeats its ancestral history during its development.
- Development of frog:
In the development of frog, a fish like larva (tadpole) is formed, which swims with tail and respires by gills. This indicates that the frog has been evolved from a fish lie ancestor.
- Development of Hedrmania:
The tadpole larva of Hedrmania (Urochrodate) shows characters of chordates i.e. presence of notochord, well-developed dorsally placed central nervous system and tail. However, adult Hedrmania doesn’t show these characters. Thus, the larva shows its ancestral characters.
- Development of frog:
3. Evidence of Paleontology:
Paleontology deals with study of past life as revealed by fossils. Fossils are the remains of plants and animals which lived in the past ages, in the earth. It has 2 branches normally:-
- Paleozoology (study of animal fossils)
- Paleobotany ( study of plant fossils)
Leonardo da Vinci (1452-1519) is known as the father of paleontology as it is based on his observations. While George Cuvier, who established know-how modern paleontology, is known as “Founder of modern paleontology”
Paleontology is more reliable source of organic evolution because of the following reasons:
- Fossils are the remains of actual organisms which lived in past years.
- The various body parts of organisms found preserved under sea-beds, rocks, soils etc. provide the information regarding development and variation of organisms from simple to complex and developed forms.
- We can know the types of organisms found in earth at various eras by studying the age of rocks in which fossils are found in different strata.
Thus, paleontology provides a reliable source of information regarding organic evolution.
The various types of fossils are given below:-
- Entire organisms:
They are the fossils of organisms who lived about 50,000 years ago at cold, snowy parts. For E.g. in Polar
This is the type of fossils in which only hard remains of organisms get preserved while the soft parts decay.
- Cast or Mould:
The impressions which are left due to burying organisms under high pressure are called moulds or cast.
It is the plant fossils in which the outline of thin carbon film of the internal structure of plants body preserved under solid.
The foot prints of the fossils which are left behind due to the hard pressure exerted by the fact on the ground is called impressions.
4. Evidence from bio-chemistry and physiology:
The scientific study of chemistry of living organisms is known as bio-chemistry. It provides information that evolution is basi0cally biochemistry phenomenon. The physiology and biochemistry provide the following ideas on evolution:
- Protoplasm Chemistry:
Protoplasm is considered to be “physical basis of life”. The analysis of living matter in protoplasm suggests that protoplasm from sources such as bacteria, blue-green algae, plants and animals contain the same biochemical constitution (such as protein, lipids, water, carbohydrates etc). This suggests during evolution, the most fundamental property of organism remained intact while variations occurred in other constitutions.
- Chromosome Chemistry:
The chromosomes of all the living organisms consists nucleic acids i.e. DNA and RNA and protein molecules such as histone & protamines. They are arranged in identical patterns. This suggests a common origin of most living beings.
- Enzyme Similarities:
Enzymes such as trypsin, amylase, etc. are found in the digestive tracts of different organisms. These enzymes are found from sponges to mammals. Similarly, a variety of green plants bear common enzymes used in photosynthesis. Thus, it shows a common origin of organisms.
- Hormonal Similarities:
The hormones such as thyroxin are common in vertebrates like amphibians and mammalians. These hormones can be substituted from one class of organism to next. Thus, presence of hormones in vertebrates shows their common ancestry.
- Comparative Serology:
Serology deals with the study of serum (a liquid which separates out from clotting blood i.e. plasma without corpuscles & fibrinogen) of animals. During the reaction between antibody of serum and antigen (injected), a precipitate is form in organism and by studying their nature, comparison can be done. If the precipitate results with more dil. Antigen of next animals, then they are closely related otherwise they are not closely related.
5. Evidence from Genetics:
Genetics is the branch of science dealing with the study of heredity of animals and plants. There are 2 sources of genetical variations.
From many years, man has been selecting and breeding (re. hybridization) many plants and animals for their use:
- A mule, the offspring produced by the cross breading of a jack ass and a mare. It is a hybrid which is sterile and very strong. This sterility is due to the difference in number and composition of chromosome which prevents from synapsis and formation of gametes.
Thus, hybridization helps in the organic evolution.
It has a major role in organic evolution. The mutation such as gross mutation, mutation due to variation in chromosome number (polyploidy and aneuploidy) and point mutation (variation in small segment of DNA) introduce various types of plants and animals re. Helps in speciation.
Thus, mutation plays important role in evolution.