WhatsApp Channel Join Now
Telegram Group Join Now

4. 0 Evolution- Form four topic biology



4.1. Concept of organic evolution 
4.2. Theories of origin of life,
4.3. Theories of organic evolution 
4.3.1. Lamarckism
4.3.2. Darwinism 
4.4. Evidence of organic evolution 
4.5. Concept of organic evolution 

 Organic evolution is gradual changes and development of organisms from simple life forms to more complex life forms over the course of time. 


Organic evolution is the gradual change in heritable characteristics of biological population over a successive generation. 

Evolution is marked by emergence of new species from pre-existing species and the disappearance of some species.  

The species that disappear are said to become extinct

Therefore, Organic evolution is the process of change by which new species are formed from preexisting one.

Key terms used in organic evolution

Carbon dating: Is a method of estimating the ages of dead materials of biological origin. 

Natural Selection: Is selective force occurring in nature, which is responsible for eliminating the unfavorable traits to retain only favorable traits in the population. 


is the mechanism of environment itself to select organisms to be able to survive on it

Species: Are organisms, which have ability to interbreed freely to produce fertile off springs. 

Fossils: Are the remains of organisms that lived in the past, preserved naturally in rocks, peat or ice. 

Speciation: Is the emergence of new species from the pre-existing one. For example, the emergency of man from gorilla (chimpanzee). 

Extinction: Is the dying out or termination of one or several species. 

Causes of extinction

Failure of an organism to adapt to the environmental changes. 

Destruction of habitats such as deforestation 

Natural calamities such as floods, wildfires, earthquakes and drought. 

Advantages of extinction 

It opens up opportunities for new species to emerge

Importance of studying organic evolution  

1. To understand the origin of organisms especially human being 

2. Evolution and its associated theories help to explain how different species are genetically related.

3. It helps us to understand how species change over time and how they adapt to the changes of the environment 

4. It helps us to solve biological problems that impact human lives. For example, researchers study the evolutionary history of disease – causing genes in order to control hereditary diseases. 

5. Organic evolution helps us to know forces of organic evolution 


a) Give the meaning of the following terms 

  I. organic evolution 

  II. Carbon dating

 III. Fossil

b) Explain five importance of studying organic evolution 

 4.2 Theories of the origin of life  


a) Outline basic ideas of about origin of life 

b) State the theories of origin life 

c) Explain merits and demerits of each theory of origin of life 

Theories of the origin of life

There are different explanations on how life originated on the earth Origin of life is the most controversial topic in Biology. There are several theories that explain the possible mechanisms by which life originated.

There are about five theories that try to explain the origin of life on earth. These theories are:

1. Special creation theory

2. Spontaneous generation theory

3. Steady state theory

4. Cosmozoan theory

5. Organic evolution theory.

1. Special creation theory

This theory states that, the earth and all organisms living on it were created by supernatural power called God.

This is the most widespread and popular theory. This belief is found in holy books of most major religions in the world.

For example, in Islamic studies, it has been stated that God created heaven and the earth in six distinct phases and Adam from a sounding clay. In Christianity, it is believed that God created the universe, plants, animals and Adam as the first human beings in six natural days.

 Strengths of the special creation theory

1. It opened up the minds of scientists to speculate on the origin of life on the earth. 

2. It is true that life is supported on the earth 

3. The theory is purely based on religious belief or faith

Weaknesses of the special creation theory

1. There is no scientific evidence to support the theory since it is based on faith. (Theory cannot be proved scientifically)

2. The existence and different ages of fossils prove that living organisms appeared on earth in different time frames (phases).

2. Spontaneous generation theory

This theory states that: “Living things arose from non-living matter’’. This theory is also known as abiogenesis.  

Abiogenesis is the hypothetical process in which life is generated from non-life. This happens when there are favourable conditions and that no causal agent such as parents. 

This was explained by the Greek philosopher Aristotle who believed that certain particles of matter contained active principles which could produce living organisms under favourable conditions. 

The scientists believed that simple organisms like worms and frogs could arise from mud, dust or rotten food. Also, they believed that maggots arise from rotten meat.  

Ancient Egyptians believed that rats arose from the mud of ricer Nile. And amount Greeks believed that rats arose from Garbage. The theory was finally disapproved by laws Steven 1860-1895 who showed that even Microorganisms arose from previously existing ones.

Strengths of spontaneous theory

1. The theory is scientific since it can be proved by scientific experiments and research.

2. It provides mechanisms on how life arose on the earth. 

Weaknesses of spontaneous theory

1. It is not true that life arise from non-living matter. Life arises from preexisting life. Louis Pasteur made such a disapprove. Life cannot arise from non-living matter, but life arise from preexisting organism theory violates the law of biogenesis which show that life arises from

Life cannot arise from non-living matter, but life arise from pre-existing organism this theory violates the law of BIOGENESIS which show that life arises from pre – existing life

Lamacksim theory weakness

3. Steady state theory

This theory states that: “Life has no origin, and it has been supported on the earth” 

According to this theory the earth has no origin. It has always been able to support life and it has undergone very small changes. 

The living organisms had no origin, the only change their members by increasing or decreasing or become extinct.

Strengths of steady state theory

1. It is true that the earth supports life, and it undergoes slight changes.

2. This theory open mind of scientist to explain and speculate more about origin of life. 

weaknesses of steady state theory

1. assumption that life have no origin is against the law of Biogenesis which indicates that life arises from pre-existing life. 

2. The theory does not give explanation on the origin of the life, cannot answer the question of where life existed before the formation of Earth.

3. If species had no origin, then the origin of life on earth cannot be tested experimentally

4. Cosmozoan theory

This theory states that: “Life on the earth originated from somewhere else” 

 Example the existence of UFO’s that appears at a particular time disappears without actual knowing where the habitat. 

Strengths of the cosmozoan theory  

(i) Life is truly supported on earth. 

(ii) The theory is supported from the fact that fossils of microorganisms were found by scientists in meteorites in 1961. 

Weaknesses of the cosmozoan theory 

(i) The assumption that life have no or igin is against the law of biogenesis which indicates that life arises from pre – existing life. 

(ii) The theory cannot answer the question of where life existed before the formation of earth. 

(iii)If species had no origin, then the origin of life on the earth cannot be tested experimentally

5. Biochemical OR organic evolution theory

The theory states that life arose on Earth because of physical and chemical reactions of naturally occurring elements and molecules to form complex organic molecules which develop into  living organisms.

Natural occurring gaseous molecules such as carbon, hydrogen, nitrogen, and oxygen reacted led to the formation of simple organic compounds such as amino acids, nucleic acid, sugars. 

The nucleotides and nucleic acid are the main components of all living cells marked the beginning of life. 

There simple chemical compounds gradually reacted to form large complex organic molecules such as protein, polysaccharides and nucleic acid which are the most common molecules of living things hence it is believed that the first simple cell of organic molecule. 

Strengths of chemical reaction theory 

(i) It can be tested experimentally 

(ii) The theory also recognizes the role of amino acids and proteins in forming the basis of life. 

(iii)The theory encourages critical thinking and thus enhances the development of inquisitive mind. 

Weaknesses of chemical reaction theory 

(i) The theory failed to provide a viable mechanism to generate a primordial soup. 

(ii) Its unguided chemical processes cannot explain the origin of genetic code. 

(iii)The theory also fails to explain the transition from complex organic molecules to living organisms. 


1. Explain the main ideas in the special creation theory of the origin of life. 

2. Differentiate between spontaneous generation theory and steady state theory 

3. Describe two strengths and two weaknesses of the cosmozoan theory. 

4. What are the major arguments of the cosmozoan theory on the origin of life? 

5. Outline the main ideas in the biochemical theory of origin of life. 

4.2 Theories of organic evolution  

There are various theories that explain the mechanism by which organic evolution operates. Some of these theories include      

1. Lamarck’s theory of evolution. 

2. Darwin’s theory of evolution

1. Lamarck’s theory of evolution (lamarckism) 

Lamarck was the first scientist to explain the organic evolution 

Jean Baptiste Lamarck was a French naturalist. He formulated a theory of evolution after studying botany and the fossils of marine invertebrates. 

The theory suggested that individuals adapt to their environment then pass on the traits they acquire to their offspring (inheritance of acquired characteristics)”.  

The main ideas of lamarck’s theory  

Lamarck’s theory of evolution based on the following ideas: 

(i) The use and disuse of the body parts  

(ii) Inheritance of acquired characteristics 

(iii) Needs of the environment  

(i) Need (demand) of the environment  

Lamarck proposed that an organism developed a particular structure in response to demand/need of the environment. 

(ii) The use and disuse of the body parts 

Lamarck proposed that when the body part is constantly used becomes stronger and more efficient but if the body part is less or not used, it becomes weak or disappear. 

(iii) Inheritance of acquired character 

Lamarck proposed that the modification or changes that organism acquire during their lifetime are passed/ transmitted to the offspring.  


Physical changes or characteristics acquired by an organism during their lifetime are automatically handled down or passed from one generation to another .  

Lamarck’s observations 

Lamarck supported his ideas of Inheritance of acquired characteristics on evolution by the following observations: 

(i) Development of long neck giraffe 

(ii) Development of webbed feet on ducks 

(i) Development of long necked giraffe 

Lamarck proposed that the ancestral giraffes had short necks and fore legs and They were living in plains and fed on grasses. When the environmental conditions changed, grasses became unavailable. This forced the giraffe to feed on the leaves of tall trees. For giraffes to reach the leaves, they had to stretch their neck muscles and fore legs. Continuous stretching of the fore legs and neck muscles resulted in long neck and fore legs as seen in modern day giraffe. These acquired new characteristics (long neck and fore legs) were inherited from one generation to another until the now all giraffes have long neck and leg 



(ii) Developments of webbed feet on ducks 

According to Lamarck, He proposed that the present-day webbed duck was originally not webbed. Due to the lack of food on the land they were forced to move into water looking for food in water they faced problem of sinking during swimming they developed skin between the toes (digits) which developed into webs. Then this acquired character (webbed feet) become inherited from one generation to another generation. 



Strengths / merits of lamarck’s theory 

(i) It opened a way for scientists to work on the cause of evolution. 

(ii) It realizes the role played by environment on the cause of evolution.

(iii) It is true that constant use of the body part (Organ strengthened)

(iv) It led to the further studies on evolution of species. 


Limitations / weaknesses/ demerits of lamarck’s theory 

(i) It is not true that, the use or disuse of the body parts determine their existence or disappearance. 

(ii) It does not explain how characteristics are inherited from one generation to another. 

(iii) The theory cannot be proven experimentally  

(iv) Organisms do not form new organs simply by their wish or requirement.  

(v) Lamarck did not have knowledge of genetics. 


1. Describe the main ideas of Lamarck’s theory and give at least 2 examples used to support the theory by his thoughts.  

2. State the merits and demerits of Lamarckism


Next Post Previous Post
No Comment
Add Comment
comment url