Home BIOLOGY TOPIC 4: EVOLUTION | BIOLOGY FORM 4

TOPIC 4: EVOLUTION | BIOLOGY FORM 4

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TOPIC 4: EVOLUTION | BIOLOGY FORM 4

TOPIC 4: EVOLUTION | BIOLOGY FORM 4

Meaning of organic evolution

Organic evolution is a gradual change of organism from simple form to more Complex over a long period of time.

OR 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.

KEY TERMS USED IN ORGANIC EVOLUTION

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

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

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

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

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

6. 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 EVOLOTION

(i) It helps us to understand the origin of organisms especially human being

(ii) It helps us to explain how different species are genetically related.

(iii)It helps us to understand how species change over time and how they adapt to the changes.

(iv) 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.

THE ORIGIN OF LIFE

The basic idea of ‘the origin of life’ is that at one time there was no life at all on the earth, and now there is a vast range of life forms.

It is now believed that our planet Earth was formed 4 billions of years ago from the debris of a burnt-out star.

Since that time the Earth has undergone cooling and structural change giving an environment for the development of living organisms.

The first life form appeared between 3.8 and 3.5 billion years ago. Here there are least evidence for life. Earths are graphite found to be organic in billion years ago.

Photosynthesis life appeared around 2 billion years ago reading the atmosphere with Oxygen. From that time life mostly small and microscopic until about 580 million years ago when complex multicellular life erose

THEORIES OF THE ORIGIN OF LIFE

Several theories have been put to wards to explain the origin of life involve:

1. Special Creation theory.

2. Spontaneous generation theory.

3. Steady state theory.

4. Organic evolution (Chemical evolution) theory.

5. Cosmozoan theory.

1. SPECIAL CREATION THEORY

This theory states that:

“The earth and all organisms living on it were created in their present form by supernatural being called God.

This belief is found in holy books of most major religious in the world, for example, in Islamic studies, it has been stated that God created heaven and earth I six distinct phases and Adam from sounding cray, in Christianity, it is believed that God created the universe, plants, animals and Adam as the first human being in six natural days.

Strengths of the special creation theory

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

ii. The existence and different ages of fossils prove that living appeared on earth in different times frames.

Weaknesses of the special creation theory

i. It was based on religious belief or faith.

ii. There is no scientific evidence to support the theory since it is based on faith.

2. SPONTANEOUS GENERATION THEORY

This theory states that:

“Living things arose from non-living materials on a number of distinct occasions.

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.

This theory is also known as abiogenesis

ABIOGENESIS

Is the concept of living things arising from non – living matters Or 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 are needed.

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. Examples active principles include fertilized eggs, seeds, sunlight, wheat, decaying meat and mud. There are several observations supporting this history. For example, fly larvae (maggots) tend to develop on 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 the spontaneous generation theory

i. It offers the mechanisms to argue on how life arose on the earth.

ii. The theory can be proved by scientific experiments and research.

Weaknesses of the spontaneous generation theory

The theory violates the law of biogenesis which show that life arises from pre – existing life.

3. 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 theory does not clearly explain the mechanisms through which life was brought to earth.

ii. The theory does not state where life originated and therefore it can not be called the theory of origin of life.

iii. There is no scientific experiment to support the cosmozoan theory.

4. STEADY STATE THEORY

This theory states that:

“Life had no origin and it has always 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 they become extinct.

Strengths of the cosmozoan theory

It is true that the earth support life and it undergoes slight changes.

Weaknesses of the cosmozoan theory

i. The assumption that life have no origin 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.

Biogenesis is a concept which indicates that life arises from pre – existing life

5. CHEMICAL EVOLUTION THEORY

This theory states that:

“Life on the earth resulted from chemical reaction of molecules.”

Or “Life arose on the earth because of physical and chemical reactions of naturally occurring elements and molecules.

These molecules gradually accumulated in the oceans and formed a hot primordial soup. The cooling of the primordial earth favoured reactions among the gaseous molecules such as carbon, hydrogen, nitrogen, and oxygen. The reactions led to the formation of simple organic compounds such as amino acids, nucleic acid, sugars.

The nucleotides and nucleic acid that 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.

QUESTIONS

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.

ORGANIC EVOLUTION

Organic evolution is characterized by a gradual change of organisms from primitive to advanced forms.

Through organic evolution it can be stated that the recent types of plants and animals originated from pre – existing forms called ancestors.

The existing difference between ancestors and modern descendants are due to modifications over many generations.

THEORIES OF ORGANIC EVOLUTION

These theories attempt to explain the mechanism by which organic evolution operates (how new life forms emerged (arose) from pre-existing ones). The following are some theories of organic evolution

1. Lamarck’s theory of evolution.

2. Darwin’s theory of evolution.

1. LAMARCK’S THEORY OF EVOLUTION (LAMARCKISM)

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 an organism’s organ

ii. Inheritance of acquired characteristics

iii. Needs of the environment

(i) NEED (DEMAND)

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

(ii) THE USE AND DISUSE

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

(iii) INHERITANCE OF ACQUIRED CHARACTER

Lamarck proposed that changes or characteristics acquired during the lifetime of an individual can be transmitted to the offspring.

Or

Physical changes in an organisms acquired during their lifetime, such as development of an organ or a part through increased use or disuse could be transmitted to their offspring.

LAMARCK’S OBSERVATIONS

Lamarck supported his ideas on evolution by the following observations:

i. Development of long neck giraffe

ii. Development of webbed feet on ducks

iii. Development of flightless birds

(i) DEVELOPMENT OF LONG NECKED GIRAFFE

Lamarck proposed that the ancestral giraffes had short necks and fore legs. They lived 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 longer 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 modern giraffe emerged.

Figure 1: Evolution of long necked and legged giraffes

(ii) DEVELOPMENTS OF WEBBED FEET ON DUCKS

According to Lamarck the present day webbed duck was originally not webbed. Due to the lack of food on the land they were forced into water looking for food and because of constant spreading of their toes during swimming the skin between the toes stretched and grew into webs. Then this acquired character (webbed feet) got inherited from one generation to another generation.

Ancestral duck Modern duck

(Unwebbed feet of the duck) (Webbed feet of the duck)

(iii) DEVELOPMENT OF FLIGHTLESS BIRDS

Lamarck proposed that flightless birds such as ostrich, kiwi, penguins and emu lived on environment with no requirement of flight hence their wings reduced and became functionless.

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.

2. DWARN’S THEORY OF ORGANIC EVOLUTION(DWARWINISM)

Charles Robert Darwin was an English naturalist. He was the first person to explain evolution scientifically.

He made a five years journey (geographical study) in various parts of the world.

During his five years journey he collected different species of plants and animals and he developed the theory of organic evolution based on the concept of natural selection

NATURAL SELECTION

Is a mechanism by which organisms that are better adapted to their environment survive and reproduce, while the less adapted fail to survive.

Species tend to change from generation to generations as they do so, they adapt to a new environment.

MAIN IDEAS OF DARWIN’S THEORY OF EVOLUTION

Darwin’s theory is based on the following observation and deduction

i. Overproduction of offspring

ii. Population of each natural species remain more or less constant in number

iii. Members of the same species show variation in characteristics.

iv. Some characteristics are inherited and passed on the next generation.

(i) Overproduction of offspring

Darwin observed that all living things are capable of producing more offspring than the environment can support. For example, sea turtles can lay from 70 to 190 eggs at a time, oysters can lay between 60 and 80 million eggs at a time.

(ii) Population of each natural species remain more or less constant in number
Despite the high rate of reproduction among the members of the species, the number of individuals remain fairly constant over long periods of time in many species.

From these observations Darwin reached the following deduction (conclusion):

There is struggle for existence

Darwin concluded that overproduction results in competition among newly produced organisms due to limited resources including food, shelter, space and mate. Many organisms either fail to reproduce or die before reaching the reproductive age.

Natural selection or survival of the fittest

In the struggle for existence, only those organisms with favourable adaptive characteristics have reproductive and survival advantages. Those with unfavourable characteristics have limited chances in the struggle for existence and therefore perish.

Darwin concluded that, nature selects only those organisms which carry favourable characteristics. Organisms selected naturally are better adapted to their environment and transmit their survival traits to their offspring

Inherited features

The characteristics that favour an organism to survive in a particular environment are selected in a natural way. For natural selection to act on a certain characteristic there must be variations. The variations have to heritable.

STRUGGLE FOR EXISTENCE

Are the all effort that an organism performs in order to stay alive for example competing for food, shelter, space and mate.

OR

This means that organism that live in a limited resources environment tend to compete for the resources in order to survive.

(iii) Members of the same species show variation in characteristics

Members of the same species show variation in characteristics such as colour, shape, size or behaviour

(iv) Every generation of organisms have more off springs than parents.
However, the numbers of adult organism remain generally stable (constant) from generation to generation.

Therefore, it is struggle for existence that causes many off spring to die before becoming adults.

There are many variations in a species.

Variations are passed from parents to their offspring.

Advantages of variations enable survival in the environment. Organisms with disadvantageous variation die. This is called Survival for the fittest.

Offspring with favourable variations grow into adults and reproduce.

SURVIVAL FOR THE FITTEST

This mean that when organism compete for the limited resources during struggle for existence, the organisms that are well adapted (strong), survive to adulthood unlike less adapted (weak) organisms tend to die.

OR

This means that during struggle for existence the organism with favourable characteristics survive to reproductive maturity and while less adapted are eliminated.

OR

-This means that in struggle for existence only fittest organisms survive while less adapted are eliminated.

OR

This means that in struggle for existence only fittest organisms survive while less adapted are eliminated.

NATURAL SELECTION

Is a process whereby nature selects the organisms that have favourable characteristics to be parents of the next generation while weeding out those lack favourable characteristics.

DEVELOPMENT OF LONG NECKED GIRAFFE ACCORDING TO DARWIN.

According to Darwin both forms of giraffe (Long and short necked giraffe) existed but according

to the shortage of food on land, giraffe were forced to feed on the tall trees (struggle for existence)

From this, long necked giraffes were on advantageous side as they were unable to reach the leaves of tall trees.

Therefore, the long necked giraffes won the struggle for existence (competition) and those which survived they passed their long necked character to their offspring.

The short necked giraffes failed in the struggle for existence and therefore natural selection selected them negatively i.e. they died.

STRENGTHS/MERITS OF DARWIN’S THEORY

i. It enabled scientists to carry on with further studies on environment.

ii. It explains evolution more scientifically.

iii. It put more emphasize on the role of the environment in evolution.

iv. It led to the discovery of genetics.

WEAKNESS/SHORTCOMING OF DARWINS THEORY

i. It points out that natural selection favor the fits and eliminate the units, but it does mot indicate clearly how the fits are cleared and maintained.

ii. It does not explain how characters are inherited from one generation to another and hence does not consider the role of genetics in evolution.

iii. It failed to distinguish between inheritable and non-inheritable traits/characters.

iv. Mutation and gene interact as agents of evolution are not considered by the theory.

FACTORS THAT BRING ABOUT EVOLUTION.

1. Mutation.

This is the sudden (rapid) genetic change which may involve individual genes, chromosomes, or sets of chromosomes.

The mutant is the organism which mutation set up always appears different from the rest of the population.

2. Migration

Immigration and emigration affect the size of the population and also alter the gene frequency.

3. Environmental change (Physical barrier)

Some environmental factors affect individual in a population in such a way that they do not pass their characteristics to he next generation.

The environmental changes Include Isolation by physical barrier such as oceans, mountains and deserts.

4. Crossing over.

Exchange of genetic material result to an organism with combined character which differ from that of parent hence result to evolution.

5. Artificial selection.

This involves examining an organism and selecting the desired characteristics.

It ensures storage of good character while poor traits are lost.

Both inbreeding and out breeding favour good (desirable) characters hence pass the genes from generation to generation.

APPLICATION OF ORGANIC EVOLUTION IN THE REAL LIFE SITUATION
(NATURAL SELECTION IN ACTION)

Natural selection that results in the formation of new species occur within long time. Therefore for this reason body has even observed it happening however it is now possible to demonstrate evolution in a small scale(Micro evolution)

1. Sickle cell Anaemia.

Is the hereditary disorder in which the red blood cells make a sickle shape. -People with sickle cell anaemia are more resistance to malaria since malaria is important cause of death in this area people with sickle cell are selected for (favourable) survive while normal people die (eliminated)

2. Resistance to drugs, Insecticides and antibiotics.

In recent areas many organisms has developed resistance against insecticides and drugs that were formerly used to kill them. When the drugs firstly killed many of them but some of them (few) survived these organisms which survived had beneficial trait which later they reproduce offspring that are able to resist against drugs.

For example: Bacteria are resistant to Anti TB, Flies are resistant to DDT.

Through that organism that were able to resist were favoured while unable were eliminated (died) hence we call natural solution.

3. Melanin pigment

In British before Industrial revolution there were two types of moth which were Dark

Melanin Moth and White (Lighter) speckled Moth, before the Industrial revolution White speckled Moth were common in tree trunk where they protected themselves against enemy like birds since they were not seen easily like how dark melanin Moth hence they were in advantageous side than dark moth.

But after Industrial revolution, the smoke and soot darkened the tree trunks and branches. As the result the melanin dark forms of moth were almost invisible against the dark background of the darkened tree trunks and branches making them less subjected to predation.

Predators easily spotted the speckled white forms and hence their number decreased.

EVIDENCES OF ORGANIC EVOLUTION

These refer to the things that show that either evolution occurs or occurred in the past time i.e. through the following are the important sources of evolution evidence.

1. Fossil records.

2. Cell biology.

3. Comparative physiology.

4. Comparative embryology.

5. Comparative anatomy.

6. Continental draft.

1. FOSSIL RECORDS.

Fossils – Are remains of organisms that lived in ancient times.

The study of fossils is known as PALEONTOLOGY.

Fossil record indicate that organism have evolved from simple life form to the complex life form, as most of the fossils of the organism that died few years ago show in comparative to the ancient fossils.

Example the fossils of human beings indicates that human being evolved from primates.

2. CELL BIOLOGY

Genetic analysis reveals that the diverse organisms are related.

All cells of higher organisms show basic similarities in their structure and function. For example, the presence of cell membrane, mitochondria and ribosomes which perform similar functions in all cells proves that they evolved from the same ancestor. -Also, all cells have DNA as the carrier of genetic information and use ATP as energy carrier.

-Therefore, these similarities in cells structures and function among different organism show that they have a common ancestor but became different because evolution occurred upon them.

3. COMPERATIVE EMBRYOLOGY.

EMBRYOLOGY– is the study of embryos.

The studies show that embryos of Vertebrates i.e. fish, birds, Amphibians, reptiles and mammals show resemblance during the early stage of development.

For example, all vertebrates’ embryos develop tails and gill slits.

This resemblance suggests a common ancestor.

4. COMPERATIVE PHYSIYOLOGY.

PHYSIOLOGY: Is the study of body function.

Many physiological processes are similar in different organisms. For example all organisms undergo respiration. This similarity in physiological processes among different organisms show that the organisms originated from the same ancestor but became different just because of evolution.

5. COMPERATIVE ANATOMY.

ANATOMY: Is the study of biological structures in different organisms.
Organisms with basic structural similarities are said to have a common ancestor but organisms whose their structures show much difference have less evolutionary relationship.

Through comparative anatomy the following structures are seen.

i. Homologous structures.

These are structures with the same ancestral origin but perform different functions. -E.g. Beaks of birds, limb structures in vertebrates and feet structures in birds.

This type of evolution is called divergent evolution.

Divergent Evolution: is a type of evolution whereby organisms with similar ancestral origin develop structures that perform different functions.

This occurs when organism become adapted to different habitat (environment and life style)

ii. Analogous structure.

These are structure with different ancestral origin but perform the similar functions.

E.g. wings in both birds and Insects, Eyes of human being and Octopus.

This type of evolution is called convergent evolution.

Convergent evolution: is a type of evolution whereby organisms with a different ancestral origin develop structures which appear similar in form and function.

This is brought about by adaptation of unrelated species to similar environment.

iii. Vestigial structures.

Are structures which have been greatly reduced and ceased to be functional. The presence of vestigial organs is an indication that they existed in ancestral forms but as a result of evolution such structures have been so much reduced to the extent of losing or greatly changing their original function.

Examples of vestigial structures.

> Wings of flightless birds i.e. Ostriches

> Appendix in man

> Coccyx (tail) in man.

> Hind limbs in python and whale.

6. CONTINENTAL DRIFT.

It is believed that, the present continents were once a large single landmass. This landmass broke up into parts which drifted away from each other.

Due to the drifting of the various continents organisms with a common ancestral origin became isolated and hence evolved into different species.

236 COMMENTS

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