1. Morphological variations

2. Physiological variation

3. Application of variation




Evolution is the cumulative changes in the characteristics of population or organisms occurring in the course of successive generations related by descent. Variations are differences in traits or characteristics between individuals of the same species. Morphological variation is change in the form and structure of an organism, while physiological variations are changes in the body functions or behavior of a population. Both types of variation can contribute to adaptation, or the ability to survive and reproduce in a particular environment.

Morphological variations occur at many different levels, including differences in size, shape, color, or other physical characteristics. These variations can be caused by environmental factors, such as diet and climate, or genetic mutations and sexual selection. For example, animals living in a cold environment may have adapted to become larger in order to maintain body heat, while those living in warmer climates could have developed smaller bodies for the same purpose. Physiological variations also play an important role in evolution, as changes in metabolic pathways or hormone levels may alter the way organisms respond to their environment and interact with other species.

Although variation is a natural process that occurs over long periods of time, human activities can also impact evolution by introducing new mutations into the gene pool or by changing ecosystems.

Variation can be:


I.                  Discontinuous or


II.               Continuous.


I. In Discontinuous variation, individuals fall into distinct categories e.g. Pea plant with either red flowers or white flowers. There are no intermediate forms between these traits. They are easily distinguishable and are not affected by environmental conditions. Variation in this category is caused by changes in the genes


Examples of such traits are


i.                   The ability to roll the tongue


ii.                 Taste phenylthiocarbamide (PTB),


iii.               ABO blood groups in man and


iv.               Normal and vestigial wings in Drosophila.


Such discontinuous variation is brought about by one or a few genes.


II.  In Continuous variation, there is a complete range of measurements from one extreme to another. In other words individuals do not fall into discrete categories,


Examples includes:


i.                   The colour of skin


ii.                 Height etc

II. Continuous variation describes traits that can take on any value within a range, such as height or skin color, and are usually controlled by multiple genes. Environmental factors may also play a role in determining how these traits develop over time. For example, variations in rainfall may affect coloration patterns of certain animals living in desert environments.


Man is not just dark or fair, nor is he either tall or short. There are many intermediate skin colours and heights. Such characteristics show a continuous variation from one extreme to the other. A continuous variation is brought about by the combined (or additive) effects of many genes.


There may be genes for dark skin and gene for fair skin. The more dark-skin genes a person has, the darker will his skin colour be. Continuous variations are also affected by the environmental conditions for example; a greater exposure to sunlight may cause a person to have a darker skin colour. This is also known as acquired variation. Other examples of continuous variation in man are intelligence and weight.


Variation found in or among organizations could be physical (morphological) or behavioural (physiological).


Black or White?


While morphological and physiological variations contribute to adaptation in a range of species, they can also have important implications for conservation efforts. For example, understanding how genes influence body size and other characteristics could help researchers better understand the impacts of climate change on different populations. In addition, exploring variation in behavior may help us to better understand how human activities affect species interactions and other ecological processes.

One type of variation that is commonly found among species is morphological variation, or differences in physical characteristics such as size, shape, or color. This can be due to genetic factors, as well as environmental conditions such as temperature and humidity levels.





Variations in physical traits or outward appearances in organizations are known as morphological variations.


Examples include:


i.                   Height,


ii.                 weight,


iii.               colour of the eye, hair or coat of animals,


iv.               facial features


v.                 finger print patterns.



i.       Variation in Height: if you measure the heights of all the students in your class that are of the same age, there is likely to be a steady graduation from the students who are very short to those who are very tall.


ii.     Variations in weight can be due to genetic heredity or certain environmental factors such as i. lifestyle, diet or whether one is affected by an illness.


Weight of individual organisms in a population can vary greatly from newborn babies to teenagers and mature adults there is a continuous variation form one extreme to another (underweight to overweight).


iii.   Colour of the eye varies from person to person. It could be brown, amber, grey, green or blue. This continuous variation depends on the amount of melanin present in the iris of the eye. Brown eyes contain high levels of melanin while blue eyes contain low level of melanin.


iv.   Hair colour in humans varies from blonde, brown to black. There are many intermediate shades between light coloured hair and dark-coloured hair. Variations in fur colour can also be seen in animals such as cows and rabbits.


v.     Facial features: Although humans general look similar in physical form, our facial features vary. Some of our facial features like our nose or mouth resembles our parents but none looks exactly like theirs. The shapes of our face can range from oblong, round to squarish.


vi.   Fingerprints are patterns formed by the ridges in the dermis of the skin on our fingertips.


Variations in finger-prints can be broadly classified into; i.arch,


ii.        loop,


iii.      whorl and


iv.      compound.


Due to small variations in the fingerprints of different individuals, each person has a morphological variation.


Morphological variations in plants that are continuous are


i.       Height


ii.     shape of the body parts


iii.   leaf size


iv.   root size


v.     size of petals and sepals

vi. length of internodes.


















Types of Fingerprints


Human fingerprint patterns fall into three main groups: whorls, loops, and arches. Loops are the most common type, accounting for about 65 percent of all fingerprints. Whorls account for 30 percent of fingerprints, and arches for 5 percent. Despite these broad patterns, each individual has a unique set of fingerprints, which can be used as a means of personal identification.




1. Define evolution and variation.

2. State three differences between continuous and discontinuous variation.

3. What is morphological variation?

4. State four morphological variation in (i) plant (ii) animals (iii) humans.

5. Explain the role of genetic factors and environmental factors in morphological variation in organisms.

6. How does genetic and environmental factors influence the development of morphological variation in organisms?

7. How do continuous and discontinuous variations differ from each other? How do they impact the evolution and diversity of species?

8. What is meant by a population? How does natural selection act on populations to shape evolution and diversity?

9. How do evolutionary processes, such as gene mutation and genetic drift, impact the development of morphological variation in organisms?

10. How are morphological variations used in the identification of individual organisms? For example, how do forensic scientists use fingerprint patterns to identify criminals? How might genetic testing be used to identify individuals and populations?


Sub-Topic 2: Physiological Variation


Physiological variation refers to differences in the bodily functions of organisms.


Examples of physiological variation are;


i.       Disparities in ability to taste phenylthiocarbamide (PTC)


ii.     Ability to roll ones tongue and


iii.   Having different types of blood groups.


Members of the same species behave or react to certain things and conditions in their environment in different ways.


Examples of discontinuous variations in human population include:


i.       Some people can perceive smell while others cannot.


ii.     Some people (taster) may be able to detect taste of certain materials like bitter leaf, while others (non-taster) cannot. Similarly, some can detect high, moderate and low salt concentration in cooked meal while others cannot.


iii.   Few people can roll their tongues. There are no in-between or intermediates.


iv.   Some people can detect the taste of certain substances even at very low concentrations while others can only do so at very high concentrations e.g. phenylthiocarbamide (PTC).

v.     Every human possesses one of the four blood groups called A, B, AB and O. This is based on the cell factor called antigen.


The features of discontinuous variation are genetically determined. You cannot alter your blood group by changing your diet. They are under the control of a number of genes.


The absence of one gene for pigmentation causes albinism.

Examples of discontinuous variation in plants of the same species are;


i.       Colour of flower petals


ii.     Colour of fruits


iii.   Colour of seeds


iv.   Shape of seeds and fruits



1. Define physiological variation

2. Give three examples of Physiological variation in i. Animals





The knowledge of variations in human population is applied in many ways include the following: i. Crime Detection: Detectives use finger prints in identifying people suspected to have committed certain crimes. This is based on the assumption that no two persons possess exactly the same fingerprints and that human fingerprint remain the same throughout one’s life span. Hence, if the fingerprints of a suspect are exactly like those at the scene of a crime, the suspect might be held as being responsible for the crime.

Fingerprints on dangerous weapons can also be investigated to detect criminals such as assassins using riffles or pistol.























Fingerprint Analysis


Storing fingerprint records in computers has made it much easier for the FBI to identify latent fingerprints—fingerprints left at the scene of a crime.

Philippe Plailly/Science Photo Library/Photo Researchers, Inc.


ii.   Classification of the Human Race: variations in physical characteristics (e.g. skin colour) among human population have been used to classify the human race into four major grouping of Caucasoid, Negroid, Mongoloid and Australoid.


iii.  Blood Groups: Every human being belongs to any of the four blood groups A, B, AB or O. The knowledge of human blood group is used as follows:


a. Blood transfusion: If the transferred blood does not match that of the recipient, the

recipient’s blood will clump or agglutinate. Death, within minutes can result from the agglutination. The table below shows the blood groups that will clump and those that will not during blood transfusion.








A or O

B or AB


B or O

A or AB


A, B, AB, O




A, B, AB, O


People in blood group O can donate blood to people in all other groups. Hence, they are called universal donors. People in blood group AB can receive blood from people in other groups. Thus they are called universal recipients.


b.     Crime detection: When blood stains got from the scene of a crime is analysed, the result can be used by detectives to identify arrested suspects and hence detect the actual criminals.


c.      Determination of paternity: when there is a dispute as to the actual father of a baby, the knowledge of blood groups can be used to prove the paternity of the child. For example, if the baby’s blood falls under blood group AB and its mother is in blood group A, the baby’s genotype will be IA IB and the mother IA; or IA IA, certainly, the IB gene of the baby must have been inherited from the father. Supposing the alleged father is in blood group O, it is not likely that the baby belongs to him. If he is real father, the baby’s genotype ought to be be IA.




1. List four ways by which the knowledge variation in human population is useful to us.

2. State the blood group types that can be transmitted for individuals in blood groups A, AB, O




1. Which of these statements about variation is false?

(a) It is the difference found among members of the same species

(b)  Variations among members of the same species are usually more.

(c) Variations can be inherited.

(d) Variations can be continuous or discontinuous.

2. Which of the following is not a continuous variation?

(a) Height (b) weight (c) skin colour (d) ability to smell.

3. Which of the following is not one of the applications of the knowledge of variation?

(a) Determination of paternity (b) crime detection (c) Blood transfusion

(d) Determination of genotype

4. All the following are discontinuous variations except …………..

(a) Tongue rolling (b) crime detection (c) blood transfusion (d) determination of genotype

5. Which of the following is a discontinuous variation in plant?

(a) Height (b) root size (c) size of petals (d) shape of body parts.

6. Which of the following is a continuous variation?

(a) Height (b) weight (c) skin colour (d) ability to smell.

7. Determination of paternity is used for which of the following purposes?

(a) To detect criminals (b) To determine the actual father of a child

(c) To assess inheritance (d) To analyse the genetic makeup of individuals.

8. Which of the following is not a physical characteristic?

(a) Hair colour (b) blood group (c) ability to roll tongue (d) ability to taste.

9. The physical differences between human groups are due to……….variations.

(a) Genet (b) discrete (c) continuous (d) natural selection.

10. The human skin colour is a _______variation.

(a) Discrete (b) genet (c) continuous (d) natural selection.





(a). Define variation and evolution.


(b). Distinguish between morphological and physiological variations.


(a). What is the main difference between continuous and discontinuous variations?


(b) Explain two possible causes of variation.


(a) state five examples of continuous variations in (i) humans (ii) plants.


(b) State five examples of discontinuous variations in (i) human (ii) plants


4. In what ways is the knowledge of variation in human population useful to us?


5.   List and describe four types of human races.

6. How are variations useful in forensics and crime detection?

7. Outline three ways in which variations can be used to determine paternity.

8. Discuss how variations are used to analyze the genetic makeup of individuals.

9. How do variations allow us to understand evolution and adaptation?

10. Discuss how variations are useful for determining the potential benefits and risks of genetic modification.




Read about Evolution: Progressive changes in structure and anatomy of organisms and structural adaptations; Modern Biology for SSS by Ramalingam S.T. Pages 529-539