Biology · Lesson 22

Variation, evolution & adaptation

JAMBWAECNECO

What the syllabus asks

JAMB: Variation and its causes; evolution: theories and evidence; adaptation for survival

WAEC: Variation: morphological and physiological variation, continuous and discontinuous variation, causes and applications of variation; Evolution: theories of Lamarck and Darwin, evidence of evolution (fossils, comparative anatomy, embryology, biochemistry, geographical distribution); Adaptation: structural, behavioural and physiological adaptations to habitats, competition, camouflage, mimicry

NECO: Variation: morphological and physiological variation, continuous and discontinuous variation, causes and applications of variation; Evolution: theories of Lamarck and Darwin, evidence of evolution (fossils, comparative anatomy, embryology, biochemistry, geographical distribution); Adaptation: structural, behavioural and physiological adaptations to habitats, competition, camouflage, mimicry

What you will learn

Define variation and distinguish continuous from discontinuous variation.
Explain genetic and environmental causes of variation and its importance.
Plot and interpret graphs of variation.
State and evaluate the theories of Lamarck and Darwin.
Describe the evidence for evolution.
Describe structural, physiological and behavioural adaptations with Nigerian examples.
Explain artificial selection and simple examples of evolution in action.

Key points

Variation: differences within a species; morphological or physiological.
Continuous: range, many genes + environment, histogram/bell curve. Discontinuous: distinct groups, few genes, bar chart.
Genetic causes: meiosis, random fertilisation, mutation (new genes). Environmental causes: food, climate, disease; acquired traits not inherited.
Lamarck: use and disuse + inheritance of acquired characters (rejected; Weismann).
Darwin/Wallace: over-production, struggle, variation, survival of the fittest, inheritance.
Evidence: fossils (horse, Archaeopteryx), homologous and vestigial organs, embryos, DNA, distribution.
Adaptations: structural, physiological, behavioural; camouflage, mimicry.
Resistance in mosquitoes, bacteria and malaria parasites is evolution in action.

Start here: What is variation?

Look around your classroom. No two students are exactly alike: heights differ, so do skin tone, fingerprints, voices and blood groups. Even identical twins differ slightly in fingerprints. These differences among members of the same species are called variation.

Variation may be:

Morphological (structural, visible): height, weight, skin colour, shape of the nose, colour of the eyes, fingerprints, ear lobes (free or attached).
Physiological (functional, often invisible): blood group, ability to roll the tongue, ability to taste the chemical PTC, intelligence, rate of metabolism, resistance to disease.

Variation is not only in humans. A farmer's maize field has taller and shorter plants; goats in a herd differ in colour; some cowpea plants resist pests better than others.

Worked example 22.1

Classify these as morphological or physiological: (a) fingerprint pattern (b) blood group (c) height (d) tongue rolling.

Fingerprint and height are visible structures: morphological.
Blood group is in the chemistry of the blood: physiological.
Tongue rolling depends on muscle control: usually classed as physiological.

(a), (c) morphological; (b), (d) physiological

Try it yourself. Give two examples of variation in a population of goats.

Show solution

Coat colour, horn length, body size, milk yield (any two).

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Practice questions

1. The theory of natural selection was proposed by

Charles Darwin
Jean-Baptiste Lamarck
Gregor Mendel
Robert Hooke

Show answer

A: Charles Darwin
Darwin: "survival of the fittest". Lamarck proposed use and disuse.

2. Body mass in a class of students shows

discontinuous variation
no variation
only genetic variation
continuous variation

Show answer

D: continuous variation
It has a range of intermediate values.

3. An example of discontinuous variation is

weight
skin colour
blood group
height

Show answer

C: blood group
Clear categories.

4. A sudden change in genetic material is a

selection
mutation
variation
adaptation

Show answer

B: mutation
It may be inherited.

5. The theory of evolution by natural selection was proposed by

Charles Darwin
Jean Lamarck
Gregor Mendel
Louis Pasteur

Show answer

A: Charles Darwin
With Alfred Wallace.

Key words

Variation: Differences among individuals of the same species.
Continuous variation: Variation with a complete range of intermediate values.
Discontinuous variation: Variation in distinct, separate categories.
Morphological variation: Differences in visible form or structure.
Physiological variation: Differences in body function or chemistry, e.g. blood group, tasting PTC.
Mutation: A sudden change in a gene or chromosome.
Evolution: Gradual change in the inherited characteristics of populations over many generations.
Natural selection: Process by which better-adapted organisms survive and reproduce more.
Fossil: Preserved remains or traces of an organism from the distant past.
Homologous organs: Organs of similar basic structure and origin but different function.
Analogous organs: Organs with similar function but different structure and origin.
Vestigial organ: A reduced organ with little or no function, e.g. human appendix.

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