- a) i) Explain the meaning of evolution
- a gradual change in living organisms from simple life forms to more complex forms over a long period of time.
ii) Differentiate organic evolution from chemical evolution as theories of origin of life
- organic evolution refers to the emergence of present forms of organisms gradually from pre-existing forms (some of which no longer exist)
- chemical evolution explains the origin of life as having occurred when simple chemical compounds reacted to form the simplest life forms
iii) What is special creation?
- maintains that the whole universe and all living organisms came into being due to the act of a supernatural being
b) Discuss the various kinds of evidence for evolution
- Fossils
- fossils are remains of organisms preserved in naturally occurring materials for many years
- they give evidence of types of plants/animals that existed at certain geological age/long ago/millions of years ago
- gives evidence of morphological/anatomical/structural changes that have taken place over a long period of time e.g. human skull, leg of horse
- Comparative anatomy
- gives evidence of relationship among organisms/gives evidence of a common ancestry of a group of organisms
- organisms have similar structures/organs performing the same function e.g. digestive system/ urinary system/nervous system/vestigial structures and vertebrate heart
- Divergence where the basic structural form is modified to serve different functions e.g. vertebrate forelimb/beak structure in birds/birds feet/parts of a flower. These are called homologous structures
- homologous structures have a common embryonic origin but are modified to perform different functions e.g. the pentadactyl limb
- adaptive radiation is a situation where organism have a homologous structure with common embryonic origin which is modified to perform different functions to adapt organisms to different ecological niches/habitats e.g. beaks of Darwinian finches(birds)
- Convergence is where different structures are modified to perform a similar function e.g. wings of birds and insects/eyes of humans and octopuses. These are called analogous structures
- Vestigial structures are greatly reduced in size and have ceased to function e.g. human appendix/caecium/coccix in humans, wings of kiwi (flightless bird), presence of hind limb pad in python, halters in insects, human hair nictitating membrane in human eye, human ear muscle, pelvic girdle in whale and third digit of wing of bird.
- Comparative embryology
- some embryos of different animals appear very similar thus showing relationship and possibility of a common ancestry
- e.g. different classes of vertebrates larvae of annelida and mollusca are similar (tocophere)
- Comparative serology/physiology
- these show biochemical and immunological comparisons of blood groups/components to show immunological similarities of tissues therefore showing relatedness of different organisms
- e.g. antigen antibody reactions, human blood groups/Rh factor reveal some phylogenic relationship among organisms/common ancestry
- Geographical distribution
- organisms differ in various geographical regions
- present continents are thought to have been a large land mass joined together/pangea/Eurasia/Gondwanaland
- present continents drifted apart from one land mass/continental drift
- as a result of continental drift isolation of organisms occurred bring about different patterns of evolution
- organisms in each continent evolved along different lines hence emergence of new species/divergence/convergence
Examples
- marsupials in Australia
- illama, jaguar, panther in S. America
- lion, camel in Africa
- tiger in Asia
- Cell biology (cytology)
- structures and functioning of cells are similar
- occurrence of organelles e.g. mitochondria in all cells/both plant and animal cells
- these point at a common ancestry
c) i) State the evolutionary characteristics that adopt human beings to the environment
– Brain
– Eyes
– Upright posture/bipedal locomotion
– prehensible arm/hand
– Speech
ii) State the ways in which Homo sapiens differs from Homo habilis
- standing upright/erect posture
- intellectual capacity/higher thinking capacity/bigger brain/higher brain capacity
- communication through language/speech
d) i) Explain Larmarck’s theory of evolution
- Inheritance of acquired characteristics/environment induces production of a favorable trait which is then inherited
ii) Explain why Lamarck’s theory of evolution is not accepted by biologists today
- evidence does not support Lamarck’s theory
- acquired characteristics are not inherited/inherited characteristics are found in reproductive cells only
iii) Explain Darwin’s theory of evolution
- inheritance of genetically acquired characteristics
- a character happens to appear spontaneously which gives advantage to an organism therefore adapted then inherited through natural selection
e) i) What is natural selection?
– Organisms with certain characteristics are favoured by the environment
Such organisms tend to survive and produce viable offspring
Others not favored are eliminated from subsequent generations
ii) With examples, explain how natural selection takes place
- organism with certain characteristics are favored by their environment
- such organisms tend to survive and produce viable offspring
- others not favored are eliminated from subsequent generations
- as the environmental conditions change the survival value of a character may alter with time so that characteristics which were favored may no longer have advantage and other characters may then become favorable
- if a favorable character is inherited, then offspring produce generations which are better adapted to survive in a population
- more offspring are produced than can survive which results in struggle for survival
- the fittest survive
iii) State the advantages of natural selection to organisms
- assist to eliminate disadvantageous characteristics/perpetuates advantageous characteristics
- allows better adapted organisms to survive adverse changes in the environment/less adapted organisms are eliminated
iv) State the ways in which sexual reproduction is important in the evolution of plants and animals
- brings about useful variations/desirable characters
- variations make offspring better adapted for survival/more resistant to diseases
- may lead to origin of new species
v) Explain the significance of mutation in evolution
– Mutation bring about variation which can be inherited
– Some of these variations are advantageous to the organism
– Others are disadvantageous
– The advantageous variations favour the organism to compete better in the struggle for survival
– This results into a more adapted organism to its environment or new species/varieties
– Those with disadvantageous characters will be discriminated against therefore eliminated from the population/death/perish
vi) Plain why it is only mutations in genes of gametes that influence evolution
- gametes form the new offspring
vii) How would you prove that evolution is still taking place?
- resistance of organism to antibiotics, pesticides and drugs
- new varieties of bacteria are resistant to certain antibiotics such as penicillin
- houseflies and mosquitoes are resistant to DDT
- Explain why some bacteria develop resistance to a drug after they have bee subjected to it for some time
- bacteria mutates/develops a new strain/chemical composition is altered hence is able to produce enzymes/chemicals which degrade the drug rendering it non-susceptible to the drug
- the new strain is favoured by selection pressure/ natural selection
f) How has industrial melaninism i.e. peppered moth contributed towards the mechanism of evolution
– This is an example of natural selection
– The peppered moth exists in two distinct forms, the speckled white form (normal form) and a melanic form (the black/dark)
– They usually rest on leaves and barks of trees that offer camouflage for protection
– Originally the “speckled white” form predominated the unpolluted area of England
– This colouration offered protection against predatory birds
– Due to industrial pollution tree barks have blackened with soot
– The white form underwent mutation
– A black variety/mutant emerged suddenly by mutation
– It had selective advantage over the white forms that were predated upon in the industrial areas
– The speckled white form is abundant in areas without soot/smoke
