10.1 Evolution

1. Core Content

Definition of biological evolution

Difference between a hypothesis and a theory

The Theory of Evolution is regarded as a scientific theory since various hypotheses relating to evolution have been tested and verified over time

Evidence for Evolution

Role of the following as evidence for evolution:

• Fossil record – Link to Grade 10

• Biogeography – Link to Grade 10

• Modification by descent (homologous structures)

• Genetics

Variation

Definition of a biological species and a population

A review of the contribution of each of the following to variation that exists amongst individuals of the same species:

• Meiosis: Crossing over & Random arrangement of chromosomes

• Mutations

• Random fertilisation

• Random mating

Continuous and discontinuous variation

Ideas on evolution in the order of their origin are as follows:

• Lamarckism

• Darwinism

• Punctuated Equilibrium

Lamarckism (Jean Baptiste de Lamarck)

Lamarck used two 'laws' to explain evolution:

• 'Law' of use and disuse

• 'Law' of the inheritance of acquired characteristics

Reasons for Lamarck's theory being rejected

Darwinism (Charles Darwin)

Darwin's theory of evolution by natural selection:

• Organisms produce a large number of offspring.

• There is a great deal of variation amongst the offspring.

• Some have favourable characteristics and some do not.

• When there is a change in the environmental conditions or if there is competition,

• then organisms with characteristics, which make them more suited, survive

• whilst organisms with unfavourable characteristics, which make them less suited, die.

• The organisms that survive, reproduce

• and thus pass on the allele for the favourable characteristic to their offspring.

• The next generation will therefore have a higher proportion of individuals with the favourable characteristic.

• In this way, the characteristics of a population gradually change over a long period of time.

Punctuated Equilibrium (Eldredge and Gould)

Punctuated Equilibrium explains the speed at which evolution takes place:

• Evolution involves long periods of time where species do not change or change gradually through natural selection (known as equilibrium).

• This alternates with (is punctuated by) short periods of time where rapid changes occur through natural selection

• during which new species may form in a short period of time.

Artificial selection involving:

• A domesticated animal species

• A crop species

Formation of new species

Biological species concept: similar organisms that are capable of interbreeding to produce fertile offspring

Speciation and extinction and the effect of each on biodiversity

Speciation through geographic isolation:

• If a population of a single species

• becomes separated by a geographical barrier (sea, river, mountain, lake)

• then the population splits into two.

• There is now no gene flow between the two populations.

• Since each population may be exposed to different environmental conditions/the selection pressure may be different

• natural selection occurs independently in each of the two populations

• such that the individuals of the two populations become very different from each other

• genotypically and phenotypically.

• Even if the two populations were to mix again

• they will not be able to interbreed.

• The two populations are now different species.

Speciation through geographic isolation in ONE of the following:

• Galapagos finches

• Galapagos tortoises

• Plants on different land masses (linked to continental drift)

- Baobabs in Africa and Madagascar

- Proteas in South Africa and Australia

• Any example of mammals on different land masses

A brief outline of reproductive isolation mechanisms that help to keep species separate:

• Breeding at different times of the year

• Species-specific courtship behaviour

• Adaptation to different pollinators

• Infertile offspring

• Prevention of fertilisation

Any ONE example of natural selection and evolution in present times:

• Use of insecticides and consequent resistance to insecticides in insects

• Development of resistant strains of tuberculosis-causing bacteria (MDR and XDR) to antibiotics, due to mutations (variations) in bacteria and failure to complete antibiotic courses

• HIV resistance to antiretroviral medication

• Bill (beak) and body size of Galapagos finches