EVOLUTION STUDIES Life Sciences

Hypothesis = a proposed explanation made on the basis of limited evidence as a starting point for further investigation. Theory = A system of ideas intended to explain something. Scientific Theory = Set of principles that explain and predict phenomena.

Evolution = the gradual development of something. Biological Evolution = involves changes that occur through descent involving genetic inheritance between generations.

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: 1)FOSSIL RECORD (Palaeontology):

2) MODIFICATION BY DESCENT (Homologous structures):

3) BIOGEOGRAPHY:

4) GENETICS:

Phylogeny Ontogeny 5) COMPARATIVE EMBRYOLOGY:

VARIATION SPECIES = a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. POPULATION = a community of animals, plants, or humans among whose members interbreeding occurs, all the inhabitants of a particular place.

Contributions to variation: 1)Meiosis: a) Crossing over =

1)Meiosis: b) Random arrangement of chromosomes =

2) Mutations =

3) Chance fertilisation =

4) Random mating =

Continuous variation = variation that has no limit on the value that can occur within a population. A line graph is used to represent it.

Discontinuous variation = variation in phenotypic traits in which types are grouped into discrete categories with few or no intermediate phenotypes.

Origin of the idea about origins (a historical development) Punctuated equilibrium = 1972 Niles Eldredge and Stephen Jay Gould

Theories of the process of Evolution 1) Lamarckism ( Jean Baptiste de Lamarck –1744–1829) The idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring (also known as heritability of acquired characteristics or soft inheritance).

Lamarck’s 1 st law: Law of Use & Disuse When certain organs became specially developed as a result of some environmental need, then the state of development is hereditary and can be passed on to the following generation.

Lamarck’s 2 nd law : Law of inheritance of acquired characteristics: The inheritance of the newly developed / lost characteristics by the following generation, thus the individual’s inherited the traits of their ancestors.

1) Characteristics acquired during the lifetime of a parent are not passed onto the offspring. 2) An athlete who develops a large muscle mass through training does not have children who already possess this large muscle mass. 3) Ernst Haeckel = In an attempt to disprove Lamarckism cut off the tails of mice for several generations. The babies born from this line of tailless mice still grew tails as long as their ancestors. Reasons to reject Lamarck’s theory:

Theories of the process of Evolution 2) Darwinism (Charles Darwin –1809–1882) The theory of the evolution of species by natural selection.

Observations upon which Darwin based his theory: 1)Organisms of a species produce a large number of offspring. 2)The offspring naturally show a great deal of variation. 3)Of the large number of offspring produced, only a few survive. 4)Characteristics are inherited from those surviving parents to the offspring.

Darwin's theory of evolution by natural selection: 1)Organisms produce a large number of offspring, that have a great deal of variation amongst them. 2)Some have favourable characteristics and some do not.

3) When there is a change in the environmental conditions or if there is competition, then organisms with characteristics which make them more suited, will survive, whilst organisms with characteristics that make them less suited, will die. 4) The organisms that survive, reproduce and thus pass on the favourable characteristic to their offspring. 5)The next generation will therefore have a higher proportion of individuals with the favourable characteristic.

Artificial Selection The intentional reproduction of individuals in a population that have desirable traits.

Artificial Selection - domesticated animals (selective breeding):

Artificial Selection – crop example:

Similarities between Natural Selection & Artificial Selection: 1)Want the strongest characteristics to be passed along generations. 2)Both rely on genotypic and phenotypic strength.

Differences between Natural Selection & Artificial Selection: Natural SelectionArtificial Selection 1) Driven by nature1) Driven by people 2) Variety centred within natural boundaries 2) Variety very different from nature 3) Occurs in natural populations 3) Occurs only in domesticated populations 4) Slow process – natural time 4) Fast process – driven by people.

Darwin travelled on the HMS Beagle and studied living organisms in their natural habitat.

Punctuated Equilibrium Darwinism indicates that evolution takes place through an accumulation of small or gradual changes that occur over a long period of time. This is supported by the many transitional fossils in the fossil record which show the progressive changes over time.

BUT Punctuated equilibrium explains the speed at which evolution takes place, as follows: 1) According to punctuated equilibrium, evolution is not gradual. 2) Evolution involves long periods of time where species do not change or change very little (known as equilibrium).

3) This alternates with (is punctuated by) short periods of time where rapid changes occur through natural selection. 4) As a result, new species are formed in a short period of time, relative to the long periods of no/little change. 5) This is supported by the absence of transitional fossils (usually termed missing links) indicating the period of rapid change.

Formation of new species Speciation = the formation of new and distinct species in the course of evolution. + impact on biodiversity. Extinction = the state or process of being or becoming extinct. – impact on biodiversity.

Speciation through geographic isolation: 1) If a population of a single species becomes separated by a geographical barrier (sea, river, mountain, lake), then the population splits into two populations. 2) There is now no gene flow between the two populations.

3) Since each population may be exposed to different environmental conditions, 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. 4) Even if the two populations were to mix again, they will not be able to reproduce with each other. They have thus become different species.

1) Gene Flow  During migration of individuals from one group to another, with interbreeding there is a mix of genes in the gene pool.

ALLOPATRIC SPECIATION – geographic isolation

Example: Darwin’s finches

Example: Galapagos tortoises

Example: Baobabs & Proteas

SYMPATRIC SPECIATION – due to natural preferences or influences

Keeping species separate (Mechanisms of reproductive isolation) When one species gives rise to two new species (speciation), the two species cannot reproduce with each other even if they mix. They remain as separate species due to mechanisms that restrict gene flow between them.

How each of the reproductive isolation mechanisms work: Breeding at different times of the year (prezygotic mechanism)

How each of the reproductive isolation mechanisms work: Species-specific courtship behaviour (animals)

How each of the reproductive isolation mechanisms work: Adaptation to different pollinators (plants)

How each of the reproductive isolation mechanisms work: Infertile offspring (e.g. mules)

Evolution in present times Natural selection and evolution are still occurring in present times. Any of the following examples can illustrate that: 1) The use of DDT and the consequent resistance to DDT in insects which can be explained in terms of natural selection

2) The 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

3) HIV resistance to anti-retroviral medication