EVOLUTION

D.1.1     Outline the origin and development of pre-biotic Earth, including cooling and formation of and, sea and a reducing atmosphere.

D.1.2     Outline the experiments of Miller and Urey into the origin of organic compounds.

D.1.3     Discuss the hypothesis that the first catalysts responsible for polymeration reactions were clay mineral and RNA.

D.1.4     Discuss the possible role of RNA as the first molecule that could replicate.

D.1.5     Discuss a possible origin of membranes and prokaryotic cells.

D.1.6     Discuss the endosymbiotic theory for the origin of the four eukaryotic kingdoms.

D.1.6 D.1.1-D.1.6 The origin of life, suggested to have occurred about 3.8 x 10⁹ years ago and the conditions of the primitive atmosphere provides a good starting point for the option. The work of some scientists is particularly relevant:

                    Miller-Urey à formation of organic molecules

Matthews a  formation of polypeptides from hydrogen cyanide formed in the atmosphere from methane and ammonia

                    Katchalsky a catalytic action of clays – polypeptides à amino acids

Lynn Margulis à theory of heterotrophic ingestion of autotrophic prokaryotes )which developed symbiotically into double membraned chloroplasts and of bacteria which as symbionts developed into mitochondria.

D.2     The origin of species

D.2.1     State Lamarck’s theory of evolution by the inheritance of acquired characteristics.

D.2.2     Discuss the mechanism of, and lack of evidence for, the inheritance of acquired characteristics.

D.2.3     State the Darwin-Wallace theory of evolution as the natural selection and inheritance of favourable characteristics.

The Darwin-Wallace theory is accepted by most as the origin of ideas of evolution by means of natural selection. Extracts from Darwin’s writing may prove interesting stimulus material.

D.2.4     Describe experimental evidence for the process of natural selection, including bird predation on moths.

D.2.5     Discuss other theories for the origin of species including special creation and panspermia.

Panspermia is the theory that is concerned with the arrival of material from outer space. Special creation is mentioned by several religions, a study of all of them is not required.

D.2.6     Discuss the nature of the evidence for all these theories and the applicability of the scientific method for further investigation. 

Notes: All parts to be found in recent textbooks. The only evidence specified (and therefore required in examinations) is from paleontology, distribution, protein biochemistry and modern examples (D.3.11).

D.3.1     Describe the evidence for evolution as shown by the geographical distribution of living organisms, including the distribution of placental, marsupial and monotreme mammals.

D.3.2     Outline the main stages in the process of fossilisation.

D.3.3     Outline the method for the dating of rocks and fossils using radioisotopes, with reference to ¹⁴C and ⁴⁰K.

Details of the apparatus used is not required. Knowledge of the degree of accuracy and the choice of isotope to use is expected.

D.3.4     Define half life.

D.3.5     Deduce the approximate age of materials based on a simple decay curve for a radioisotope.

D.3.6     Outline the paleontological evidence for evolution using one example.

D.3.7     Explain the biochemical evidence provided by the universality of DNA and protein structures for the common ancestry of living organisms.

D.3.8     Explain how variations in specific molecules can indicate phylogeny.

D.3.9     Discuss how biochemical variations can be used as an evolutionary clock.

D.3.10     Explain the evidence for evolution provided by homologous anatomical structures including vertebrate embryos and the pentadactyl limb.

Drawings need show only the main features of relevance and need not be artistically accurate.

D.3.11    Describe modern examples of observed evolution including general biocide resistance, antibiotic resistance in bacteria, and heavy metal tolerance in plants.

Some well-documented evidence is to be found in recent accounts – such as the evolution of warfarin resistant strains of rat in response to the widespread use of the poison in the environment. Penicillin resistant strains have been selected to evolve as a result of widespread use of this antibiotic. Grasses resistant to toxic heavy metal colonise ‘spoil heaps’ as the individuals that can survive are selected and increase. A well-known example is DDT resistance in some mosquitoes.

Notes: The various pieces of this ‘puzzle’ are being discovered all the time, and more will undoubtedly be found over the period of this programme, although the major pieces are well known. Account will be taken (in examination paper mark schemes) of any unequivocal developments that do take place.

D.4.1     State the full classification of human beings from kingdom to sub-species.

D.4.2     Describe the major physical features, namely the adaptations for tree life, which define humans as primates.

D.4.3     Discuss anatomical and biochemical evidence which suggests that humans are a bipedal and neotenous of African ape, spread to colonise new areas.

D.4.4     Outline the trends illustrated by the fossils of Australopithecus including A. afarensis, A. africanus and A. robustus, and Homo including H. habilis, H. erectus and H. sapiens.

D.4.5     Discuss the possible ecology of these species and ecological changes which may have prompted their origin.

D.4.6      Discuss the incompleteness of the fossil record and the resulting uncertainties with respect to human evolution.

D.4.5- Knowledge of approximate dates and distribution for the named species is expected. Details of sub-species or particular groups (Cro-Magnon, Peking, etc.) is not required. Reasons for the incompleteness of the fossil record should be included.

 

D.4.7     Discuss the origin and consequences of bipedalism and increase in brain size.

D.4.8     State that the evolution of speech and the development of the reflective mind (consciousness) occurred at some time in the Homo lineage.

D.4.9     Describe the origin and main trends in tool making, religion, art, agriculture and technology.

D.4.10     Outline the difference between genetic and cultural evolution.

D.4.11     Discuss the relative importance of genetic and cultural evolution in the evolution of humans.

D.5 Neo-Darwinism    (AHL)

D.5.1     State that mutations are changes to genes or chromosomes due to chance, but with predictable frequencies.

D.5.2     Outline phenylketonuria (PKU) and industrial melanism as examples of gene mutation and Klinefelter’s syndrome as an example of chromosome mutation.

D.5.3     Explain that variation in a population results from the recombination of alleles during meiosis and fertilisation.

D.5.4.     Describe natural selection as leading to the increased reproduction of individuals with favourable variations.

D.5.5     State that adaptations (or micro-evolutionary steps) may occur as the result of an allele frequency increasing in a population’s gene pool over a number of generations.

D.5.6     Describe how the evolution of one species into another species involves the accumulation of many advantageous alleles in the gene pool of a population over a period of time.

D.5.7     Discuss ideas on the pace of evolution including gradualism and punctuated equilibrium.

Gradualism is the slow change from one to another, punctuated equilibrium, however implies long periods with no change and short periods of rapid evolution. The latter is gaining popularity as being more important than once thought. Mention could be made of the effects of volcanic eruptions and meteor impacts affecting evolution on Earth.

D.5.8     State that a species is part of a potentially interbreeding population having a common gene pool (cross reference 13.1.3).

D.5.9     Discuss the process of speciation in terms of migration, geographical or ecological isolation and adaptation leading to reproductive or genetic isolation of gene pools.

D.5.10   Describe an example to support macro-evolution (speciation) including ring species.

Two examples of ‘ring species’ are the herring gull and reindeer/caribou which are found in isolated groups or ‘races’ in a circum-polar distribution in the Northern Hemisphere. Groups next to each other are capable of interbreeding but at extremes of the range the difference is so great that they are regarded as different species.

If the frequency of alleles A and a in a parental generation are p and q, 

then p + q = 1 and in future generations AA:Aa:aa = p²:2pq:q²

D.6.1     Describe an adaptation in terms of the change in frequency of the alleles of a gene.

D.6.2     Explain how the Hardy-Weinberg equation: (p² + 2pq + q² = 1) is derived.

D.6.3     Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation.

D.6.4     State that the Hardy-Weinberg Principle can also be used to calculate allele, genotype and phenotype frequencies for genes with three or more alleles.

D.6.5     State the Hardy-Weinberg Principle and the conditions under which it applies.

For the principle to be followed it is must be assumed that a population is large with random mating and a constant allele frequency over time which implies no allele specific mortality, no mutation, no emigration and no immigration.

D.6.6     Describe one example of transient polymorphism, and sickle cell anaemia as an example of balanced polymorphism.

An example of transient polymorphism is industrial melanism. Sickle cell anaemia is an example of balanced polymorphism where heterozygotes (sickle-cell trait) have an advantage in malarial regions because they are fitter than either homozygote.

D.6.7     Describe how heterozygosity is advantageous for a gene pool.

This is clearly an advantage in sickle cell anaemia for a heterozygote individual. In general it maintains recessive alleles in a gene pool. Inbreeding leads to lack of heterozygosity and {inbreeding depression’. It is well known that plant breeders seek F₁ hybrid plants because of hybrid vigour.