VCE BIOLOGY UNIT 4 EXAM REVISION Gary Simpson

Contents Development of Evolutionary Theory Evolutionary Relationships Natural Selection Evidence of Evolution Patterns of Evolution Change in Populations Population Equilibrium Hominid Evolution Biological, Cultural and Technological Evolution Human Intervention

Evolution Jean-Baptiste Lemarck – suggested a theory of acquired characteristics suggesting that obvious changes could be made within one generation. Alfred Wallace – proposed a theory of evolution similar to Darwin’s Charles Darwin – credited with the theory of evolution based on natural selection to explain the diversity of species extant and extinct on planet earth.

Natural Selection The theory of evolution is based on the concept of natural selection. This assumes that in any population: There is variation with respect to various traits Some traits are better suited to survival than others Not all individuals will survive and reproduce Those individuals that do survive and reproduce will have suitable traits These suitable traits will slowly increase over time.

Geological Time Earth believed to be 4500 million years old. Evolution based upon natural selection needs a great deal of time.

Evidence for Evolution Fossil record Fossils can take the form of trace, cast, amber or preserved body parts. The process of fossilisation is a delicate one and is easily disturbed and the fossils destroyed. Fossils can be dated using various techniques; eg C14 of K/Ar

Evidence for Evolution Process of Fossilisation An organism dies and is buried quickly in an area they can remain undisturbed. Oxygen is excluded. Hard parts of the organism leach out which leaves a cast which is filled by minerals The mould is buried in sediment which is covered by repeated layers and left for a considerable time. Fossils are remarkably rare!

Evidence for Evolution Biogeography Many extant species can be shown to have arisen from a common extinct species. For example flightless birds are found on the continents that once formed the land mass known as Gondwana and offer evidence for the existence of that land mass.

Evidence for Evolution Comparative Anatomy Homologous structures are structures with the same origin and similar structure but which may have different functions. Analogous structures are structures which have similar function but lack a common origin or similar structure.

Evidence for Evolution Comparative Embryology The embryo’s of mammals can be compared to species of other phyla and to fossil records to indicate ancestral connections.

Evidence for Evolution Comparative Biochemistry – DNA Molecular hybridisation – samples of single stranded DNA from two species are placed together and encouraged to bond together. The new strand is then heated. The higher the temperature reached before the strand breaks, the greater the number of bonds and therefore the closer related are the two species. DNA sequencing – when the DNA sequences of species are compared, the fewer the differences the closer the species are related.

Evidence for Evolution Comparative Biochemistry – Proteins Many organisms produce the same proteins and enzymes. As proteins are the expression of genes, this suggests that many species have the same or very similar genetic information, which in turn suggests a common ancestral species.

Patterns of Evolution Divergent Evolution – homologous structures are commonly used as evidence for divergent evolution where species evolve from a common ancestor adapting to different environments. Convergent Evolution – analogous structures are commonly used for evidence of convergent evolution where species from different ancestors respond to similar environmental pressures in different ways developing different structures to achieve the same function.

Changes in Populations Gene Pools – a term used to describe all the genetic information within a population. Individuals within a gene pool inherit different combinations of alleles due to: Independent assortment of chromosomes during metaphase 1 Crossing over of chromatids in prophase 1 Random nature of fertilisation Random nature of mating

Changes in Populations Allele Frequency – the term used to describe the abundance of any given allele in a population, relative to other alleles at the same locus. Allele frequencies remain unchanged if: There is no mutation The population is infinitely large The population is isolated Mating is random All individuals survive and reproduce successfully.

Factors affecting population equilibrium Founder Effect – describes when a few individuals leave an existing population and establish a new population somewhere else. The new population may have a gene pool with limited diversity and different allele frequencies to the original population.

Factors affecting population equilibrium Genetic Drift – chance events increase or decrease variations in alleles over time. These chance events may cause an allele to disappear from the gene pool or to become the only allele present for a particular trait. This is more likely in small populations than large populations.

Factors affecting population equilibrium Bottle Neck – this is an extreme example of genetic drift. A very small group of individuals of a species may survive some catastrophic event and are then the basis of future generations, but with very limited genetic diversity and a reduced ability to adapt to future environmental change.

Factors affecting population equilibrium Variation Within species Environmental effects Genetic Effects Sexual Reproduction

Adaptations Speciation – when a new species arises from existing species. Extinction – when a species disappears from the planet.

Allopatric Speciation Individuals within a population are separated by a barrier that prevents migration. Difference selection pressures are applied to the two populations. The allele frequencies of the two populations diverge. Over time two species arise that can no longer successfully interbreed.

Isolating Mechanisms Pre-reproductive Post-reproductive Things that stop populations physically mating; eg. Geographic features, timing of breeding, behavioural mechanisms, morphological mechanisms. Post-reproductive Phenomenon that stop offspring developing into adults; eg. High gamete mortality, high zygote mortality, hybrid sterility.

Evolutionary Relationships Phylogenetic trees – start with a common ancestral species and then show the points at which new species have branched off. Cladograms – a diagram showing the relationship between organisms based on their evolutionary history.

Determining Species Relatedness DNA sequencing – the more similar the sequence of bases of two species the more likely they are to share a common ancestor. DNA-DNA hybridisation – DNA is extracted from 2 species and caused to combine. Mitochondrial DNA – mtDNA mutates at a steady state and can be used as a molecular clock. Chloroplast DNA – has changed very little over time. Proteins – comparing the amino acid sequences of proteins.

Hominid Evolution Primates – a group of mammals that have binocular vision, flat nails, exposed, sensitive finger pads, and large brain relative to body size. Hominins – a sub-group of primates that walk upright and have relatively large brains. Hominids – a sub-group of hominins containing all the human and human like species. Genus Homo – our genus of which we are the only extant species.

Common Features of Hominids Relatively large brain for body size 5 digits on hand and feet Opposable thumbs Large forward facing faces 4 upper and 4 lower incisors Flexible skeletons Generally small litters with extended periods of intensive parenting.

Human Evolution Out of Africa Theory Regional Continuity Theory Homo erectus arose in Africa and migrated throughout the world. At a later point in time Homo sapiens arose in Africa and then migrated throughout the world replacing H. erectus. Regional Continuity Theory Homo erectus arose in Africa and migrated throughout the world. At a later point in time Homo sapiens independently arose throughout the world replacing H. erectus.

Biological, Cultural and Technological Evolution

Human Intervention Selective Breeding Domestication Artificial Cloning Genetic Engineering