4.2 Fundamental aspects of evolution.pptx

F U N D A M E N TA L ASPECTS OF E VO LU T I O N Grade 12 S Y N O P S I S O F E VO LU T I O N T H E M E S 1. Origin about the theory of evolution 2. Fundamental aspects of evolution 3. Formation of new species 4. Hominid studies 5. Evolution in present times RECAP Evolution is the gradual ch...

F U N D A M E N TA L ASPECTS OF E VO LU T I O N Grade 12 S Y N O P S I S O F E VO LU T I O N T H E M E S 1. Origin about the theory of evolution 2. Fundamental aspects of evolution 3. Formation of new species 4. Hominid studies 5. Evolution in present times RECAP Evolution is the gradual change or development of something over time. Biological evolution is the change in the gene pool of a population during a course of time. Can arise due to processes such as mutation, natural selection and genetic drift. It is descent with modification Can cover: Macro-evolution: Development of new species from pre-existing species over many generations Micro-evolution: Evolution within a single species M AC R O - E VO LU T I O N Change that occurs above species level Includes remarkable evolutionary trends and transformations, such as the origin of mammals and radiation of flowering plants Involves studying patterns on the tree of life, and deciphering the processes that would have brought these patterns about TREE OF LIFE  TREE OF LIFE Tree of life: Metaphor describing the relationship of all life on earth, within an evolutionary context. Phylogenetics: Study of evolutionary relationships among groups of organisms which had been discovered through lines of evidence. Cladogram vs Phylogenetic tree Cladogram: shows relatedness between groups of individuals, based on shared characteristics Phylogenetic tree: shows the degree of similarity. Branch length usually dictates genetic similarity Cladogram Phylogenetic tree P AT T E R N S S E E N I N T H E TREE OF LIFE 1. Stasis/Equilibrium Case of “living fossils”: little to no change/modifications for long periods of time P AT T E R N S S E E N I N T H E TREE OF LIFE 2. Lineage-splitting (speciation) Speciation: Formation of new and distinct species in the course of evolution Patterns and times of speciation can be identified by constructing and examining phylogenies Especially in reference to lines of descent and relationships among groups of organisms Phylogeny may show cladogenesis or anagenesis P AT T E R N S S E E N I N T H E TREE OF LIFE 2. Lineage-splitting (speciation) Cladogenesis: Evolutionary splitting event where a parent species splits into two distinct species – forming a clade Clade: Group of life forms consisting of a common ancestor and all off its descendants P AT T E R N S S E E N I N T H E TREE OF LIFE 2. Lineage-splitting (speciation) Anagenesis: Ancestral species gradually accumulates changes and eventually is sufficiently distinct enough from the original form to be labelled as a new form. Anagenesis trends are often associated with micro-evolutionary trends, whereas cladogenesis are seen as macro-evolutionary CLADOGENESIS VS. ANAGENESIS P AT T E R N S S E E N I N T H E T R E E O F L I F E 3. Adaptive radiation Refers to a burst of divergence from single lineage – giving rise to many new species from a single ancestor. Form of macro-evolution Occurs due to a need to fill up new ecological niches (e.g.: finches of Galapagos islands). Anagenesi Cladogenes Adaptive s is radiation P AT T E R N S S E E N I N T H E T R E E O F L I F E 3. Adaptive radiation Examples: ~315 m.y.a., reptiles became land-living as they no longer required to be on land for reproduction due to advancement of the amniotic egg. Later, a rapid burst of diversification gave rise to birds After the extinction of the dinosaurs, there was an explosion of mammalian evolution – due to the climatic change and extinction of dinosaurs, many niches were left empty to fill. P AT T E R N S S E E N I N T H E T R E E O F L I F E 4. Extinction May be a frequent or rare event within a lineage or can occur simultaneously across many lineages (mass extinction). Every lineage has some chance of extinction occurring. TRENDS SEEN IN MACRO- Increasing complexity From single cellular prokaryotes to highly complex eukaryotes E VO LU T I O N Primitive to complex societies Increasing body size Coupled with increased cranial capacity Change in habitats Evolving from marine habitats to terrestrial habitats before flying. R AT E O F C H A N G E I N E VO LU T I O N Paleontologists suggest two possible paces of evolution: Gradualism Punctuated equilibrium Scientists are attempting to determine which pace is more typical of evolution R AT E O F C H A N G E I N E VO LU T I O N - G RA D U A L I S M Species evolve gradually by small changes over long periods of time As suggested in Darwin’s Origin of Species E.g.: evolution of humans Follows “linear” pattern of evolution, rather than spontaneous bursts of rapid evolution Slow, gradual changes in the evolution of Homo sapiens is well documented RAT E O F C H A N G E I N E V O LU T I O N – P U N C T U AT E D E Q U I L I B R I U M Idea established by Stephen Jay Gould (1941 – 2002) Refers to the speed at which evolution takes place Long periods of time where species did not change or underwent very little change Alternated by rapid changes, brought on by natural selection Resulting in new species being formed in relatively short periods of time Supported by the absence of transitional fossils (“missing links”) Predicted that events such as volcanic eruptions and meteor impacts created major environmental changes that would speed up the rate of evolution. N AT U R A L S E L E C T I O N Darwin’s idea of natural selection is the proposed basic mechanism of evolution. Darwin made four observations that led him to develop the idea of natural selection: 1. More offspring are produced than are required Populations produce higher numbers than what the environment can support, yet population sizes remain stable over time 2. Natural variation Variation between individuals within a single species 3. A change in the environment leads to differential reproduction Better adapted individuals would be more likely to survive and go on to reproduce more = differential reproduction (“survival of the fittest”). 4. Characteristics (traits) were heritable Traits were passed from parents to offspring N AT U R A L S E L E C T I O N Natural selection only operates on variation of in inherited characteristics Process whereby nature selects for the individuals that are best adapted to environmental conditions, and as a result, would produce the most offspring Natural selection provides a mechanism for evolution  Organisms produce larger number of offspring than necessary 1 E V O LU T I O N BY N AT U R A L Variation occurs in the offspring 2 D A RW I N ’ S T H E O RY O F Some offspring will have favourable characteristics 3 When the environment changes or competition arises, organisms with 4 favourable characteristics will be better adapted Organisms less suited to the changed environment will die out and decrease in 5 number in the population SELECTION Favourable organisms will survive, reproduce and increase in number in the 6 overall population Next generations will have a higher proportion of favourable organisms 7 Changes in the individuals of a species over time will lead to speciation 8 NB! Page N AT U R A L S E L E C T I O N Is natural selection a random process? Natural selection is not a random process The organisms selected for survival are those better adapted to the environment The ways that variations arise are random (e.g., mutations and gene recombination) Does natural selection result in perfection? No population or single organism is perfectly adapted to its environment Natural selection should be considered as a process – it is mechanical and has no goals  TO DO NOW  Revise pages 218 – 224  Learning Activity 2 – excluding Q7 N AT U R A L S E L E C T I O N A C T S O N G E N E T I C V A R I AT I O N Must be some genetic variation within the population – so environmental conditions can select the best adapted individuals What causes genetic variation? 1. Germ-line mutations – main source of genetic variation 2. Duplication of genes or swapping positions within chromosomes 3. Duplication or deletion of whole chromosomes 4. Sexual reproduction – results in formations of new combinations of alleles Results in a variety of genotypes formed in the offspring N AT U R A L S E L E C T I O N A C T S O N G E N E T I C V A R I AT I O N Must be some genetic variation within the population – so environmental conditions can select the best adapted individuals What causes genetic variation? 1. Germ-line mutations – main source of genetic variation 2. Duplication of genes or swapping positions within chromosomes 3. Duplication or deletion of whole chromosomes 4. Sexual reproduction – results in formations of new combinations of alleles Results in a variety of genotypes formed in the offspring  N AT U R A L S E L E C T I O N A C T S O N G E N E T I C V A R I AT I O N Why do offspring phenotypes differ from their parents? Genetic variation (new combinations of alleles) Effect of environmental factors on the expression of the genotype In this manner, a variety of phenotypes can be formed.  N AT U R A L S E L E C T I O N A C T S O N G E N E T I C V A R I AT I O N Why are only some offspring selected for survival? Selective forces (environmental pressures) such as competition, predation, climatic factors, disease and parasitism will favour some phenotypes more than others – resulting in differential reproduction Individuals with favourable phenotypic characteristics are selected Being better suited to the environment will allow a higher successful reproductive rate Individuals with unfavourable phenotypic variations will be less likely to reproduce successfully  N AT U R A L S E L E C T I O N A C T S O N G E N E T I C V A R I AT I O N Why are only some offspring selected for survival? Selective forces (environmental pressures) Learning such as competition, predation, climatic factors, disease and parasitism will favour some phenotypes Activity 3 more than others – resulting in differential reproduction Individuals with favourable phenotypic Page 226 characteristics are selected Being better suited to the environment will allow a higher successful reproductive rate Individuals with unfavourable phenotypic variations will be less likely to reproduce successfully  N AT U R A L S E L E C T I O N E X A M P L E – PEPPERED MOTH Biston betularia Pre-industrial revolution in England Original moth colour was light – blended in with grown on trees Genetic colour variant of dark-coloured moths – but these were easy targets for predators After start of industrial revolution Advancement of coal-based industry resulted in lichen being killed off of trees, making trees darker Darker coloured moth variant less likely to be targeted by predators Era of cleaner air Modern air pollution controls has resulted in lichens growing back – natural selection now favours lighter moths varieties Darker variants becoming rare again O T H E R M E C H A N I S M S O F E VO LU T I O N 1. Polyploidy The doubling or trebling of the two basic sets of chromosomes Often involves hybridisation between two species – resulting in offspring with unique genetic compositions who are unable to mate with previous generations I.e. instantly become new species Rare occurrence in animals, but is immensely important in the evolution of new species of plants Bread wheat (6n) arose by two separate events of hybridisation causing polyploidy. O T H E R M E C H A N I S M S O F E VO LU T I O N 2. Gene flow The movement of genes between populations Happens through the migration of organisms or the movement of gametes Larvae dispersal by sea  O T H E R M E C H A N I S M S O F E VO LU T I O N 3. Genetic drift Process that produces random changes in frequency of characteristics (alleles) in a population Results from a role that chance plays in whether a given trait will be passed on to the next generation Chance plays a greater role in smaller populations  TO DO NOW  Revise pages 225 - 228  Learning Activity 4 (Pg 228 – 229) A RT I F I C I A L S E L E C T I O N Farmers and breeders have used the wild variations to cultivate their crops and create new breeds Artificial selection: Process of selecting and breeding organisms with desirable characteristics to produce offspring with those characteristics that would be of some use to humans Only those organisms with the desired traits are allowed to reproduce Artificial selection (guided by humans) is an artificial form of natural selection and evolution (guided by nature) N AT U R A L V S A R T I F I C I A L S E L E C T I O N Artificial selection Natural selection Process occurs... Artificially via human Naturally via choice environmental selective agents Driven by Man Nature Rate of change Fast Slow Amount of variation Less variation More variation Consequence Improved crops and Adaptation to livestock environment I M P O RTA N C E O F A RT I F I C I A L S E L E C T I O N Domestication of wild plants and animals for desirable traits Produce disease and pest resistance Improve crop quality and yield Produce new strains of crops Produce new hybrid crops (high-yielding varieties) Adapt old crops to enable them to grow in inhospitable climates and areas Develop specialized breeds for specific purposes Enhance nutritional value and flavours Develop characteristics useful for storage, shipping and food processing A RT I F I C I A L S E L E C T I O N What is inbreeding and outbreeding? Inbreeding is the mating of closely related individuals Extreme example: self-fertilization (wheat species) To select and continue particular characteristics Often leads to loss of vigour and poor survival as the offspring can become homozygous for higher proportion of undesirable recessive genes Outbreeding is the mating of individuals not closely related Resultant offspring tougher and more fertile with a greater chance of survival Offspring probably heterozygous with undesirable recessive alleles being masked by normal dominant alleles A RT I F I C I A L S E L E C T I O N – C A N I S FA M I L I A R I S Gene pool of dogs – 78 chromosomes – has a large amount of hidden genetic variability, which can be expressed under selective forces Grey wolf (Canis lupus) – ancestral dog species – gave rise to five ancient breeds which in turn gave rise to modern, distinct breeds When wolves were domesticated, humans subconsciously bred wolves that retained immature characteristics – such as tameness, playfulness and subservience A RT I F I C I A L S E L E C T I O N – C R O P P L A N T S 90% of the world’s food comes from only 15 species of plants What artificial selection methods are used in plant breeding? Classical plant breeding: Deliberate interbreeding of closely or distantly related individuals to bring about varieties with combined, desirable characteristics Modern plant breeding, which includes: Genetic engineering, which uses molecular techniques to select, transfer or change genetic material Mutagenesis, production of mutants that may give rise to desirable characteristics Embryo rescue, from seeds of valuable plants Polyploidy, can be induced by chemicals and has been important in generating new varieties and even species A RT I F I C I A L S E L E C T I O N – Z E A M A Y S ~10 000 years ago, early native Americans changed a wild grass into maize by selective breeding Characteristics that were selected: Reduced covering of kernel (seed) – reducing hard outer covering (glume) Retention of kernels on the cob – previously, kernels would shatter off cob Erect habit with a single stalk – previously, many side branches with dispersed energy and kernels Larger ear structure – previously, tiny ears of “corn” with 6 – 12 kernels  TO DO NOW  Revise pages 229 - 233  Learning Activity 6 and 7  Complete summative Learning Activity 8