Evolution
Page 1: Fundamental Aspects of Evolution
Grade 12 overview: Introduction to the fundamental aspects of evolution (as per the transcript page title).
Page 2: Differences Between Microevolution and Macroevolution
Microevolution vs. Macroevolution (contrast in scope and timescale).
Examples listed in the transcript framing: Ornithischia, Sauropodomorpha, DINOSAURIA, Maniraptora, Saurischia, microevolution, MACROEVOLUTION. (Note: these appear as a contrastive heading or schematic rather than detailed definitions on this page.)
Page 3: Macro-evolution
Macro-evolution defined: the change that occurs at or above the level of species over long periods of time.
Patterns include trends and transformations such as the radiation of plants and the evolution of mammals.
Phylogeny = scientific study of relationships among species.
Phylogenetics = study of evolutionary relationships among groups of organisms which have been discovered through lines of evidence.
Page 4: Patterns in Macroevolution
(Content not explicitly provided in the transcript beyond the heading; note that patterns are acknowledged but not detailed on this page.)
Page 5: Adaptive Radiation and Extinction
Adaptive radiation: a burst of divergence from a single lineage to give rise to many new species from a single species.
New ecological niches become evident (example: Galapagos finches).
Mammals emerging after dinosaurs became extinct with many different species.
Extinction: can be frequent or rare within a lineage.
Mass extinction: occurs when many lineages are wiped out.
Page 6: Trends in Macroevolution
Increasing complexity in organisms: from Prokaryotes (no nucleus) and Eukaryotes (with nucleus), single-celled organisms, through Protists, to more complex organisms including humans with language.
Increasing body size and cranial capacity: notable during hominin evolution in about 2 imes10^6 years.
Evolving marine habitats to terrestrial; organisms developed the ability to fly.
Page 7: Time Morphological Change
Two models of morphological change over time:
(a) Gradualism model: slow, incremental changes over long periods.
(b) Punctuated equilibrium model: rapid changes during short periods, with long intervals of stasis.
Concept: The rate of change in evolution can be gradual or punctuated.
Page 8: a) Gradualism
Species evolve gradually by small changes over long periods of time.
Charles Darwin's Origin of Species as a foundational illustration of this theory.
Well-known example: Human evolution (Homo sapiens).
Page 9: b) Punctuated Equilibrium
Evolutionary change is not always gradual; it can occur in rapid bursts.
Key figure: Stephen Jay Gould (1941–2002), influential evolutionary biologist of the 20th century, who rethought Darwin’s theories and patterns of evolution.
Page 10: Gould’s Discoveries
Equilibrium: sometimes species didn’t change over millions of years or changed very slightly.
Short periods: rapid changes occurred due to natural selection.
New species emerged in a short period of time.
Absence of transitional fossils: attributed to rapid changes—fossils may not show gradual transitions.
Phenotypic modifications: species branch off from parents, then change slightly.
Volcanic eruptions and meteorites: caused great environmental changes.
Species adapt quickly: survival of the fittest.
Page 11: Natural Selection
Natural selection is based on Darwin’s theories.
Four evolutionary mechanisms observed:
More offspring are produced than required: producing more offspring than the environment can support.
Natural variation: variation within a population; no two individuals are the same because of different genes (example: beak size, muscular strength).
Change in the environment: leads to differential reproduction (survival of the fittest).
Traits were heritable: passed down from parents to offspring.
Darwin’s description: a process by which nature selects for survival those individuals best adapted to environmental conditions and reproduces offspring.
Page 12: Is Natural Selection Random?
Answer: No, it is not random.
Explanation: organisms that are better adapted survive; variations can arise (e.g., mutations and recombination of genes during sexual reproduction) in a random manner.
Does Natural Selection Result in Perfection?
Answer: No, natural selection does not produce perfection; it is a guiding process, not a driver toward perfect design.
Page 13: Natural Selection: What Causes Genetic Variation?
Germ-line point mutations: in eggs and sperm; main source of variation.
Duplication of genes or swapping their positions within chromosomes.
Whole chromosomes deleted or duplicated: polyploidy (heritable condition of possessing more than two complete sets of chromosomes).
Sexual reproduction: formation of new combinations of alleles through meiosis, chance fertilization, and random mating.
Therefore, a variety of genotypes are formed in offspring.
Page 14: Natural Selection: Why Offspring Differ from Parents?
Genetic variation: new combination of alleles.
Environmental factors: food, temperature, pH, sunlight all affect genotype.
Example: insufficient protein may affect development of big muscles.
Page 15: Natural Selection: Why Are Only Some Offspring Selected for Survival?
Selective forces: environmental pressures such as competition, predation, climatic factors, disease, and parasitism.
Some phenotypes are favored more than others, leading to differential reproduction.
Favorable phenotypic traits are selected: better suited to the environment, more likely to survive and reproduce.
Only a few unfavorable characteristics are expressed and less likely to reproduce.
Page 16: Result of Natural Selection
The new favorable genotype becomes more frequent in the population.
This increases the possibility of a new species emerging.
Page 17: Other Mechanisms of Evolution 1 — Polyploidy
Definition: the doubling or tripling of two sets of chromosomes.
Polyploidy is rare in animals but more important in the formation of new plant species.
Bread wheat has undergone hybridization and genetic modification and has strains that are:
diploid (2n)
tetraploid (4n)
hexaploidy (6n)
Represented as ext{diploid }(2n), ext{ tetraploid }(4n), ext{ hexaploidy }(6n) in discussions of chromosome sets.
Page 18: Other Mechanisms of Evolution 2 — Gene Flow
Definition: movement of genes between populations.
Occurs through:
Migration of organisms.
Movement of gametes (e.g., pollen blown to new locations).
Larvae dispersed by currents in the ocean.
Page 19: Other Mechanisms of Evolution — Genetic Drift
Definition: random changes in the frequency of characteristics in a population.
Result from chance in whether a trait is passed to the next generation.
Particularly important in small populations, where chance plays a larger role in determining which individuals reproduce and pass on their genes.
Page 20: Artificial Selection
Definition: the process of selecting and breeding organisms with desirable traits.
Widely used by farmers and breeders to cultivate new crops and new breeds of livestock.
Other human uses: agriculture, horticulture, transport, companionship, and leisure.
It mimics natural selection: only organisms with desirable traits reproduce.
Humans guide this process based on genetics and reproduction—an artificial version of natural selection.
Page 21: Importance of Artificial Selection
Plants: improved varieties of wheat, maize, and rice.
Animals: higher milk, wool, and meat production.
Organisms with better resistance to pests.
Improves quality and yield of crops.
Produces new strains of crops (e.g., Brussels sprouts and broccoli).
Produces new hybrid crops to meet human population demands (rice, maize, and wheat).
Adapts old crops to sustain inhospitable climates or environments (extreme temperatures, salinity, drought).
Develops social breeds (dogs for herding sheep).
Enhances nutritional value and flavour of fruits and vegetables.
Develops characteristics useful for storage, shipping, and processing of food.
Page 22: Artificial Selection in Crop Plants
Roughly 7,000 species of the 75,000 edible plants are used for food by humans.
Food crops come from domesticated varieties.
Domestication of wild plants led to new varieties of food due to altered genotypes and phenotypic changes.
All domesticated plants rely on humans to preserve them.
Cultigens = plants that show dependence on cultivation.
Page 23: Methods Used in Artificial Selection
Classic plant breeding: interbreeding (crossing) of closely or distantly related individuals to produce new crop varieties with desirable characteristics.
Example: mildew-resistant pea plant crossed with high-yielding pea plant to introduce mildew resistance without sacrificing high yields (crop production).
Modern plant breeding (includes):
Genetic engineering: selecting and transferring desirable traits from one plant to another by changing the genetic material.
Mutagenesis: production of mutants with desirable traits via chemicals or radiation.
Embryo rescue: rescuing seeds from valuable plants (e.g., orchids).
Polyploidy: generating new varieties via chromosome doubling or tripling (as noted earlier).
Page 24: Maize Domestication Characteristics
Characteristics selected during maize domestication include:
Reduced covering of the kernel (seed) of the teosinte plants.
Retention of kernels on the cob.
Erect habit with a single stalk — upright trait, preventing side branches.
Larger ear structure evident in modern maize plants.
Page 25: Differences Between Natural Selection and Artificial Selection
Natural Selection:
Occurs naturally via environmental selective factors.
Driven by nature.
Rate of change is slow.
Much variation.
Results in adaptation to the environment.
Artificial Selection:
Occurs artificially via human choice.
Driven by humans.
Rate of change is fast.
Less variation.
Results in improved livestock and crops.