Key Points

The Big Bang theory explains the origin of the universe, which is approximately 13.8 billion years old. Earth was formed about 4.5 billion years ago with a reducing atmosphere containing gases like methane ($\text{CH}_4$), ammonia ($\text{NH}_3$), water vapor, and carbon dioxide.

In 1953, S.L. Miller demonstrated chemical evolution by creating early Earth's conditions in a lab. He passed an electric discharge through a flask with $\text{CH}_4, \text{H}_2, \text{NH}_3$, and water vapor at $800^{\circ}\text{C}$, resulting in the formation of amino acids.

The theory of spontaneous generation (life from decaying matter) was disproven by Louis Pasteur. 'Panspermia' suggested life came from outer space. Oparin and Haldane proposed that life originated from pre-existing non-living organic molecules (chemical evolution).

Charles Darwin proposed that evolution occurs through natural selection. Individuals with heritable traits that provide a survival or reproductive advantage (higher fitness) are more likely to pass those traits to the next generation.

Homologous structures have a common evolutionary origin but different functions (e.g., forelimbs of whales, bats, and humans), showing divergent evolution. Analogous structures have different origins but similar functions (e.g., wings of birds and butterflies), showing convergent evolution.

Fossils, the preserved remains of ancient organisms in sedimentary rocks, provide direct evidence for evolution. The fossil record shows that life forms have changed over time and that many species have gone extinct.

In England, the population of moths shifted from predominantly light-colored to dark-colored (melanised) after the Industrial Revolution. This occurred because soot darkened the trees, making dark moths better camouflaged from predators, demonstrating natural selection in action.

Adaptive radiation is the evolutionary process where species from a common ancestor diversify rapidly into new forms, particularly when a change in the environment makes new resources available. Key examples are Darwin's finches and Australian marsupials.

Lamarck proposed the 'inheritance of acquired characteristics' through use and disuse of organs, a theory that has been discredited. Darwin's theory is based on natural selection acting upon heritable variations within a population.

Hugo de Vries proposed that evolution is caused by sudden, large-scale mutations, which he called saltation (single-step large mutation). He believed this, not Darwin's small, gradual variations, was the source of new species.

This principle states that allele frequencies in a population are stable and constant from generation to generation (genetic equilibrium). It is expressed by the equation $p^2 + 2pq + q^2 = 1$, where p and q are the frequencies of two alleles.

Evolution occurs when the Hardy-Weinberg equilibrium is disturbed. The five factors that cause this are gene migration (gene flow), genetic drift, mutation, genetic recombination, and natural selection.

Genetic drift refers to random changes in allele frequencies due to chance events, which has a greater impact on small populations. The founder effect is a type of genetic drift where a new population is established by a small number of individuals from a larger population.

Natural selection can be stabilizing (favors average individuals), directional (favors one extreme phenotype), or disruptive (favors individuals at both extremes of the phenotypic range).

First cellular life appeared about 2000 million years ago (mya). Invertebrates formed by 500 mya. Jawless fish evolved around 350 mya. Dinosaurs disappeared about 65 mya, which led to the rise of mammals.

Human evolution includes Australopithecines (walked upright), Homo habilis (brain capacity 650-800cc, used tools), Homo erectus (brain capacity 900cc, likely ate meat), Neanderthal man (brain capacity 1400cc), and Homo sapiens (modern humans).