Origin of Life: The universe is almost 20 billion years old. The Big Bang Theory explains the origin of the universe (singular huge explosion). Earth was formed about 4.5 billion years ago. There was no atmosphere on early Earth; water vapour, methane (CH₄), carbon dioxide (CO₂), and ammonia (NH₃) released from molten mass covered the surface. The UV rays from the sun broke up water into Hydrogen and Oxygen.

The theory of Chemical Evolution was proposed by Oparin and Haldane, stating that the first form of life could have come from pre-existing non-living organic molecules (e.g., RNA, protein). This was experimentally supported by S.L. Miller (1953), who created electric discharge in a closed flask containing CH₄, H₂, NH₂, and water vapour at 800°C, observing the formation of amino acids.

The first non-cellular forms of life could have originated 3 billion years ago (giant molecules like RNA, Protein, Polysaccharides). The first cellular forms of life appeared about 2000 million years ago and were likely single-cells in water (Biogenesis).

Evidence for Evolution:

• Paleontological Evidence: Study of fossils (remains of hard parts of life-forms found in rocks).

• Comparative Anatomy and Morphology:

  • Homologous Organs: Organs with the same fundamental structure/origin but different functions. Example: Forelimbs of Whales, Bats, Cheetah, and Human (all have humerus, radius, ulna, carpals, metacarpals, phalanges). This indicates Divergent Evolution (common ancestry).

  • Analogous Organs: Organs with different structure/origin but same function. Example: Wings of butterfly and birds; Eye of octopus and mammals; Flippers of Penguins and Dolphins. This indicates Convergent Evolution.

• Biochemical Evidence: Similarities in proteins and genes perform a given function among diverse organisms.

• Industrial Melanism: In England, before industrialization (1850s), white-winged moths were more abundant than dark-winged ones. After industrialization (1920s), tree trunks became dark due to smoke/soot, and the dark-winged moths survived better (predators couldn’t spot them). This is evolution by Natural Selection.

Adaptive Radiation: The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats).

• Darwin’s Finches: Small black birds on Galapagos Islands. From original seed-eating features, many other forms with altered beaks arose (insectivorous, vegetarian).

• Australian Marsupials: A number of marsupials, each different from the other (e.g., Tasmanian wolf, Tiger cat, Banded anteater), evolved from an ancestral stock, but all within the Australian island continent.

  When more than one adaptive radiation appears to have occurred in an isolated geographical area, it is called Convergent Evolution (e.g., Placental mammals in Australia resemble Marsupials; Placental Wolf vs. Tasmanian Wolf).

Biological Evolution: Lamarck (French naturalist) had said that evolution of life forms had occurred but driven by use and disuse of organs (e.g., Giraffes elongating their necks to eat tall leaves). This theory was discarded.

Charles Darwin sailed on H.M.S. Beagle and concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago. The fitness, according to Darwin, refers ultimately and only to reproductive fitness.

Two key concepts of Darwinian Theory of Evolution are Branching Descent and Natural Selection.

Mechanism of Evolution: Darwin did not explain how variations arise. Hugo de Vries, working on Evening Primrose, brought forth the idea of Mutations (large difference arising suddenly in a population). He believed mutation causes evolution and not the minor variations (heritable) that Darwin talked about. Mutations are random and directionless while Darwinian variations are small and directional. Evolution for Darwin was gradual, while de Vries believed mutation caused speciation and called it Saltation (single step large mutation).

Hardy-Weinberg Principle: In a given population, gene frequency (or allele frequency) remains stable and constant from generation to generation (Genetic Equilibrium). The sum of all allelic frequencies is 1. Represented as (p+q)² = p²  + 2pq + q²  = 1

Factors affecting Hardy-Weinberg equilibrium:

1. Gene Migration/Gene Flow (migration of section of population).

2. Genetic Drift (change in gene frequency by chance; Founder Effect).

3. Mutation.

4. Genetic Recombination.

5. Natural Selection.

   Natural Selection can lead to Stabilisation (more individuals acquire mean character value), Directional Change (more individuals acquire value other than mean), or Disruption (more individuals acquire peripheral character values).

A Brief Account of Evolution:

• First cellular forms: 2000 mya.

• Invertebrates: 500 mya.

• Jawless fish: 350 mya.

• Coelacanth: A fish caught in South Africa (1938) which was thought to be extinct. These were Lobefins that evolved into the first amphibians.

• Reptiles dominated the earth for 200 million years. Giant ferns (Pteridophytes) fell to form coal deposits.

• Dinosaurs suddenly disappeared 65 million years ago.

Origin and Evolution of Man:

• Dryopithecus and Ramapithecus (~15 mya): Hairy, walked like gorillas. Ramapithecus was more man-like; Dryopithecus more ape-like.

• Australopithecines (3-4 mya): Lived in East African grasslands. Hunted with stone weapons but essentially ate fruit.

• Homo habilis: First human-like being the hominid. Brain capacity 650-800cc. Probably did not eat meat.

• Homo erectus (1.5 mya): Large brain around 900cc. Probably ate meat.

• Neanderthal man: Brain size 1400cc. Lived in near east and central Asia (100,000-40,000 years back). Used hides to protect their body and buried their dead.

• Homo sapiens: Arose in Africa and moved across continents. Cave art developed ~18,000 years ago. Agriculture began ~10,000 years ago.