Darwin’s theory, modern synthetic theory, genetic drift

1. Introduction to Evolution

1. Evolution is the gradual change in the characteristics of organisms over generations.
2. It explains the diversity of life and how new species arise.
3. Key factors driving evolution include genetic variations, mutations, natural selection, genetic drift, and environmental influences.
4. Two major theories of evolution are Darwin’s Theory of Natural Selection and the Modern Synthetic Theory.

2. Darwin’s Theory of Evolution

1. Charles Darwin proposed the Theory of Natural Selection in his book On the Origin of Species (1859).
2. He observed variations among species during his voyage on the HMS Beagle, especially in the Galápagos Islands.
3. The main principles of Natural Selection are:
   • Variation: Differences exist within populations.
   • Overproduction: More offspring are produced than can survive.
   • Struggle for Existence: Organisms compete for limited resources.
   • Survival of the Fittest: Those with advantageous traits survive and reproduce.
   • Heredity: Beneficial traits are passed to the next generation.
4. Examples:
   • Industrial Melanism: Dark-colored moths became more common in polluted areas.
   • Darwin’s Finches: Different beak shapes evolved based on food sources.
   • Antibiotic Resistance: Bacteria evolve resistance to antibiotics over time.

3. Modern Synthetic Theory of Evolution

1. The Modern Synthetic Theory (also called the Neo-Darwinian Theory) combines Darwin’s Natural Selection with genetics.
2. Developed in the early 20th century by scientists like Ronald Fisher, J.B.S. Haldane, and Sewall Wright.
3. It explains evolution as a result of:
   • Mutations: Sudden changes in DNA creating variations.
   • Genetic Recombination: Mixing of genes during reproduction.
   • Gene Flow: Movement of genes between populations.
   • Genetic Drift: Random changes in gene frequency.
   • Natural Selection: Survival and reproduction of the fittest.
   • Isolation: Geographic or reproductive separation leading to new species.
4. It supports gradual evolution rather than sudden changes.

4. Genetic Drift

1. Genetic Drift is a random change in the frequency of alleles in a population.
2. It occurs due to chance events rather than natural selection.
3. Effects of genetic drift are significant in small populations.
4. Two main types:
   • Bottleneck Effect: A drastic reduction in population size due to natural disasters, leading to loss of genetic diversity.
   • Founder Effect: A small group separates from the main population, forming a new population with limited genetic variation.
5. Examples:
   • Pingelap Island: A small population in Micronesia has a high frequency of color blindness due to the founder effect.
   • American Bison: Their population was drastically reduced due to hunting, leading to genetic bottlenecks.

5. Differences Between Natural Selection and Genetic Drift

6. Importance of Evolution in Biology

1. Explains the origin of species and biodiversity.
2. Helps in understanding genetic diseases and antibiotic resistance.
3. Used in biotechnology, medicine, and conservation.
4. Supports theories in genetics, paleontology, and ecology.