Evolution

 Evolution:

• Extinction:

  • The permanent disappearance of a species from Earth. This occurs when a species is unable to adapt to environmental changes or when its population declines to zero.

• Natural Selection:

  • The process by which organisms with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits on to the next generation.

• Phylogeny:

  • The evolutionary history and relationships among species or groups of organisms. Often represented by a phylogenetic tree, which shows how species are related through common ancestors.

• Speciation:

  • The formation of new and distinct species in the course of evolution. This occurs when populations of a species become reproductively isolated and accumulate genetic differences over time.

• Niche:

  • The role and position of a species within its environment, including how it gets its resources, its interactions with other species, and how it survives and reproduces.

• Mutation:

  • A change in the DNA sequence of an organism’s genome. Mutations can be beneficial, neutral, or harmful and are a key source of genetic variation.

• Mimicry:

  • An evolutionary adaptation in which one species evolves to resemble another species. This can provide protection (e.g., a harmless species mimicking a harmful one).

• Adaptation:

  • A genetic trait or behavior that improves an organism’s chances of survival and reproduction in its environment.

• Survival of the Fittest:

  • A phrase coined by Herbert Spencer, often associated with natural selection. It means that the organisms best adapted to their environment are more likely to survive and reproduce.

3. Theory of Evolution – Evidence to Support:

• Fossil Record:

  • Provides evidence of organisms that existed in the past and shows how species have changed over time through gradual transitions.

• Homologous Structures:

  • Body parts of different species that have a similar structure due to shared ancestry (e.g., the forelimbs of humans, whales, and bats).

• Vestigial Structures:

  • Features that have lost their original function through evolution (e.g., the human appendix or the pelvic bones in whales).

• Embryology:

  • The study of embryos shows that different species share similar developmental stages, indicating common ancestry.

• Molecular Evidence:

  • The comparison of DNA, proteins, and genetic sequences among species reveals evolutionary relationships and common ancestry.

• Biogeography:

  • The distribution of species across different geographic areas provides insights into how species evolved and adapted to different environments.

4. Patterns of Selection:

• Sexual Selection:

  • A form of natural selection where certain traits increase an organism's chances of attracting a mate, even if they don’t contribute to survival (e.g., peacock’s tail feathers).

• Stabilizing Selection:

  • Selection that favors the average individuals in a population, reducing variation. For example, human birth weight is subject to stabilizing selection, with extreme weights (too low or too high) leading to lower survival rates.

• Directional Selection:

  • Favors one extreme phenotype over others. Over time, this shifts the population toward that phenotype (e.g., longer beaks in birds if only long-beaked birds can access food).

• Disruptive Selection:

  • Favors both extremes of a phenotype range, leading to a bimodal distribution of traits. This can result in speciation (e.g., small and large beaks being favored over medium-sized beaks).

5. Selective Breeding vs. Natural Selection:

• Selective Breeding (Artificial Selection):

  • The intentional reproduction of organisms with desirable traits. Humans influence which individuals reproduce, commonly seen in pets, agriculture, and livestock.

• Natural Selection:

  • A natural process where organisms with traits that are best suited to their environment are more likely to survive and reproduce without human intervention.

Key Difference: Selective breeding is human-controlled, while natural selection is driven by environmental factors.

6. Speciation (Prezygotic, Postzygotic, Allopatric, Sympatric):

• Prezygotic Barriers: Prevent mating or fertilization from occurring.

  • Behavioral isolation (e.g., mating rituals).

  • Temporal isolation (different mating seasons).

  • Mechanical isolation (incompatible reproductive organs).

• Postzygotic Barriers: Occur after fertilization, preventing the proper development of a viable, fertile offspring.

  • Hybrid inviability (offspring don't survive to maturity).

  • Hybrid sterility (offspring, like mules, are sterile).

• Allopatric Speciation:

  • Occurs when populations are geographically isolated, leading to genetic divergence and eventual speciation.

• Sympatric Speciation:

  • Occurs when populations diverge into separate species within the same geographic area, often due to ecological or behavioral differences.

7. Evolutionary Mechanisms:

• Divergent Evolution:

  • When two related species evolve different traits due to different environmental pressures, often leading to speciation (e.g., Darwin’s finches with different beak shapes).

• Convergent Evolution:

  • Unrelated species evolve similar traits due to similar environmental pressures, despite not sharing a recent common ancestor (e.g., wings of birds and bats).

• Coevolution:

  • The process where two or more species influence each other’s evolution due to close ecological interactions (e.g., predator-prey dynamics, plant-pollinator relationships).

• Genetic Variation:

  • The differences in DNA among individuals in a population. It is the raw material for natural selection and evolution.

• Genetic Drift:

  • The random changes in allele frequencies in a population, especially in small populations, due to chance events.

8. Macroevolution:

• Abiogenesis:

  • The hypothesis that life arose from non-living matter through chemical processes, leading to the first simple life forms.

• Mass Extinctions:

  • Events where a significant proportion of species on Earth become extinct in a short period of time (e.g., the asteroid that killed the dinosaurs).

• Gradualism vs. Punctuated Equilibrium:

  • Gradualism: Evolution occurs slowly and steadily over long periods.

  • Punctuated Equilibrium: Evolution happens in bursts, with long periods of stability interrupted by rapid changes.

• Fossils:

  • The preserved remains or impressions of ancient organisms. Fossils provide direct evidence of how life forms have changed over time.

• Cladograms:

  • Diagrams that show evolutionary relationships among species. They are constructed using shared derived characteristics (synapomorphies) and show common ancestry.

9. Mutation – Neutral, Harmful, Beneficial, Homologous Genes, and Pseudogenes:

• Neutral Mutations:

  • Mutations that do not affect an organism’s fitness, often occurring in non-coding regions of DNA.

• Harmful Mutations:

  • Mutations that reduce an organism’s fitness, potentially leading to disease or malformations.

• Beneficial Mutations:

  • Mutations that improve an organism’s chances of survival or reproduction.

• Homologous Genes:

  • Genes shared by different species due to common ancestry. They may have similar functions but can evolve differently.

• Pseudogenes:

  • Genes that have lost their function due to mutations, often found in the genome as remnants of evolutionary history.

10. Human Impact – What Have We Done? What Can We Do?

• What Have We Done?

  • Habitat destruction: Deforestation, urbanization, pollution, and climate change have led to the loss of biodiversity.

  • Overexploitation: Overhunting, overfishing, and the illegal wildlife trade have caused species declines.

  • Introduction of invasive species: Non-native species introduced to new environments, often outcompeting or harming native species.

• What Can We Do?

  • Conservation efforts: Protect habitats, create wildlife corridors, and establish protected areas.

  • Sustainable practices: Promote sustainable agriculture, fishing, and resource use to prevent overexploitation.

  • Restoration ecology: Efforts to restore damaged ecosystems and protect endangered species.

  • Reduce carbon footprint: Addressing climate change by reducing greenhouse gas emissions and using renewable energy sources.