Darwinian Theory

• Charles Darwin declared that different species all evolve, and all organisms can trace their descent to a common ancestor.
• Darwin's theory is based on the idea of natural selection, which states that individuals with advantageous traits are more likely to survive and reproduce than those without them.
• Natural selection occurs when there is variation among members of a population, some individuals have heritable characteristics that make them better adapted to their environment, these individuals will be more successful at surviving and reproducing
• Evolution: The process by which new species arise from existing species through natural selection. Evolution ONLY EXCLUSIVELY happens in heritable traits. Darwin called this process "descent with modification".
• Darwin proposed a mechanism for evolution: natural selection. His concept was based on several key observations:

  • Traits are often heritable
  • More offspring are produced than the survival capacity.
• Fitness: An individual’s ability to survive long enough to produce offspring. It depends on many factors including genetics, environmental conditions, and interactions with other organisms.
• Organisms with a heritable trait that is advantageous to survive and reproduce are more likely to survive and reproduce, which can continue over generations, making the trait more common. This way, the population evolves in a way that they become more adapted to its environment.
• Natural selection & Phenotype distribution:

  1. Stabilizing selection

  Intermediate phenotypes are more fit than extreme ones. In a spectrum, it tends to narrow the curve.

  
• Natural selection & Phenotype distribution:

  2. Directional selection

  One extreme phenotype is more fit than all other phenotypes. This type of selection shifts the curve towards the favorable phenotype.

  
• Natural selection & Phenotype distribution:

  3. Disruptive selection

  Both extreme phenotypes are more fit than intermediate ones. This type of selection makes multiple peaks in the curve.

  
• Microevolution: The change in allele frequencies in a population over a relatively short period of time.