Evolution

• Evolution


  Descent with modification, the transformation of species through time, including the changes that occur within species and the origin of new species
• Hardy-Weinberg equilibrium


  A state where the frequencies of alleles and genotypes in a population will stay the same over generations
• A population in Hardy-Weinberg equilibrium is not evolving
• Assumptions for Hardy-Weinberg equilibrium


  • No mutation
  • Random mating
  • No gene flow
  • Very large population size
  • No natural selection
• Natural selection


  • The mechanism of evolution that explains how species can become better adapted to their environment
  • If a certain trait confers an advantage, then the individual possessing the trait may have more offspring than those with other traits
• If the trait is heritable

  The genes that give rise to the trait will be more common in the next generation
• Mutation


  A change in the DNA sequence of the gene
• A mutation may produce an allele that is selected against, selected for, or selectively neutral
• Harmful mutations are removed from the population by selection and will generally only be found in very low frequencies equal to the mutation rate
• Beneficial mutations will spread through the population through selection, although that initial spread is slow
• Genetic drift


  A mechanism of evolution in which allele frequencies of a population change over generations due to chance
• Genetic drift's effects tend to be stronger in small populations
• Genetic drift does not take into account an allele's benefit (or harm) to the individual that carries it
• Bottleneck effect


  An extreme example of genetic drift that happens when the size of a population is severely reduced
• Founder effect


  Occurs when a small group of individuals breaks off from a larger population to establish a colony
• Gene flow


  Refers to any movement of individuals, and/or the genetic material they carry, from one population to another
• If gene versions are carried to a population where those gene versions previously did not exist, gene flow can be a very important source of genetic variation
• Evidences of evolution


  • Biochemical
  • Embryological
  • Fossils
  • Anatomical
• Fossil record evidence

  • Fossils - remains or traces of an organism from the remote past
  • Physical evidence of former life from a period of time prior to recorded human history
  • Most fossils are found in layered sedimentary rocks - oldest fossils are on the lowest layers
• The fossil record attests to the fact that there has been a tremendous variety of living things
• Some extinct species had traits that were transitional between major groups of organisms, confirming that species are not fixed but can evolve into other species over time
• Fossils also provide evidence that the complex animals and plants of today evolved from simpler forms
• Evolution over many generations can result in the development of new varieties and species
• Failure to evolve in response to environmental changes can, and often does, lead to extinction
• Evidences of Evolution


  • BIOCHEMICAL
  • EMBRYOLOGICAL
  • ANATOMICAL
  • FOSSIL
• Fossils


  Remains or traces of an organism from the remote past
• Fossils are physical evidence of former life from a period of time prior to recorded human history
• Most fossils are found in layered sedimentary rocks, with the oldest fossils on the lowest layers
• Fossils give an undisputable record of past changes through vast periods of time
• Fossils attest to the fact that there has been a tremendous variety of living things
• Some extinct species had traits that were transitional between major groups of organisms
• The existence of transitional fossils confirms that species are not fixed but can evolve into other species over time
• Fossils provide evidence that the complex animals and plants of today were preceded by earlier simple ones
• Gaps or "missing links" in the fossil record are due to incomplete data collection
• As more is learned about the evolution of specific species lines, more gaps or "missing links" are filled with transitional fossil specimens
• One of the first gaps to be filled was between small bipedal dinosaurs and birds, with the discovery of the Archaeopteryx fossil
• Archaeopteryx had features of both dinosaurs and birds, verifying the assumption that birds had reptilian ancestors
• Homologous structures


  Structures that are similar but have different functions
• Similar body parts reflect shared ancestry, and structures may be used for different purposes in different groups but the same genes direct the development
• Vestigial structures


  Organs reduced in size and non-functioning remnants of similar organs in other species