natural select and arti

• Types of Natural Selection

  • Directional Selection
  • Stabilizing Selection
  • Disruptive or Diversifying Selection
• Directional Selection


  • When the environment changes, populations will often undergo directional selection, which selects for phenotypes at one end of the spectrum of existing variation
  • Organisms with a phenotype that is well matched to their existing environment are more likely to succeed in this phase
• Directional Selection


  • Giraffe's long neck is selected naturally and is an example of directional selection
  • Due to this adaptation, giraffes can reach to the topmost leaves to avoid food competition
• Stabilizing Selection


  • Happens when intermediate phenotypes are more likely to survive in the environment
  • Occurs when the population stabilizes on a particular trait value and genetic diversity decreases
• Stabilizing Selection


  • In a population of plants, those that are short may not get enough sunlight, but those that are tall may be subjected to wind damage. This results in an increase in the number of medium-height plants and a decrease in very tall and very short plants
• Disruptive or Diversifying Selection

  • Happens when extreme phenotypes are more likely to respond to the environment
  • Occurs when both extreme traits are favored in an environment
• Disruptive or Diversifying Selection

  • An example of disruptive selection is how squirrel tail-length favors either short tails in order to hide from predators on the ground or long tails for balancing up in trees
• Artificial Selection


  Selective breeding that is imposed by an external entity, usually humans, in order to enhance the frequency of desirable features
• Artificial Selection


  • Farmers have cultivated numerous crops from the wild mustard by considering the desired traits in breeding them; thus, different kinds of vegetables were produced
• Nonrandom Mating


  The selected probability of mating with another individual in the population
• Forms of Nonrandom Mating

  • Inbreeding
  • Outbreeding or Assertive Breeding
• Inbreeding


  • When individuals are more likely to mate with their close relatives than with distant relatives
  • The concern with this form of breeding is that the chances of inheriting disease disorders caused by harmful recessive genes are greater
  • Inbreeding may also decrease the capacity of the population to survive and reproduce, a condition called Inbreeding depression
• Inbreeding


  • When a royal family preferred marrying only other royal members to keep their bloodlines "pure"
• Outbreeding or Assertive Breeding

  • Happens when individuals select distant relatives than close relatives as their partners
  • Individuals are more likely to pair with identical phenotypes
• Evolution

  The process by which nature selects, from the genetic diversity of a population, those traits that would make an individual more likely to survive and reproduce in a continuously changing environment
• Theories of evolution did not start with the Theory of Evolution by Charles Darwin. It started in the 18th century that many naturalists began to state the idea that life might not have been fixed since creation.
• Jean-Baptiste Lamarck

  A botanical and zoological systematist, as a founder of invertebrate paleontology, and as an evolutionary theorist. In his own day, his theory of evolution was generally rejected as plausible, unsubstantiated, or heretical.
• Lamarck's Theory of Evolution

  1. Theory of Use/Need

  2. Theory of Disuse

  3. Theory of Inheritance of Acquired Characteristics
• Theory of Use/Need

  Giraffes used to have short necks. However, their increase in population caused a shortage in their food supply on the ground; thus, they tried to eat the leaves on the trees to survive. To reach these leaves, giraffes needed to stretch their necks, as Lamarck proposed. Such continuous stretching over time enabled the next generation of giraffes to have longer necks
• Theory of Disuse

  If an animal continues not to use its body part, the size of the body part or organ will gradually decline for multiple generations before it ultimately disappears. Since ancient snakes didn't use their feet, according to the principle of disuse, these body parts gradually were underdeveloped. Vestigial body parts or organs are those that have become functionless during evolution.
• Theory of Inheritance of Acquired Characteristics

  Organisms have inherited their traits from their parents, and that they will therefore transfer them on to the descendants of the next generation.
• In several cases, Lamarck's hypotheses of usage and disuse and acquired inheritance are proved to be false. Although evolution occurs in generations of reproduction, Lamarck was incorrect in thinking that traits developed over a lifetime will be passed along to offspring Because the correct mechanism of inheritance is that genes are passed along from generation to generation.
• Charles Darwin

  English naturalist whose scientific theory of evolution by natural selection became the foundation of modern evolutionary studies.
• Darwin's Expedition

  Charles Darwin sailed around the world from 1831–1836 as a naturalist aboard the HMS Beagle. His experiences and observations helped him develop the theory of evolution through natural selection. He went to Galapagos Island and observe the Finches birds
• Types of Evolution

  • Divergent Evolution
  • Convergent Evolution
• Divergent Evolution

  Two groups of the same species evolve different traits within those groups in order to accommodate for differing environmental and social pressures. Traits that arise through convergent evolution are referred to as 'homologous structures'.
• Homologous Structure

  Organisms that came from the same ancestor with the same body structure exposed to different environment, tend to develop different body function.
• Convergent Evolution

  Species occupy similar ecological niches and adapt in similar ways in response to similar selective pressures. Traits that arise through convergent evolution are referred to as 'analogous structures'.
• Analogous Structure

  Organisms that are not from the same ancestor and with different body structure exposed to same environment tend to develop the same body function.