Examples of Natural Selection Short Note | Evolution Class 12 Notes

In this article we will discuss about Examples of natural selection:- 1. Industrial melanism, 2. DDT-resistant mosquitoes and 3. Sickle cell anemia

1. INDUSTRIAL MELANISM

• This phenomenon was studied by Bernard Kettlewell in England
• Peppered moth exist in two forms black and grey

Early 1800s

• • Preindustrial England
  • Low pollution
  • Plenty of Lichen grow on tree
  • Grey color moth population is increased
  • Black color moth is very few

Late 1800s

• • Industries developed and that area was polluted
  • All lichens are disappear
  • Grey color moth population reduced
  • Black color moth is increased

Mid 1900s

• • In factories use electric current and pollution controls
  • Again lichens are grown on tree
  • Grey color moth population is increased
  • Black color moth is very few

2. DDT-RESISTANT MOSQUITOES

• Mosquitoes are vectors of diseases like malaria and elephantiasis
• Earlier the mosquito more DDT sensitive
• DDT as an insecticide introduced in 1940s
• Certain individuals are resistant to DDT
• This resistant mosquito reproduce more and more offspring’s
• The resistant population are evolved as a selective advantage against insecticides

3. SICKLE CELL ANEMIA

• Genetically transmitted disease of the blood
• Caused by presence of abnormal hemoglobin S
  • Hb Hb – Normal
  • Hb Hs – Sickle cell trait
  • Hs Hs – Sickle cell anemia
• Individuals with heterozygous condition have better chances of survival, hence are selected by nature