Modern theories of evolution

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  • 1. MODERN THEORY OF EVOLUTION
  • 2. MODERN THEORY OF EVOLUTION (NEO- DARWINISM) Includes scientific evidence from genetics When the allele frequency of a population changes over successive generations When the changes are great enough, a new species may be formed A species is a group of individuals capable of interbreeding and producing fertile offspring
  • 3. CHANGES IN EVOLUTION DUE TO NATURAL SELECTION A great many offspring are produced but not all of them survive – population sizes stay fairly constant ‘Survival of the fittest’ – struggle for life for limited resources e.g. food, avoiding predators and disease, tolerance to changes in environmental conditions e.g. temp Individuals best adapted to their environment have a selective advantage – they are more likely to survive and produce offspring
  • 4. EVIDENCE FOR THE THEORY OF EVOLUTION – DARWIN SAID…… Each species living today arose from a pre- existing species All species have evolved from one ancestral type Natural selection provides a mechanism for one species to change into another
  • 5. FOSSILS K-Ar dating (potassium is found in many rocks and it decays to argon very slowly) Can date back 3000 million years Carbon dating is used on younger fossils (up to 50 000 years old) because it decays faster than potassium After dating, fossils are put into chronological order This gives an idea of how one group of organisms evolved into another
  • 6. PROBLEMS FROM FOSSIL EVIDENCE Fossilisation is rare because most organisms decay Better evidence comes form cell biology and biochemistry - by looking at the genetic code and physiological processes e.g. respiration These are similar in closely-related organisms
  • 7. NATURAL SELECTION ‘Fitness’ is the ability of an organism to pass on its alleles to subsequent generations, compared to other individuals of the same species The ‘fittest’ individual is one that produces large numbers of offspring that survive to reproduce themselves The genetic characteristics of a population gradually changes from generation to generation in response to changes in the environment
  • 8. NATURAL SELECTION AFFECTS THE GENE POOL Gene pool is all of the genes and their alleles present in a species There is an increase in the frequency of alleles that give an advantage, and a decrease in the frequency of alleles that do not give an advantage
  • 9. GENE MUTATIONS AND EVOLUTION Gene mutations are random events that result in a new allele Most are harmful Occasionally, one provides a new phenotype that has a selective advantage over other individuals in a population Over generations, the frequency of mutant alleles may increase (= micro-evolution) e.g. antibiotic resistance in bacteria; pesticide intolerance in insects
  • 10. GENE MUTATIONS AND EVOLUTION continued Changes at a higher level than species level is called macro-evolution This results in the formation of higher taxonomic groups e.g. new genera or classes.