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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
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
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
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
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
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
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
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
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.