 Evolution is the change in the inherited traits of a population of organisms through successive generations  Two factors at work:  Processes that constantly introduce variation in traits  Processes that make particular variants become more common or rare

 Variation is introduced to a population’s gene pool by:  Mutation: a heritable change in the nucleotide sequence of the genetic nucleic acid  Gene flow: introduction or loss of new alleles into the population through immigration or emigration  Genetic drift: stochastic shifts in allele frequencies in small populations  Natural selection: change in allele frequencies over generations due to differential survival and reproductive success of genotypes

 Point mutations are caused by random errors in the copying process (during transcription) Point mutation

 Chromosomal mutations occur when chromosomes fail to properly separate during meiosis Structural Modification Irregular Number

 Scientists disagree about how and why genes mutate  For a long time they believed that genetic mutations were unrelated to whatever consequences such mutations would have on the species.  Researchers have found evidence that cells might be able to "choose" which mutations will occur to give them an advantage in stressful situations.  For example, when starving, certain bacterial cells might generate multiple mutations. If the mutated cell survives, the mutation is passed on; cells that die take their unsuccessful mutations with them.  Flexibility in antibody production

Wilson & Bossert, 1971

 In each generation, some individuals may, just by chance, leave behind a few more descendents than other individuals  The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals  It happens to ALL populations—there’s no avoiding the vagaries of chance

 Fitness is a measure of the ability of an individual to produce viable offspring and contribute to future generations  Individuals vary in their relative fitness due partly to genetic differences among individuals and partly to environmental influences  Individuals with greatest fitness will contribute disproportionately to subsequent generations

 As the environment changes so do the fitness values of the genotypes  Some properties of fitness:  Fitness is a property of a genotype, not of an individual or a population  Individuals with the same genotype share the same fitness within the same environment  Fitness is measured over one generation or more

 Natural selection may not produce a “perfectly-engineered” trait  Reasons why natural selection might not produce perfection  Lack of necessary genetic variation  Constraints due to history  Trade-offs

 Adaptation is the evolutionary process whereby a population becomes better suited to its habitat  Important for an organism's survival  Adaptations may be:  Physiological  Morphological  Behavioral  Adaptation is the result of natural selection

 An adaptation is a feature that is common in a population because it provides some improved function  Adaptations are well fitted to their function  A vestigial structure is a feature that was an adaptation for the organism’s ancestor, but that evolved to be non-functional because the organism’s environment changed

 What are selection pressures in an organism’s environment?  Biotic factors  Predation  Competition  Mutualism  Abiotic factors  Resource availability  Physical conditions  Chemical conditions

Natural selection leads to adaptive radiation and speciation

“natural” or anthropogenic…

 No predators  Exponential growth  Environmental and crop damage

 Introduced in 1950  Initially highly effective  Reduced rabbits by 99%  Now mortality rate is less than 50%

 Over many generations, mutations produce successive, small, random changes in traits, which are then filtered by natural selection and the beneficial changes retained  Traits become suited to an organism's environment: these adjustments are called adaptations  Ok: Survival of the fittest Better: those that can --- survive

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