Mechanisms of Population Change

 All around us because it’s the differences between living things  Some give organisms a survival advantage, while others cause disadvantage, others have no bearing on survival  Variation that is advantageous=Adaptation  Variability of individuals within same species arise from mutations and sexual reproduction and passed through generations

 Mutations are the random changes in DNA  Caused by chemicals, radiation or errors made while copying  Large populations over long time will have a more substantial number of mutations  Effects can be:  Neutral=no effect on reproductive success (fitness)  Harmful= selective disadvantage ▪ Sickle cell anemia-disorder that cause red blood cells to become crescent shaped instead of round and smooth causing blood clots and other medical problems  Beneficial = selective advantage ▪ Mutation that makes houseflies resistant to DDT in pesticides ▪ California ground squirrel have mutation that makes their blood better able to combat rattlesnake venom

 Production of offspring by union of sex cells from 2 DIFFERENT parents and 2 DIFFERENT sets of DNA means:  More traits become available because choices of mates  Different combos of genetic material  Random combos of genetic material 1000 males and 1000 females mean over 1 million different mating possibilities

 Only organisms best adapted to their environment will survive and pass on genetic characteristics

 Pg 165 Part 1 Human Variability (use data provided)  Evaluation  Synthesis  Pg 165 Part 2 Variations in Nature  Evaluation

 Compelling scientific theory that explains how organisms change and the diversity of species  To appreciate and judge the validity of this theory it is important to examine the evidence and review how we gain this knowledge  Major goal is to understand dramatic changes in populations over time

 What proof is there that present day species evolved from ancestral forms?  Many lines of investigation  Some direct observation and experiment, some more indirect  Gathered from  Fossil record  Geographic distribution of species  Comparative anatomy and embryology  Behavior  Plant and animal breeding  Biochemistry and genetics

 Species today are different from those living in the past  Progression of different species on Earth over time from simple forms in most distant past to increasingly complex forms  Radiometric dating helps scientists accurately determine ages of rocks and fossils  Living species & most closely matched fossils are typically located in the same geographic region

 Study of geographic distribution of life on earth  Proves species evolved isolated & independent after the breakup of the continents  Unique species (endemic)

 Homologous (similar structure different function) & vestigial (no useful function) features provide evidence of changes (pg 145)  Analogous features (similar in appearance and function but do not appear to have same evolutionary origin)  Embryonic development

 Compare biogeochemical characteristics  Proteins become increasingly different over time in different species  DNA sequences from different species that code for the same protein vary in number & order of 4 nucleotide bases Pg 147

 Process of humans selecting & breeding individuals with desired traits  Use it to produce dramatic changes in relatively short period of time  Provides evidence that this can happen over longer period of time & less dramatically  Pg 148 cabbage

 Worksheets “Variation among species” and “Evidence for Evolution”

 How do theories explain evolution on a global scale?  Theory  model that accounts for all known scientific evidence as completely as possible  Provides plausible explanation of how things in nature are related  Helps scientists to make testable predictions

 Early 1800s  New very simple species arose spontaneously from non living matter (spontaneous generation) and gradually became more complex  Organisms had “force” or “desire” that lead them to change  Thought organisms acquired traits/ characteristics that were passed down the generation  Giraffe got long neck over years of stretching and wanting to reach the food

 ZTeU ZTeU  wAk wAk

 Observations #1 Individuals within any species exhibit many inherited variations #2 Every generation produces far more offspring than can survive to reproduce #3 Populations of species tend to remain stable in size

 Inferences #1 Individuals of same species are in constant struggle for survival #2 Individuals with more favorable variations are more likely to survive & pass these variations on, survival is not random (survival of the fittest) #3 Since individuals with more favorable variations contribute proportionately more offspring to succeeding generations their favorable inherited variations will become more common (natural selection)

 Faster cheetah caught more prey, therefore stayed healthier, could better compete for mates and provided better for their young. Therefore that cheetah “survived” better and passed on the favorable trait of being fast to the future generations.

 Peppered Moth case study

Gradualism  Theory that speciation happens slowly Punctuated Equilibrium  Theory that species evolve rapidly followed by a period of little of no change  Pg 160 The earth has experienced periods of rapid diversification (divergent evoltion) as well as mass extinction

 Speciation is a theory that explains how new species form (wood bison and plains bison pg 157)  3 step process (allopatric speciation) for animals in isolation  Physical barrier separates interbreeding therefore they mutate separately  Natural selection works on separate populations and they evolve separately  In time differences become pronounced and they can no longer be sexually compatible

 Worksheet “Are you fit enough?”