Blog #4:Describe the three types of selection: directional, stabilizing and disruptive and give an example of each in your own words.

                                                                                               

                            

                            Directional selection is a function of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction.  In directional selection, the different allele increases  in frequency independently of its dominance relative to other alleles.  Directional selection stands in opposite to balancing selection where selection may favor multiple alleles, and is the same as purifying selection which removes harmful mutations from a population.  An example can be found in the breeding of the greyhound dog.  Early breeders were interested in dog with the greatest speed.  They carefully selected from a group of hounds those who ran the fastest.  From their offspring, the greyhound breeders again selected those dogs who ran the fastest.  By continuing this selection for those dogs who ran faster than most of the hound dog population, they gradually produced a dog who could run up to 64km/h (40mph).

                       

                        
                          Stabilizing selection  is also a type of natural selection where genetic diversity decreases as the population stabilizes on a particular trait value.  This is probably the most common mechanism of action for natural selection.  Stabilizing selection commonly uses negative selection to select against extreme values of the character.  Stabilizing selection acts to prevent divergence of form and function.  An example of stabilizing selection is human birth weight.  Babies of low weight lose heat more quickly and get ill from infectious diseases easily,  but babies with large body weight are difficult to deliver through the pelvis.  

                      
                        
                        Disruptive selection favors the extremes of a range of selection.  Disruptive selection refers to natural selection that favors phenotypic extremes. An example of this is a population of seed-eating birds with beaks that range in size, so that big beaks are best adapted to eating big seeds, small beaks are best adapted to small seeds, and medium beaks are best adapted to medium seeds. Now suppose that the source of medium seeds goes extinct it looses its food source, selection favors the big and small beaks. 

                    

Blog #3: Explain what microevolution is? What are the three ways that variation occurs?

                                                             

      

                        Microevolution is a change in gene frequency within a population.  This change is because of four different processes: mutation, artificial and natural selection, gene flow and genetic drift.  Evolution at this scale can be observed over short periods of time — for example, between one generation and the next, the frequency of a gene for pesticide resistance in a population of crop pests increases. Such a change might come about because natural selection favored the gene, because the population received new immigrants carrying the gene, because some nonresistant genes mutated to the resistant version, or because of random genetic drift from one generation to the next.  Microevolution is reductionist meaning an approach to understanding the nature of complex things by reducing them to the interactions of their parts.  


                    Variation can occur three different ways.  Variation can occur when all the organisms produce more offspring then one can survive to adulthood and reproduce, many of these offspring will die without reproduction.  Another way that variation can occur is when the variation is heritable, if it's in the parents it's passed on to the offspring.  A third way that variation can occur is by an absence of mutation.
 

Blog #2: Why is fossil record hard to interpret?

                         

                                
                            The fossil record is hard to interpret because paleontologists sometimes they find the remains of an entire organism or sometimes the find parts of a it.  It's hard to explain a fossil because it could come in different shapes and sizes.  Sometimes it can be the sand or the layers of dirt that covers the fossil that makes it so hard to interpret.  Paleontologist have to be careful not to break the fossil when interpreting it.  It is very hard to interpret a fossil when it's a small animal because the bones of the fossils are so small.  But when interpreting a large animal, it takes long to explain it but its still very hard.  They often have to build an extinct species from a few fossil bits- bones, shells, leaves or pollen.  When paleontologists study a fossil they look for related similarities and differences between the fossil and living organisms.  Paleontologists also have to determine the age of the fossil, which is really important. 

Blog #1: Why is evolution a theory not a law?

              A theory is more of an explanation.  A law is a pattern that natural phenomena follow.  So they're two different things.  A law is great for predicting events, because we expect the events to follow the pattern.  But the law won't explain why events follow the pattern. For that we need a theory.  Both theories and laws can turn out to be wrong, and must be tested by considering what evidence we should find if the theory or law were false, and then looking for such evidence.  A law must be confirmed and broadly agreed upon through the process of inductive reasoning.  A theory is a well-supported body of interconnected statements that explains observations and can be used to make testable predictions.  Evolution is not a law because evolution describes the mechanisms of how and why organisms change over time.  In all honesty, no scientists disbelieve evolution at this point.  There is disagreement on some of the details of the theory – the details of the how and why – but not the big questions that things evolve or even the general ideas of how and why.