Evolution (change in gene proportions) by chance processes alone.
                                                            
                                                     
                        
                                                
                        
                        
                            The random process that leads to gradual changes in the frequency of alleles in a population from one generation to the next.
                                                            
                                                     
                        
                                                
                        
                        
                            Changes in allele frequency that result because the genes appearing in offspring are not a perfectly representative sampling of the parental genes.