Climate changes thats what im guessing .. not too sure though ... sorry 
        
             
        
        
        
They occur in germ cell DNA, which are the cells that create sperm or Ova. For every 85 million nucleotides assembled in DNA during human sperm or Ova production, One will be a mutation
        
             
        
        
        
Initially, when scientists were first using the taxonomy system to classify living organisms there were only considered to be 2 kingdoms: plants and animals. However, when the microscope was invented, scientists were able to observe differences in organisms at the cellular level! They were also able to observe microscopic living organisms like bacteria that they had not been able to observe before. Scientists realized it was necessary to add 4 new kingdoms to account for the observations they had not seen before the invention of the microscope.
 
        
             
        
        
        
Answer:
The average trait value changed in one direction.(In this case, larger size)
Explanation:
In evolution a natural selection can be disruptive, directional or stabilizing
In stabilizing no extreme trait is favored hence provides intermediate values .
Disruptive selection both extreme traits are favored over the intermediate trait.
Directional, the enviroment will favor the survival of one trait hence a change in direction either towards the left or the right.
In the case of swallow cliff mortality, selection favored the larger size.
 
        
             
        
        
        
Answer:
The correct answer is option d. "Many species that moved into North America from South America outcompeted the endemic taxa and still exist today".
Explanation:
The Great American Biotic Interchange (GABI) was an historical period at which numerous species from South America migrated to North America, and numerous species from North America migrated to South America because of the formation of the Isthmus of Panama. During this event, many species that moved into North America from South America outcompeted the endemic taxa and still exist today. The species that successfully immigrated to South America and exist today were mostly small mammals, such as armadillos and opossums.