Like all scientific theories, the theory of evolution has undergone some alteration since it was originally proposed - we know a lot more now than we did 150 years ago, and a lot of aspects of Darwin's original proposal have undergone a variety of different kinds of testing and subsequent modifications. One of the things that Darwin didn't apparently get quite right is the pacing of speciation. His primary concept of this phenomenon is generally referred to as "Darwinian Gradualism." Explain just what gradualism is. What is the alternative proposal offered by S.J. Gould and Niles Eldredge? What major body of evidence supports Gould and Eldredge's theory over Darwin's? And finally, are the two proposals mutually exclusive? (In other words, if one is a correct description of the pacing of evolutionary change, must the other necessarily be false?)