Most historians count 87 members of the party, although Stephen McCurdy in the includes Sarah Keyes—Margret Reed's mother—and Luis and Salvador, bringing the number to 90. Five people had already died before the party reached Truckee Lake: one from tuberculosis (Halloran), three from trauma (Snyder, Wolfinger, and Pike), and one from exposure (Hardkoop). A further 34 died between December 1846 and April 1847: twenty-five males and nine females. Several historians and other authorities have studied the mortalities to determine what factors may affect survival in nutritionally deprived individuals. Of the fifteen members of the snowshoe party, eight of the ten, men who set out died (Stanton, Dolan, Graves, Murphy, Antonio, Fosdick, Luis, and Salvador), but all five women survived. A professor at the University of Washington stated that the Donner Party episode is a "case study of demographically-mediated natural selection in action".