 Both in the past and today, determining the boundaries of discrete races has proven to be most vexing and has led to great variations in the number of human races believed to be in existence. Thus, some thinkers categorized humans into only four distinct races (typically white or Caucasian, Black or African, yellow or Asian, and red or Native American), and downplayed any biological or phenotypical distinctions within racial groups (such as those between Scandinavians and Spaniards within the white or Caucasian race). Other thinkers classified humans into many more racial categories, for instance arguing that those humans “indigenous” to Europe could be distinguished into discrete Nordic, Alpine, and Mediterranean races.