Indeed, classifying the human species is difficult, as the book The Kinds of Mankind notes: “All we seem to be able to say is this: while not all human beings look like all the other human beings, and while we can clearly see a lot of the ways in which people look different, scientists still do not agree on exactly how many kinds of mankind there are.
उन्होंने यह भी निश्‍चित नहीं किया है कि लोगों को प्रजातियों में विभाजित करने के लिए हम किस आधार का प्रयोग कर सकते हैं ।