Throughout the history of the Christian church there have been moments of significant theological crisis, and we are currently in the midst of another. But our pressing question is not "Who is Jesus?" (as it was in the fourth century) nor "How can we be saved?" (as it was in the sixteenth). Now it is, "What is a human being?" In many communities that claim the name "Christian," even people who can provide correct answers to the first two questions are currently confused when it comes to the third. This book is intended to help all such readers understand how they should, as faithful Christians, respond to this crucially important question, and how they should live as a result. At the same time, it seeks to equip these serious Christians to recognize the non-Christian roots of the powerful, competing ideas of "the human" that they encounter every day, both in contemporary society and in contemporary churches, and to have the courage to reject them. For these unbiblical ideas, when embedded in a church, do damage to Christian faith and life. They are destructive cuckoos in the Christian nest.